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  • 1.
    André, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Graham, Daniel B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Karlsson, T.
    KTH Royal Inst Technol, Sch Elect Engn, Dept Space & Plasma Phys, Stockholm, Sweden.
    Wieser, G. Stenberg
    Swedish Inst Space Phys, Kiruna, Sweden.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Norgren, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    Lab Phys & Chim Environm & Espace, Orleans, France.
    Rubin, M.
    Univ Bern, Phys Inst, Bern, Switzerland.
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany.
    Lower hybrid waves at comet 67P/Churyumov-Gerasimenko2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S29-S38Article in journal (Refereed)
    Abstract [en]

    We investigate the generation of waves in the lower hybrid frequency range by density gradients in the near plasma environment of comet 67P/Churyumov-Gerasimenko. When the plasma is dominated by water ions from the comet, a situation with magnetized electrons and unmagnetized ions is favourable for the generation of lower hybrid waves. These waves can transfer energy between ions and electrons and reshape the plasma environment of the comet. We consider cometocentric distances out to a few hundred km. We find that when the electron motion is not significantly interrupted by collisions with neutrals, large average gradients within tens of km of the comet, as well as often observed local large density gradients at larger distances, are often likely to be favourable for the generation of lower hybrid waves. Overall, we find that waves in the lower hybrid frequency range are likely to be common in the near plasma environment.

  • 2.
    Bergman, Sofia
    et al.
    Swedish Inst Space Phys, Kiruna, Sweden; Umeå Univ, Dept Phys, Umeå, Sweden.
    Stenberg Wieser, Gabriella
    Swedish Inst Space Phys, Kiruna, Sweden.
    Wieser, Martin
    Swedish Inst Space Phys, Kiruna, Sweden.
    Johansson, Fredrik Leffe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    The Influence of Varying Spacecraft Potentials and Debye Lengths on In Situ Low-Energy Ion Measurements2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 4, article id e2020JA027870Article in journal (Refereed)
    Abstract [en]

    Low-energy ions are difficult to measure, mainly due to spacecraft charging. The ions are attracted to or repelled from the charged surface prior to detection, which changes both the energy and travel direction of the ions. This results in distortions of the data, and the changed travel directions distort the effective field of view (FOV) of the instrument performing the measurements. The ion composition analyzer (RPC-ICA) was measuring positive ions down to an energy of a few eV around comet 67P/Churyumov-Gerasimenko. Low-energy ions play important parts in processes in the cometary environment, but the FOV of RPC-ICA has been shown to get severely distorted at low ion energies. Several factors are believed to affect the distortion level. In this study we use the Spacecraft Plasma Interaction Software (SPIS) to investigate the influence of varying spacecraft potentials and Debye lengths on the FOV distortion of RPC-ICA. We show that the distortion level is dependent on the Debye length of the surrounding plasma, but the sensitivity varies substantially between different viewing directions of the instrument. We also show that a small nonlinearity exists in the relation between FOV distortion, ion energy, and spacecraft potential, mainly caused by the photoemission and bulk flow of the cometary plasma.

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    FULLTEXT01
  • 3.
    Bergman, Sofia
    et al.
    Swedish Inst Space Phys, Kiruna, Sweden.;Umea Univ, Dept Phys, Umea, Sweden..
    Wieser, Gabriella Stenberg
    Swedish Inst Space Phys, Kiruna, Sweden..
    Wieser, Martin
    Swedish Inst Space Phys, Kiruna, Sweden..
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    The Influence of Spacecraft Charging on Low-Energy Ion Measurements Made by RPC-ICA on Rosetta2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 1, article id e2019JA027478Article in journal (Refereed)
    Abstract [en]

    Spacecraft charging is problematic for low-energy plasma measurements. The charged particles are attracted to or repelled from the charged spacecraft, affecting both the energy and direction of travel of the particles. The Ion Composition Analyzer (RPC-ICA) on board the Rosetta spacecraft is suffering from this effect. RPC-ICA was measuring positive ions in the vicinity of comet 67P/Churyumov-Gerasimenko, covering an energy range of a few eV/q to 40 keV/q. The low-energy part of the data is, however, heavily distorted by the negatively charged spacecraft. In this study we use the Spacecraft Plasma Interaction Software to model the influence of the spacecraft potential on the ion trajectories and the corresponding distortion of the field of view (FOV) of the instrument. The results show that the measurements are not significantly distorted when the ion energy corresponds to at least twice the spacecraft potential. Below this energy the FOV is often heavily distorted, but the distortion differs between different viewing directions. Generally, ions entering the instrument close to the aperture plane are less affected than those entering with extreme elevation angles. Plain Language Summary The Rosetta spacecraft followed comet 67P/Churyumov-Gerasimenko for 2 years, providing data giving new insights into the nature of comets. The Ion Composition Analyzer (RPC-ICA) on board the spacecraft measures positive ions in the vicinity of the comet. The instrument can measure low-energy ions, which play an important part in the processes taking place in this environment. To fully understand the environment around the comet, we have to understand these low-energy ions. Unfortunately, this part of the RPC-ICA data is distorted by the spacecraft potential. A spacecraft in space interacts with the surrounding environment, which charges the spacecraft surface to a positive or negative potential. Rosetta was commonly charged to a negative potential throughout the mission, which means that the positive ions measured by RPC-ICA were attracted to the spacecraft. Consequently, both the energy and the travel direction of the ions changed before detection. We investigate how the low-energy ions measured by RPC-ICA have been affected by the spacecraft potential. We use the Spacecraft Plasma Interaction Software to model these effects. The results give us a lower energy limit above which we can trust the measurements and show that some parts of the instrument are more heavily affected than others.

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    fulltext
  • 4.
    Bergman, Sofia
    et al.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.;Umeå Univ, Dept Phys, SE-90187 Umeå, Sweden..
    Wieser, Gabriella Stenberg
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Wieser, Martin
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Johansson, Fredrik Leffe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, Hans
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Nemeth, Zoltan
    Wigner Res Ctr Phys, Konkoly Thege M Rd 29-33, H-1121 Budapest, Hungary..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Williamson, Hayley
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Ion bulk speeds and temperatures in the diamagnetic cavity of comet 67P from RPC-ICA measurements2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 503, no 2, p. 2733-2745Article in journal (Refereed)
    Abstract [en]

    Y Comets are constantly interacting with the solar wind. When the comet activity is high enough, this leads to the creation of a magnetic field free region around the nucleus known as the diamagnetic cavity. It has been suggested that the ion-neutral drag force is balancing the magnetic pressure at the cavity boundary, but after the visit of Rosetta to comet 67P/Churyumov-Gerasimenko the coupling between ions and neutrals inside the cavity has been debated, at least for moderately active comets. In this study, we use data from the ion composition analyser to determine the bulk speeds and temperatures of the low-energy ions in the diamagnetic cavity of comet 67P. The low-energy ions are affected by the negative spacecraft potential, and we use the Spacecraft Plasma Interaction Software to model the resulting influence on the detected energy spectra. We find bulk speeds of 5-10 km s(-1) with a most probable speed of 7 km s(-1), significantly above the velocity of the neutral particles. This indicates that the collisional coupling between ions and neutrals is not strong enough to keep the ions at the same speed as the neutrals inside the cavity. The temperatures are in the range 0.7-1.6 eV, with a peak probability at 1.0 eV. We attribute the major part of the temperature to the fact that ions are born at different locations in the coma, and hence are accelerated over different distances before reaching the spacecraft.

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    fulltext
  • 5.
    Bernes, E.
    et al.
    Univ Trieste, Dept Chem & Pharmaceut Sci, I-34127 Trieste, Italy..
    Fronzoni, G.
    Univ Trieste, Dept Chem & Pharmaceut Sci, I-34127 Trieste, Italy..
    Stener, M.
    Univ Trieste, Dept Chem & Pharmaceut Sci, I-34127 Trieste, Italy..
    Guarnaccio, A.
    ISM CNR, Inst Struct Matter, Tito, PZ, Italy.;ISM CNR, Inst Struct Matter, Trieste, Italy..
    Zhang, T.
    Beijing Inst Technol BIT, Sch Informat & Elect, MIIT Key Lab Low Dimens Quantum Struct & Devices, Beijing 100081, Peoples R China.;Uppsala Univ, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Grazioli, C.
    IOM CNR, Lab TASC, Sincrotrone Trieste, I-34149 Trieste, Basovizza, Italy..
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Coreno, M.
    ISM CNR, Inst Struct Matter, Tito, PZ, Italy.;ISM CNR, Inst Struct Matter, Trieste, Italy..
    de Simone, M.
    IOM CNR, Lab TASC, Sincrotrone Trieste, I-34149 Trieste, Basovizza, Italy..
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Toffoli, D.
    Univ Trieste, Dept Chem & Pharmaceut Sci, I-34127 Trieste, Italy..
    S 2p and P 2p Core Level Spectroscopy of PPT Ambipolar Material and Its Building Block Moieties2020In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, no 127, p. 14510-14520Article in journal (Refereed)
    Abstract [en]

    The near-edge X-ray absorption fine structure (NEXAFS and X-ray photoelectron (XP) spectra of gas-phase 2,8-bis-(diphenylphosphoryl)dibenzo[b,d]thiophene (PPT) and triphenylphosphine oxide (TPPO) have been measured at the S and P L-II,L-III-edge regions. The time-dependent density functional theory (TDDFT) based on the relativistic two-component zeroth-order regular approximation approach has been used to provide an assignment of the experimental spectra, giving the contribution of the spin-orbit splitting and of the molecular-field splitting to the sulfur and phosphor binding energies. Computed XP and NEXAFS spectra agree well with the experimental measurements. In going from dibenzothiophene and TPPO to PPT, the nature of the most intense S 2p and P 2p NEXAFS features are preserved; this trend suggests that the electronic and geometric behaviors of the S and P atoms in the two building block moieties are conserved in the more complex system of PPT. This work enables us to shed some light onto the structure of the P-O bond, a still highly debated topic in the chemical literature. Since the S 2p and P 2p NEXAFS intensities provide specific information on the higher-lying localized sigma*(C-S) and sigma*(P-O) virtual MOs, we have concluded that P 3d AOs are not involved in the formation of the P-O bond. Moreover, the results support the mechanism of negative hyperconjugation, by showing that transitions toward sigma*(P-O) states occur at lower energies with respect to those toward it pi*(P-O) states.

  • 6.
    Breuillard, H.
    et al.
    Univ Orleans, CNES, CNRS, UMR7328,LPC2E, Orleans, France;Univ Paris Sud, Sorbonne Univ, Ecole Polytech, UMR7648 CNRS,Lab Phys Plasmas, Paris, France.
    Henri, P.
    Univ Orleans, CNES, CNRS, UMR7328,LPC2E, Orleans, France.
    Bucciantini, L.
    Univ Orleans, CNES, CNRS, UMR7328,LPC2E, Orleans, France.
    Volwerk, M.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Karlsson, T.
    KTH Royal Inst Technol, Stockholm, Sweden.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, E.
    Swedish Inst Space Phys, Uppsala, Sweden.
    Richter, I
    Tech Univ Carolo Wilhelmina Braunschweig, Braunschweig, Germany.
    Goetz, C.
    Tech Univ Carolo Wilhelmina Braunschweig, Braunschweig, Germany.
    Vallieres, X.
    Univ Orleans, CNES, CNRS, UMR7328,LPC2E, Orleans, France.
    Hajra, R.
    Univ Orleans, CNES, CNRS, UMR7328,LPC2E, Orleans, France;Natl Atmospher Res Lab, Tirupati, Andhra Pradesh, India.
    Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A39Article in journal (Refereed)
    Abstract [en]

    Using in situ measurements from different instruments on board the Rosetta spacecraft, we investigate the properties of the newly discovered low-frequency oscillations, known as singing comet waves, that sometimes dominate the close plasma environment of comet 67P/Churyumov-Gerasimenko. These waves are thought to be generated by a modified ion-Weibel instability that grows due to a beam of water ions created by water molecules that outgass from the comet. We take advantage of a cometary outburst event that occurred on 2016 February 19 to probe this generation mechanism. We analyze the 3D magnetic field waveforms to infer the properties of the magnetic oscillations of the cometary ion waves. They are observed in the typical frequency range (similar to 50 mHz) before the cometary outburst, but at similar to 20 mHz during the outburst. They are also observed to be elliptically right-hand polarized and to propagate rather closely (similar to 0-50 degrees) to the background magnetic field. We also construct a density dataset with a high enough time resolution that allows us to study the plasma contribution to the ion cometary waves. The correlation between plasma and magnetic field variations associated with the waves indicates that they are mostly in phase before and during the outburst, which means that they are compressional waves. We therefore show that the measurements from multiple instruments are consistent with the modified ion-Weibel instability as the source of the singing comet wave activity. We also argue that the observed frequency of the singing comet waves could be a way to indirectly probe the strength of neutral plasma coupling in the 67P environment.

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    FULLTEXT01
  • 7.
    Dreyer, Joshua
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    ESTEC, European Space Agency, Noordwijk, Netherlands.
    Hadid, Lina
    Laboratoire de Physique des Plasmas, Palaiseau, France.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Waite, J. Hunter
    Waite Science LLC, Pensacola, FL, USA.
    Electron to Light Ion Density Ratios during Cassini's Grand Finale: Addressing Open Questions About Saturn's Low-Latitude IonosphereManuscript (preprint) (Other academic)
  • 8.
    Dreyer, Joshua
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Shebanits, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Perryman, Rebecca S.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA..
    Waite, Jack Hunter
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA..
    Identifying Shadowing Signatures of C Ring Ringlets and Plateaus in Cassini Data from Saturn's Ionosphere2022In: The Planetary Science Journal, E-ISSN 2632-3338, Vol. 3, no 7, article id 168Article in journal (Refereed)
    Abstract [en]

    For orbits 288 and 292 of Cassini's Grand Finale, clear dips (sharp and narrow decreases) are visible in the H-2(+) densities measured by the Ion and Neutral Mass Spectrometer (INMS). In 2017, the southern hemisphere of Saturn was shadowed by its rings and the substructures within. Tracing a path of the solar photons through the ring plane to Cassini's position, we can identify regions in the ionosphere that were shadowed by the individual ringlets and plateaus (with increased optical depths) of Saturn's C ring. The calculated shadowed altitudes along Cassini's trajectory line up well with the dips in the H-2(+) data when adjusting the latter based on a detected evolving shift in the INMS timestamps since 2013, illustrating the potential for verification of instrument timings. We can further estimate the mean optical depths of the ringlets/plateaus by comparing the dips to inbound H-2(+) densities. Our results agree well with values derived from stellar occultation measurements. No clear dips are visible for orbits 283 and 287, whose periapsides were at higher altitudes. This can be attributed to the much longer chemical lifetime of H2+ at these higher altitudes, which in turn can be further used to estimate a lower limit for the flow speed along Cassini's trajectory. The resulting estimate of similar to 0.3 km s(-1) at an altitude of similar to 3400 km is in line with prior suggestions. Finally, the ringlet and plateau shadows are not associated with obvious dips in the electron density, which is expected due to their comparatively long chemical (recombination) lifetime.

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    fulltext
  • 9.
    Dreyer, Joshua
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Buchert, Stephan C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Waite, Jack Hunter
    Space Science and Engineering Division, Southwest Research Institute, San Antonio, USA .
    Constraining the Positive Ion Composition in Saturn's Lower Ionosphere with the Effective Recombination Coefficient2021In: The Planetary Science Journal, E-ISSN 2632-3338, Vol. 2, no 1, article id 39Article in journal (Refereed)
    Abstract [en]

    The present study combines Radio and Plasma Wave Science/Langmuir Probe and Ion and Neutral Mass Spectrometer data from Cassini's last four orbits into Saturn's lower ionosphere to constrain the effective recombination coefficient α300 from measured number densities and electron temperatures at a reference electron temperature of 300 K. Previous studies have shown an influx of ring material causes a state of electron depletion due to grain charging, which will subsequently affect the ionospheric chemistry. The requirement to take grain charging into account limits the derivation of α300 to upper limits. Assuming photochemical equilibrium and using an established method to calculate the electron production rate, we derive upper limits for α300 of ≲ 3 × 10−7 cm3 s−1 for altitudes below 2000 km. This suggests that Saturn's ionospheric positive ions are dominated by species with low recombination rate coefficients like HCO+. An ionosphere dominated by water group ions or complex hydrocarbons, as previously suggested, is incompatible with this result, as these species have recombination rate coefficients > 5 × 10−7 cm3 s−1 at an electron temperature of 300 K.

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    Dreyer_2021_Planet._Sci._J._2_39
  • 10.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Alho, M.
    Aalto Univ, Sch Elect Engn, Dept Radio Sci & Engn, POB 13000, FI-00076 Aalto, Finland..
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Behar, E.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Burch, J. L.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Carr, C. M.
    Imperial Coll London, Exhibit Rd, London SW7 2AZ, England..
    Cupido, E.
    Imperial Coll London, Exhibit Rd, London SW7 2AZ, England..
    Engelhardt, Ilka. A. D.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Glassmeier, K. -H
    Goetz, C.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Goldstein, R.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Henri, P.
    Lab Phys & Chim Environm & Espace, F-45071 Orleans 2, France..
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Koenders, C.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Mandt, K.
    Southwest Res Inst, 6220 Culebra Rd, San Antonio, TX 78238 USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX 78249 USA..
    Moestl, C.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Nilsson, H.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Wedlund, C. Simon
    Univ Oslo, Dept Phys, Box 1048 Blindern, N-0316 Oslo, Norway..
    Wieser, G. Stenberg
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Szego, K.
    Wigner Res Ctr Phys, Konkoly Thege Miklos Ut 29-33, H-1121 Budapest, Hungary..
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Volwerk, M.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    CME impact on comet 67P/Churyumov-Gerasimenko2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 462, p. S45-S56Article in journal (Refereed)
    Abstract [en]

    We present Rosetta observations from comet 67P/Churyumov-Gerasimenko during the impact of a coronal mass ejection (CME). The CME impacted on 2015 Oct 5-6, when Rosetta was about 800 km from the comet nucleus, and 1.4 au from the Sun. Upon impact, the plasma environment is compressed to the level that solar wind ions, not seen a few days earlier when at 1500 km, now reach Rosetta. In response to the compression, the flux of suprathermal electrons increases by a factor of 5-10 and the background magnetic field strength increases by a factor of similar to 2.5. The plasma density increases by a factor of 10 and reaches 600 cm(-3), due to increased particle impact ionization, charge exchange and the adiabatic compression of the plasma environment. We also observe unprecedentedly large magnetic field spikes at 800 km, reaching above 200 nT, which are interpreted as magnetic flux ropes. We suggest that these could possibly be formed by magnetic reconnection processes in the coma as the magnetic field across the CME changes polarity, or as a consequence of strong shears causing Kelvin-Helmholtz instabilities in the plasma flow. Due to the limited orbit of Rosetta, we are not able to observe if a tail disconnection occurs during the CME impact, which could be expected based on previous remote observations of other CME-comet interactions.

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  • 11.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    Lebreton, J. -P
    Gasc, S.
    Rubin, M.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gill, Reine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Erik P. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Carr, C. M.
    Cupido, E.
    Glassmeier, K. -H
    Goldstein, R.
    Koenders, C.
    Mandt, K.
    Nemeth, Z.
    Nilsson, H.
    Richter, I.
    Wieser, G. Stenberg
    Szego, K.
    Volwerk, M.
    Spatial distribution of low-energy plasma around comet 67P/CG from Rosetta measurements2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 11, p. 4263-4269Article in journal (Refereed)
    Abstract [en]

    We use measurements from the Rosetta plasma consortium Langmuir probe and mutual impedance probe to study the spatial distribution of low-energy plasma in the near-nucleus coma of comet 67P/Churyumov-Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e., the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be approximate to 1-210(-6), at a cometocentric distance of 10km and at 3.1AU from the Sun. A clear 6.2h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisionless plasma within 260km from the nucleus falls off with radial distance as approximate to 1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet.

  • 12.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, D. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Burch, J. L.
    SW Res Inst, San Antonio, TX USA..
    Carr, C. M.
    Univ London Imperial Coll Sci Technol & Med, Space & Atmospher Phys Grp, London, England..
    Cupido, E.
    Univ London Imperial Coll Sci Technol & Med, Space & Atmospher Phys Grp, London, England..
    Glassmeier, K. -H
    Goldstein, R.
    SW Res Inst, San Antonio, TX USA..
    Halekas, J. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Henri, P.
    Lab Phys & Chim Environm & Espace, Orleans, France..
    Koenders, C.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Mandt, K.
    SW Res Inst, San Antonio, TX USA..
    Mokashi, P.
    SW Res Inst, San Antonio, TX USA..
    Nemeth, Z.
    Wigner Res Ctr Phys, Budapest, Hungary..
    Nilsson, H.
    Swedish Inst Space Phys, S-98128 Kiruna, Sweden..
    Ramstad, R.
    Swedish Inst Space Phys, S-98128 Kiruna, Sweden..
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Wieser, G. Stenberg
    Swedish Inst Space Phys, S-98128 Kiruna, Sweden..
    Solar wind interaction with comet 67P: Impacts of corotating interaction regions2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 2, p. 949-965Article in journal (Refereed)
    Abstract [en]

    We present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) to comet 67P from October to December 2014. When the comet is 3.1-2.7AU from the Sun and the neutral outgassing rate approximate to 10(25)-10(26)s(-1), the CIRs significantly influence the cometary plasma environment at altitudes down to 10-30km. The ionospheric low-energy (approximate to 5eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below -20V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (approximate to 10-100eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2-5 as more interplanetary magnetic field piles up around the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events.

  • 13.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Goetz, Charlotte
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany.
    Nilsson, Hans
    Swedish Inst Space Phys, POB 812, SE-98128 Kiruna, Sweden;Lulea Univ Technol, Dept Comp Sci Elect & Space Engn, Rymdcampus 1, SE-98128 Kiruna, Sweden.
    Gilet, Nicolas
    CNRS, LPC2E, Orleans, France.
    Henri, Pierre
    CNRS, LPC2E, Orleans, France.
    The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P2019In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 158, no 2, article id 71Article in journal (Refereed)
    Abstract [en]

    We studied the distribution of cold electrons (<1 eV) around comet 67P/Churyumov-Gerasimenko with respect to the solar wind convective electric field direction. The cold plasma was measured by the Langmuir Probe instrument and the direction of the convective electric field E-conv = -nu x B was determined from magnetic field (B) measurements inside the coma combined with an assumption of a purely radial solar wind velocity nu. We found that the cold plasma is twice as likely to be observed when the convective electric field at Rosetta's position is directed toward the nucleus (in the -E(conv )hemisphere) compared to when it is away from the nucleus (in the +E-conv hemisphere). Similarly, the diamagnetic cavity, in which previous studies have shown that cold plasma is always present, was also found to be observed twice as often when in the -E-conv hemisphere, linking its existence circumstantially to the presence of cold electrons. The results are consistent with hybrid and Hall magnetohydrodynamic simulations as well as measurements of the ion distribution around the diamagnetic cavity.

  • 14.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hajra, R.
    CNRS, LPC2E, Orleans, France;Natl Atmospher Res Lab, Gadanki 517112, India.
    Henri, P.
    CNRS, LPC2E, Orleans, France.
    Wedlund, C. S.
    Univ Oslo, Dept Phys, Box 1048 Blindern, N-0316 Oslo, Norway.
    Alho, M.
    Aalto Univ, Sch Elect Engn, Dept Radio Sci & Engn, Aalto, Finland.
    Thiemann, E.
    Univ Colorado, Lab Atmospher & Space Phys, 3665 Discovery Dr, Boulder, CO 80303 USA.
    Solar flares observed by Rosetta at comet 67P/Churyumov-Gerasimenko2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A49Article in journal (Refereed)
    Abstract [en]

    Context. The Rosetta spacecraft made continuous measurements of the coma of comet 67P/Churyumov-Gerasimenko (67P) for more than two years. The plasma in the coma appeared very dynamic, and many factors control its variability. Aims. We wish to identify the effects of solar flares on the comet plasma and also their effect on the measurements by the Langmuir Probe Instrument (LAP). Methods. To identify the effects of flares, we proceeded from an existing flare catalog of Earth-directed solar flares, from which a new list was created that only included Rosetta-directed flares. We also used measurements of flares at Mars when at similar longitudes as Rosetta. The flare irradiance spectral model (FISM v.1) and its Mars equivalent (FISM-M) produce an extreme-ultraviolet (EUV) irradiance (10-120 nm) of the flares at 1 min resolution. LAP data and density measurements obtained with the Mutual Impedence Probe (MIP) from the time of arrival of the flares at Rosetta were examined to determine the flare effects. Results. From the vantage point of Earth, 1504 flares directed toward Rosetta occurred during the mission. In only 24 of these, that is, 1.6%, was the increase in EUV irradiance large enough to cause an observable effect in LAP data. Twenty-four Mars-directed flares were also observed in Rosetta data. The effect of the flares was to increase the photoelectron current by typically 1-5 nA. We find little evidence that the solar flares increase the plasma density, at least not above the background variability. Conclusions. Solar flares have a small effect on the photoelectron current of the LAP instrument, and they are not significant in comparison to other factors that control the plasma density in the coma. The photoelectron current can only be used for flare detection during periods of calm plasma conditions.

  • 15.
    Edberg, Niklas J. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    CNRS, Lab Phys & Chim Environm & Espace, Orleans, France.;UCA, Lab Lagrange, OCA, CNRS, Nice, France..
    De Keyser, J.
    BIRA IASB, Royal Belgian Inst Space Aeron, Brussels, Belgium..
    Radial distribution of plasma at comet 67P: Implications for cometary flyby missions2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 663, article id A42Article in journal (Refereed)
    Abstract [en]

    Context. The Rosetta spacecraft followed comet 67P/Churyumov-Gerasimenko (67P) for more than two years at a slow walking pace (similar to 1 m s(-1)) within 1500 km from the nucleus. During one of the radial movements of the spacecraft in the early phase of the mission, the radial distribution of the plasma density could be estimated, and the ionospheric density was found to be inversely proportional to the cometocentric distance r from the nucleus (a 1/r distribution). Aims. This study aims to further characterise the radial distribution of plasma around 67P throughout the mission and to expand on the initial results. We also aim to investigate how a 1/r distribution would be observed during a flyby with a fast (similar to 10's km s(-1)) spacecraft, such as the upcoming Comet Interceptor mission, when there is also an asymmetry introduced to the outgassing over the comet surface. Methods. To determine the radial distribution of the plasma, we used data from the Langmuir probe and Mutual Impedance instruments from the Rosetta Plasma Consortium during six intervals throughout the mission, for which the motion of Rosetta was approximately radial with respect to the comet. We then simulated what distribution a fast flyby mission would actually observe during its passage through a coma when there is a 1/r plasma density distribution as well as a sinusoidal variation with a phase angle (and then a sawtooth variation) multiplied to the outgassing rate. Results. The plasma density around comet 67P is found to roughly follow a 1/r dependence, although significant deviations occur in some intervals. If we normalise all data to a common outgassing rate (or heliocentric distance) and combine the intervals to a radial range of 10-1500 km, we find a 1/r(1.19) average distribution. The simulated observed density from a fast spacecraft flying through a coma with a 1/r distribution and an asymmetric outgassing can, in fact, appear anywhere in the range from a 1/r distribution to a 1/r(2) distribution, or even slightly outside of this range. Conclusions. The plasma density is distributed in such a way that it approximately decreases in a manner that is inversely proportional to the cometocentric distance. This is to be expected from the photoionisation of a collision-less, expanding neutral gas at a constant ionisation rate and expansion speed. The deviation from a pure 1/r distribution is in many cases caused by asymmetric outgassing over the surface, additional ionisation sources being present, electric fields accelerating plasma, and changing upstream solar wind conditions. A fast flyby mission can observe a radial distribution that deviates significantly from a 1/r trend if the outgassing is not symmetric over the surface. The altitude profile that will be observed depends very much on the level of outgassing asymmetry, the flyby velocity, the comet rotation rate, and the rotation phase. It is therefore essential to include data from both the inbound and outbound legs, as well as to compare plasma density to neutral density to get a more complete understanding of the radial distribution of the plasma.

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  • 16.
    Eriksson, Anders I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Engelhardt, Ilka. A. D.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Boström, Rolf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    LPC2E, Lab Phys & Chim Environm & Espace.
    Lebreton, J. -P
    LPC2E, Lab Phys & Chim Environm & Espace.
    Miloch, W. J.
    Univ Oslo, Dept Phys.
    Paulsson, J. J. P.
    Univ Oslo, Dept Phys.
    Wedlund, Cyril Simon
    Univ Oslo, Dept Phys.
    Yang, L.
    Univ Oslo, Dept Phys.
    Karlsson, T.
    Royal Inst Technol, Alfvén Lab.
    Jarvinen, R.
    Finnish Meteorol Inst, Helsinki 00560.
    Broiles, Thomas
    Southwest Res Inst, San Antonio.
    Mandt, K.
    Southwest Res Inst, San Antonio; Univ Texas San Antonio, Dept Phys & Astron.
    Carr, C. M.
    Imperial Coll London, Dept Phys.
    Galand, M.
    Imperial Coll London, Dept Phys.
    Nilsson, H.
    Swedish Inst Space Phys, S-98128 Kiruna.
    Norberg, C.
    Swedish Inst Space Phys, S-98128 Kiruna.
    Cold and warm electrons at comet 67P/Churyumov-Gerasimenko2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, article id A15Article in journal (Refereed)
    Abstract [en]

    Context. Strong electron cooling on the neutral gas in cometary comae has been predicted for a long time, but actual measurements of low electron temperature are scarce. Aims. Our aim is to demonstrate the existence of cold electrons in the inner coma of comet 67P/Churyumov-Gerasimenko and show filamentation of this plasma.

    Methods. In situ measurements of plasma density, electron temperature and spacecraft potential were carried out by the Rosetta Langmuir probe instrument, LAP. We also performed analytical modelling of the expanding two-temperature electron gas.

    Results. LAP data acquired within a few hundred km from the nucleus are dominated by a warm component with electron temperature typically 5-10 eV at all heliocentric distances covered (1.25 to 3.83 AU). A cold component, with temperature no higher than about 0.1 eV, appears in the data as short (few to few tens of seconds) pulses of high probe current, indicating local enhancement of plasma density as well as a decrease in electron temperature. These pulses first appeared around 3 AU and were seen for longer periods close to perihelion. The general pattern of pulse appearance follows that of neutral gas and plasma density. We have not identified any periods with only cold electrons present. The electron flux to Rosetta was always dominated by higher energies, driving the spacecraft potential to order -10 V.

    Conclusions. The warm (5-10 eV) electron population observed throughout the mission is interpreted as electrons retaining the energy they obtained when released in the ionisation process. The sometimes observed cold populations with electron temperatures below 0.1 eV verify collisional cooling in the coma. The cold electrons were only observed together with the warm population. The general appearance of the cold population appears to be consistent with a Haser-like model, implicitly supporting also the coupling of ions to the neutral gas. The expanding cold plasma is unstable, forming filaments that we observe as pulses.

  • 17.
    Galand, M.
    et al.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Heritier, K. L.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    Univ Orleans, CNRS, LPC2E, 3A,Ave Rech Sci, F-45071 Orleans 2, France..
    Broiles, T. W.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Allen, A. J.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Altwegg, K.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Beth, A.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Burch, J. L.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Carr, C. M.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Cupido, E.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Glassmeier, K. -H
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lebreton, J. -P
    Mandt, K. E.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Nilsson, H.
    Swedish Inst Space Phys, POB 812, SE-98128 Kiruna, Sweden..
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Rubin, M.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Sagnieres, L. B. M.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Schwartz, S. J.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England..
    Semon, T.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Tzou, C. -Y
    Vallieres, X.
    Univ Orleans, CNRS, LPC2E, 3A,Ave Rech Sci, F-45071 Orleans 2, France..
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wurz, P.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Ionospheric plasma of comet 67P probed by Rosetta at 3 au from the Sun2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 462, p. S331-S351Article in journal (Refereed)
    Abstract [en]

    We propose to identify the main sources of ionization of the plasma in the coma of comet 67P/Churyumov-Gerasimenko at different locations in the coma and to quantify their relative importance, for the first time, for close cometocentric distances (< 20 km) and large heliocentric distances (> 3 au). The ionospheric model proposed is used as an organizing element of a multi-instrument data set from the Rosetta Plasma Consortium (RPC) plasma and particle sensors, from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis and from the Microwave Instrument on the Rosetta Orbiter, all on board the ESA/Rosetta spacecraft. The calculated ionospheric density driven by Rosetta observations is compared to the RPC-Langmuir Probe and RPC-Mutual Impedance Probe electron density. The main cometary plasma sources identified are photoionization of solar extreme ultraviolet (EUV) radiation and energetic electron-impact ionization. Over the northern, summer hemisphere, the solar EUV radiation is found to drive the electron density - with occasional periods when energetic electrons are also significant. Over the southern, winter hemisphere, photoionization alone cannot explain the observed electron density, which reaches sometimes higher values than over the summer hemisphere; electron-impact ionization has to be taken into account. The bulk of the electron population is warm with temperature of the order of 7-10 eV. For increased neutral densities, we show evidence of partial energy degradation of the hot electron energy tail and cooling of the full electron population.

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  • 18.
    Gilet, N.
    et al.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France..
    Henri, P.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France.;Lab Lagrange, CNRS, UCA, OCA, Nice, France..
    Wattieaux, G.
    Univ Toulouse, LAPLACE UMR 5213, F-31062 Toulouse, France..
    Traore, N.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vallieres, X.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France..
    More, J.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France..
    Randriamboarison, O.
    Univ Orleans, Lab Phys & Chim Environm & Espace LPC2E, CNRS, Orleans, France..
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Swedish Inst Space Phys, Box 537, S-75121 Uppsala, Sweden.;Uppsala Univ, Dept Phys & Astron, Box 516, S-75210 Uppsala, Sweden..
    Rubin, M.
    Univ Bern, Phys Inst, Sidelerstr 5, CH-3012 Bern, Switzerland..
    Observations of a mix of cold and warm electrons by RPC-MIP at 67P/Churyumov-Gerasimenko2020In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 640, article id A110Article in journal (Refereed)
    Abstract [en]

    Context. The Mutual Impedance Probe (MIP) of the Rosetta Plasma Consortium (RPC) onboard the Rosetta orbiter which was in operation for more than two years, between August 2014 and September 2016 to monitor the electron density in the cometary ionosphere of 67P/Churyumov-Gerasimenko. Based on the resonance principle of the plasma eigenmodes, recent models of the mutual impedance experiment have shown that in a two-electron temperature plasma, such an instrument is able to separate the two isotropic electron populations and retrieve their properties.Aims. The goal of this paper is to identify and characterize regions of the cometary ionized environment filled with a mix of cold and warm electron populations, which was observed by Rosetta during the cometary operation phase.Methods. To reach this goal, this study identifies and investigates the in situ mutual impedance spectra dataset of the RPC-MIP instrument that contains the characteristics of a mix of cold and warm electrons, with a special focus on instrumental signatures typical of large cold-to-total electron density ratio (from 60 to 90%), that is, regions strongly dominated by the cold electron component.Results. We show from the observational signatures that the mix of cold and warm cometary electrons strongly depends on the cometary latitude. Indeed, in the southern hemisphere of 67P, where the neutral outgassing activity was higher than in northern hemisphere during post-perihelion, the cold electrons were more abundant, confirming the role of electron-neutral collisions in the cooling of cometary electrons. We also show that the cold electrons are mainly observed outside the nominal electron-neutral collision-dominated region (exobase), where electrons are expected to have cooled down. This which indicates that the cold electrons have been transported outward. Finally, RPC-MIP detected cold electrons far from the perihelion, where the neutral outgassing activity is lower, in regions where no electron exobase was expected to have formed. This suggests that the cometary neutrals provide a more frequent or efficient cooling of the electrons than expected for a radially expanding ionosphere.

  • 19.
    Gunell, Herbert
    et al.
    Umeå Univ, Dept Phys, S-90187 Umeå, Sweden..
    Goetz, Charlotte
    European Space Agcy, Space Res & Technol Ctr, Keplerlaan 1, NL-2201 AZ Noordwijk, Netherlands..
    Odelstad, Elias
    Royal Inst Technol, Dept Space & Plasma Phys, S-10044 Stockholm, Sweden..
    Beth, Arnaud
    Umeå Univ, Dept Phys, S-90187 Umeå, Sweden..
    Hamrin, Maria
    Umeå Univ, Dept Phys, S-90187 Umeå, Sweden..
    Henri, Pierre
    CNRS, LPC2E, F-45071 Orleans, France.;UCA, CNRS, OCA, Lagrange, Nice, France..
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Swedish Inst Space Phys, Box 537, S-75121 Uppsala, Sweden..
    Nilsson, Hans
    Swedish Inst Space Phys, Box 812, S-98128 Kiruna, Sweden..
    Wieser, Gabriella Stenberg
    Swedish Inst Space Phys, Box 812, S-98128 Kiruna, Sweden..
    Ion acoustic waves near a comet nucleus: Rosetta observations at comet 67P/Churyumov-Gerasimenko2021In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 39, no 1, p. 53-68Article in journal (Refereed)
    Abstract [en]

    Ion acoustic waves were observed between 15 and 30 km from the centre of comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft during its close flyby on 28 March 2015. There are two electron populations: one cold at k(B)T(e) approximate to 0.2 eV and one warm at k(B)T(e) approximate to 2 eV. The ions are dominated by a cold (a few hundredths of electronvolt) distribution of water group ions with a bulk speed of (3-3.7) km s(-1). A warm k(B)T(e) approximate to 6 eV ion population, which also is present, has no influence on the ion acoustic waves due to its low density of only 0.25 % of the plasma density. Near closest approach the propagation direction was within 50 degrees from the direction of the bulk velocity. The waves, which in the plasma frame appear below the ion plasma frequency f(pi) approximate to 2 kHz, are Doppler-shifted to the spacecraft frame where they cover a frequency range up to approximately 4 kHz. The waves are detected in a region of space where the magnetic field is piled up and draped around the inner part of the ionised coma. Estimates of the current associated with the magnetic field gradient as observed by Rosetta are used as input to calculations of dispersion relations for current-driven ion acoustic waves, using kinetic theory. Agreement between theory and observations is obtained for electron and ion distributions with the properties described above. The wave power decreases over cometocentric distances from 24 to 30 km. The main difference between the plasma at closest approach and in the region where the waves are decaying is the absence of a significant current in the latter. Wave observations and theory combined supplement the particle measurements that are difficult at low energies and complicated by spacecraft charging.

  • 20.
    Heritier, K. L.
    et al.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
    Altwegg, K.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland.
    Berthelier, J. -J
    Beth, A.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
    Carr, C. M.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
    De Keyser, J.
    Royal Belgian Inst Space Aeron, BIRA IASB, Ringlaan 3, Brussels, Belgium.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fuselier, S. A.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA;Univ Texas San Antonio, San Antonio, TX 78249 USA.
    Galand, M.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
    Gombosi, T. I.
    Univ Michigan, Dept Atmospher Ocean & Space Sci, Ann Arbor, MI 48109 USA.
    Henri, P.
    CNRS, LPC2E, 3 Ave Rech Sci, F-45071 Orleans, France.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, H.
    Swedish Inst Space Phys, POB 812, S-98128 Kiruna, Sweden.
    Rubin, M.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland.
    Wedlund, C. Simon
    Univ Oslo, Dept Phys, Sem Saelands Vei 24Postbox 1048, N-0317 Oslo, Norway.
    Taylor, M. G. G. T.
    European Space Agcy, Estec, Keplerlaan 1, NL-2200 AG Noordwijk, Netherlands.
    Vigren, E.
    LATMOS IPSL CNRS UPMC UVSQ, F-94100 St Maur, France.
    On the origin of molecular oxygen in cometary comae2018In: Nature Communications, E-ISSN 2041-1723, Vol. 9, article id 2580Article in journal (Other academic)
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  • 21.
    Heritier, K. L.
    et al.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
    Galand, M.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
    Henri, P.
    Univ Orleans, CNRS, LPC2E, F-45100 Orleans, France.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Beth, A.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vallieres, X.
    Univ Orleans, CNRS, LPC2E, F-45100 Orleans, France.
    Altwegg, K.
    Univ Bern, Inst Phys, Sidlerstr 5, CH-3012 Bern, Switzerland.
    Burch, J. L.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA.
    Carr, C.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
    Ducrot, E.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England;Univ Liege, Space Sci Technol & Astrophys Res STAR Inst, B-4000 Liege, Belgium.
    Hajra, R.
    Univ Orleans, CNRS, LPC2E, F-45100 Orleans, France.
    Rubin, M.
    Univ Bern, Inst Phys, Sidlerstr 5, CH-3012 Bern, Switzerland.
    Plasma source and loss at comet 67P during the Rosetta mission2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 618, article id A77Article in journal (Refereed)
    Abstract [en]

    Context. The Rosetta spacecraft provided us with a unique opportunity to study comet 67P/Churyumov-Gerasimenko (67P) from a close perspective and over a 2-yr time period. Comet 67P is a weakly active comet. It was therefore unexpected to find an active and dynamic ionosphere where the cometary ions were largely dominant over the solar wind ions, even at large heliocentric distances. Aims. Our goal is to understand the different drivers of the cometary ionosphere and assess their variability over time and over the different conditions encountered by the comet during the Rosetta mission. Methods. We used a multi-instrument data-based ionospheric model to compute the total ion number density at the position of Rosetta. In-situ measurements from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) and the Rosetta Plasma Consortium (RPC)-Ion and Electron Sensor (IES), together with the RPC-LAngmuir Probe instrument (LAP) were used to compute the local ion total number density. The results are compared to the electron densities measured by RPC-Mutual Impedance Probe (MIP) and RPC-LAP. Results. We were able to disentangle the physical processes responsible for the formation of the cometary ions throughout the 2-yr escort phase and we evaluated their respective magnitudes. The main processes are photo-ionization and electron-impact ionization. The latter is a significant source of ionization at large heliocentric distance (>2 au) and was predominant during the last 4 months of the mission. The ionosphere was occasionally subject to singular solar events, temporarily increasing the ambient energetic electron population. Solar photons were the main ionizer near perihelion at 1.3 au from the Sun, during summer 2015.

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  • 22.
    Johansson, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Swedish Inst Space Phys, Uppsala, Sweden.;Uppsala Univ, Dept Astron & Space Phys, Uppsala, Sweden..
    Eriksson, A. I.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Vigren, E.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Bucciantini, L.
    CNRS, Lab Phys & Chim Environm & Espace, Orleans, France..
    Henri, P.
    CNRS, Lab Phys & Chim Environm & Espace, Orleans, France.;UCA, CNRS, Lab Lagrange, OCA, Nice, France..
    Nilsson, H.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Bergman, S.
    Swedish Inst Space Phys, Kiruna, Sweden.;Umeå Univ, Dept Phys, Umeå, Sweden..
    Edberg, N. J. T.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Stenberg Wieser, G.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Odelstad, E.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Plasma densities, flow, and solar EUV flux at comet 67P A cross-calibration approach2021In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 653, article id A128Article in journal (Refereed)
    Abstract [en]

    Context. During its two-year mission at comet 67P, Rosetta nearly continuously monitored the inner coma plasma environment for gas production rates varying over three orders of magnitude, at distances to the nucleus ranging from a few to a few hundred kilometres. To achieve the best possible measurements, cross-calibration of the plasma instruments is needed. Aims. Our goal is to provide a consistent plasma density dataset for the full mission, while in the process providing a statistical characterisation of the plasma in the inner coma and its evolution. Methods. We constructed physical models for two different methods to cross-calibrate the spacecraft potential and the ion current as measured by the Rosetta Langmuir probes (LAP) to the electron density as measured by the Mutual Impedance Probe (MIP). We also described the methods used to estimate spacecraft potential, and validated the results with the Ion Composition Analyser (ICA). Results. We retrieve a continuous plasma density dataset for the entire cometary mission with a much improved dynamical range compared to any plasma instrument alone and, at times, improve the temporal resolution from 0.24-0.74 Hz to 57.8 Hz. The physical model also yields, at a three-hour time resolution, ion flow speeds and a proxy for the solar EUV flux from the photoemission from the Langmuir probes. Conclusions. We report on two independent mission-wide estimates of the ion flow speed that are consistent with the bulk H2O+ ion velocities as measured by the ICA. We find the ion flow to consistently be much faster than the neutral gas over the entire mission, lending further evidence that the ions are collisionally decoupled from the neutrals in the coma. Measurements of ion speeds from Rosetta are therefore not consistent with the assumptions made in previously published plasma density models of the comet 67P's ionosphere at the start and end of the mission. Also, the measured EUV flux is perfectly consistent with independently derived values previously published from LAP and lends support for the conclusions drawn regarding an attenuation of solar EUV from a distant nanograin dust population, when the comet activity was high. The new density dataset is consistent with the existing MIP density dataset, but it facilitates plasma analysis on much shorter timescales, and it also covers long time periods where densities were too low to be measured by MIP.

  • 23.
    Johansson, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Swedish Inst Space Phys, Uppsala, Sweden.;Uppsala Univ, Dept Astron & Space Phys, Uppsala, Sweden..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Gilet, N.
    CNRS, Lab Phys & Chim Environm & Espace, Orleans, France..
    Henri, P.
    CNRS, Lab Phys & Chim Environm & Espace, Orleans, France.;UCA, CNRS, Lab Lagrange, OCA, Nice, France..
    Wattieaux, G.
    Univ Paul Sabatier Toulouse III, Toulouse, France..
    Taylor, M. G. G. T.
    ESA ESTEC, Noordwijk, Netherlands..
    Imhof, C.
    Airbus Def & Space GmbH, Friedrichshafen, Germany..
    Cipriani, F.
    ESA ESTEC, Noordwijk, Netherlands..
    A charging model for the Rosetta spacecraft2020In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 642, article id A43Article in journal (Refereed)
    Abstract [en]

    Context. The electrostatic potential of a spacecraft, V-S, is important for the capabilities of in situ plasma measurements. Rosetta has been found to be negatively charged during most of the comet mission and even more so in denser plasmas.Aims. Our goal is to investigate how the negative V-S correlates with electron density and temperature and to understand the physics of the observed correlation.Methods. We applied full mission comparative statistics of V-S, electron temperature, and electron density to establish V-S dependence on cold and warm plasma density and electron temperature. We also used Spacecraft-Plasma Interaction System (SPIS) simulations and an analytical vacuum model to investigate if positively biased elements covering a fraction of the solar array surface can explain the observed correlations.Results. Here, the V-S was found to depend more on electron density, particularly with regard to the cold part of the electrons, and less on electron temperature than was expected for the high flux of thermal (cometary) ionospheric electrons. This behaviour was reproduced by an analytical model which is consistent with numerical simulations.Conclusions. Rosetta is negatively driven mainly by positively biased elements on the borders of the front side of the solar panels as these can efficiently collect cold plasma electrons. Biased elements distributed elsewhere on the front side of the panels are less efficient at collecting electrons apart from locally produced electrons (photoelectrons). To avoid significant charging, future spacecraft may minimise the area of exposed bias conductors or use a positive ground power system.

  • 24.
    Johansson, Fredrik L.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Paulsson, J. J. P.
    Univ Oslo, Dept Phys, Sem Saelands Vei 24,Postbox 1048, N-0317 Oslo, Norway.
    Harang, S. S.
    Univ Oslo, Dept Phys, Sem Saelands Vei 24,Postbox 1048, N-0317 Oslo, Norway.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Mannel, T.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria;Karl Franzens Univ Graz, Phys Inst, Univ Pl 5, A-8010 Graz, Austria.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Miloch, W. J.
    Univ Oslo, Dept Phys, Sem Saelands Vei 24,Postbox 1048, N-0317 Oslo, Norway.
    Wedlund, C. Simon
    Univ Oslo, Dept Phys, Sem Saelands Vei 24,Postbox 1048, N-0317 Oslo, Norway.
    Thiemann, E.
    Univ Colorado, Lab Atmospher & Space Phys, 3665 Discovery Dr, Boulder, CO 80303 USA.
    Eparvier, F.
    Univ Colorado, Lab Atmospher & Space Phys, 3665 Discovery Dr, Boulder, CO 80303 USA.
    Andersson, L.
    Univ Colorado, Lab Atmospher & Space Phys, 3665 Discovery Dr, Boulder, CO 80303 USA.
    Rosetta photoelectron emission and solar ultraviolet flux at comet 67P2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S626-S635Article in journal (Refereed)
    Abstract [en]

    The Langmuir Probe instrument on Rosetta monitored the photoelectron emission current of the probes during the Rosetta mission at comet 67P/Churyumov-Gerasimenko, in essence acting as a photodiode monitoring the solar ultraviolet radiation at wavelengths below 250 nm. We have used three methods of extracting the photoelectron saturation current from the Langmuir probe measurements. The resulting data set can be used as an index of the solar far and extreme ultraviolet at the Rosetta spacecraft position, including flares, in wavelengths which are important for photoionization of the cometary neutral gas. Comparing the photoemission current to data measurements by MAVEN/EUVM and TIMED/SEE, we find good correlation when 67P was at large heliocentric distances early and late in the mission, but up to 50 per cent decrease of the expected photoelectron current at perihelion. We discuss possible reasons for the photoemission decrease, including scattering and absorption by nanograins created by disintegration of cometary dust far away from the nucleus.

  • 25.
    Johansson, Fredrik Leffe
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Rosetta Observations of Plasma and Dust at Comet 67P2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In-situ observations of cometary plasma are not made because they are easy. The historic ESA Rosetta mission was launched in 2004 and traversed space for ten years before arriving at comet 67P/Churyumov-Gerasimenko, which it studied in unprecedented detail for two years. For the Rosetta Dual Langmuir Probe Experiment (LAP), the challenge was increased by the sensors being situated on short booms near a significantly negatively charged spacecraft, which deflects low-energy charged particles away from our instrument. To disentangle the cometary plasma signature in our signal, we create a charging model for the particular design of the Rosetta spacecraft through 3D Particle-in-Cell/hybrid spacecraft-plasma interaction simulations, which also can be applicable to similarly designed spacecraft in cold plasma environments. By virtue of this model, we find a way to cross-calibrate (with the Mutual Impedance probe, MIP) the LAP spacecraft potential to a plasma density estimate with increased temporal resolution and dynamic range than any single plasma instrument alone.

    To characterise and disentangle the Sun-driven photoelectric current from the positive cometary ion current signal, using three different methods (where we believe one is novel), we find a signature of an attenuation of the Extreme Ultraviolet (EUV) radiation from the Sun that follows the cometary out-gassing activity. We discuss possible reasons for this, where the scattering and absorption of radiation by ~20 nm sized dust grains created by the disintegration of far larger cometary dust grains far from the nucleus appears most likely.

    By cross-calibrating also our current measurements to MIP, we find a cometary ion speed estimate, which, when applied to a simple comet ionosphere model using the LAP photoemission as a photoionisation proxy, predicts the measured comet plasma densities near perihelion, when comet activity was highest. This demonstrates that the LAP cross-calibration estimates are self-consistent, but also strongly suggests that the EUV attenuation we reported is apparent also in the comet ionosphere, as less plasma is ionised by EUV radiation. The ion speed estimates from LAP are consistent with recent results of cometary water ion velocities from the Ion Composition Analyser (ICA), and much elevated above the comet neutral speed, often by a factor of 5. This verifies that the cometary ions are not collisionally coupled to the neutrals, and instead rapidly accelerated by some electric field, such as an ambipolar electric field or from plasma wave activity.

    List of papers
    1. Rosetta photoelectron emission and solar ultraviolet flux at comet 67P
    Open this publication in new window or tab >>Rosetta photoelectron emission and solar ultraviolet flux at comet 67P
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    2017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S626-S635Article in journal (Refereed) Published
    Abstract [en]

    The Langmuir Probe instrument on Rosetta monitored the photoelectron emission current of the probes during the Rosetta mission at comet 67P/Churyumov-Gerasimenko, in essence acting as a photodiode monitoring the solar ultraviolet radiation at wavelengths below 250 nm. We have used three methods of extracting the photoelectron saturation current from the Langmuir probe measurements. The resulting data set can be used as an index of the solar far and extreme ultraviolet at the Rosetta spacecraft position, including flares, in wavelengths which are important for photoionization of the cometary neutral gas. Comparing the photoemission current to data measurements by MAVEN/EUVM and TIMED/SEE, we find good correlation when 67P was at large heliocentric distances early and late in the mission, but up to 50 per cent decrease of the expected photoelectron current at perihelion. We discuss possible reasons for the photoemission decrease, including scattering and absorption by nanograins created by disintegration of cometary dust far away from the nucleus.

    Place, publisher, year, edition, pages
    OXFORD UNIV PRESS, 2017
    Keywords
    plasmas, methods: data analysis, Sun: UV radiation, comets: individual: 67P/Churyumov-Gerasimenko, dust, extinction
    National Category
    Astronomy, Astrophysics and Cosmology
    Identifiers
    urn:nbn:se:uu:diva-376695 (URN)10.1093/mnras/stx2369 (DOI)000443940500056 ()
    Conference
    International Conference on Cometary Science - Comets - A New Vision after Rosetta and Philae, NOV 14-18, 2016, Toulouse, FRANCE
    Available from: 2019-02-08 Created: 2019-02-08 Last updated: 2020-11-23Bibliographically approved
    2. A charging model for the Rosetta spacecraft
    Open this publication in new window or tab >>A charging model for the Rosetta spacecraft
    Show others...
    2020 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 642, article id A43Article in journal (Refereed) Published
    Abstract [en]

    Context. The electrostatic potential of a spacecraft, V-S, is important for the capabilities of in situ plasma measurements. Rosetta has been found to be negatively charged during most of the comet mission and even more so in denser plasmas.Aims. Our goal is to investigate how the negative V-S correlates with electron density and temperature and to understand the physics of the observed correlation.Methods. We applied full mission comparative statistics of V-S, electron temperature, and electron density to establish V-S dependence on cold and warm plasma density and electron temperature. We also used Spacecraft-Plasma Interaction System (SPIS) simulations and an analytical vacuum model to investigate if positively biased elements covering a fraction of the solar array surface can explain the observed correlations.Results. Here, the V-S was found to depend more on electron density, particularly with regard to the cold part of the electrons, and less on electron temperature than was expected for the high flux of thermal (cometary) ionospheric electrons. This behaviour was reproduced by an analytical model which is consistent with numerical simulations.Conclusions. Rosetta is negatively driven mainly by positively biased elements on the borders of the front side of the solar panels as these can efficiently collect cold plasma electrons. Biased elements distributed elsewhere on the front side of the panels are less efficient at collecting electrons apart from locally produced electrons (photoelectrons). To avoid significant charging, future spacecraft may minimise the area of exposed bias conductors or use a positive ground power system.

    Place, publisher, year, edition, pages
    EDP SCIENCES S A, 2020
    Keywords
    plasmas, comets: individual: 67P, Churyumov-Gerasimenko, methods: numerical, methods: data analysis, space vehicles
    National Category
    Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
    Identifiers
    urn:nbn:se:uu:diva-423927 (URN)10.1051/0004-6361/202038592 (DOI)000577102500005 ()
    Funder
    Swedish National Space Board, 168/15
    Available from: 2020-10-30 Created: 2020-10-30 Last updated: 2020-11-23Bibliographically approved
    3. Plasma densitites, flow and Solar EUV flux at comet 67P: A cross-calibration approach
    Open this publication in new window or tab >>Plasma densitites, flow and Solar EUV flux at comet 67P: A cross-calibration approach
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    (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed) Submitted
    Abstract [en]

    Context.During its two year mission at comet 67P, Rosetta nearly continuously monitored the inner coma plasma environment forgas production rates varying over three orders of magnitude, at distances to the nucleus from a few to a few hundred km. To achievethe best possible measurements, cross-calibration of the plasma instruments is needed.Aims.To provide a consistent plasma density data set for the full mission, in the process providing a statistical characterisation of theplasma processes in the inner coma and their evolution.Methods.We construct physical models for two different methods to cross-calibrate the spacecraft potential and the ion current asmeasured by the Rosetta Langmuir Probes (LAP) to the electron density as measured by the Mutual Impedance Probe (MIP). We alsodescribe the methods used to estimate spacecraft potential, and validate the results with the Ion Composition Analyser, (ICA).Results.We retrieve a continuous plasma density dataset for the entire cometary mission with a much improved dynamical rangecompared to any plasma instrument alone and, at times, improve the temporal resolution from 0.24-0.74 Hz to 57.8 Hz. The physicalmodel also yields, at 3 hour time resolution, ion flow speeds as well as a proxy for the solar EUV flux from the photoemission fromthe Langmuir Probes.Conclusions.We report on two independent estimates of the ion flow speed which are consistent with the bulk H2O+ion velocitiesas measured by ICA. We find the ion flow to be much faster than the neutral gas, lending further evidence that the ions are mostlycollisionally decoupled from the neutrals in the coma. Also, the measured EUV flux is perfectly consistent with independent measurements previously published in Johansson et al. (2017) and lends support for the conclusions drawn therein regarding an attenuationof solar EUV from a distant nanograin dust population between the comet and the Sun, when the comet activity was high. The newdensity dataset is consistent with the existing MIP density dataset, but facilitates plasma analysis at much shorter timescales, with anincreased temporal resolution of a factor of (up to) 240 and covers also long time periods where densities were too low to be measuredby MIP.

    Keywords
    plasmas, comets, comet 67P/Churyumov-Gerasimenko, Langmuir Probes
    National Category
    Fusion, Plasma and Space Physics
    Research subject
    Physics with specialization in Space and Plasma Physics
    Identifiers
    urn:nbn:se:uu:diva-425952 (URN)
    Funder
    Swedish National Space Board, 168/15
    Available from: 2020-11-22 Created: 2020-11-22 Last updated: 2020-11-23
    4. Ionisation and EUV attenuation at comet 67P
    Open this publication in new window or tab >>Ionisation and EUV attenuation at comet 67P
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    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Context. The new cross-calibrated density dataset from the Rosetta Plasma Consortium (RPC) is ideal for investigating the comet 67P/Churyumov-Gerasimenko ionosphere and its long-term evolution as the gas production rate varied over three orders of magnitude. Although event-based studies have, at times, shown the importance of 20-200 eV electrons for the ionisation of the cometary gas, mission-wide statistics have not been made before. 

    Aims. We attempt to build on previous successful modelling efforts (with good accuracy, but poor precision) at selected events to obtain a more generalised understanding, also encompassing the peak activity near perihelion.Methods. Using the neutral gas production as measured by ROSINA/COPS, in conjunction with recent findings on the bulk cometary ion flow, as well as estimates of photoionisation and electron-impact ionisation from RPC instruments, we construct an ionosphere model and compare it to the new cross-calibrated electron density dataset

    Results. We find that the photoionisation and elevated ion flow speeds as measured by LAP produce self-consistent densities in a simple cometary ionosphere model based on the cross-calibrated density dataset. The ion velocities are also consistent with the radial ICA ion bulk flows, and are a factor of five times larger than the neutral speeds. Also, the consistent photoionisation estimate lends further evidence that the solar EUV is attenuated everywhere in the cometary ionosphere at peak activities. We also find that electron-impact ionisation seems to increase with decreasing cometocentric distance. This points towards an external source of hot electrons that are accelerated by a (generally radial) ambipolar electric field, which also have been hypothesised to be the mechanism behind the elevated ion speeds.

    Conclusions. The cometary ionospheric densities as measured by Rosetta is consistent with a model where an ambipolar electric field strongly affects the distribution of the plasma, and collisions play only a minor role. The attenuation of the EUV in the cometary ionosphere reported cannot be local, and is only readily explained by a significant population of nanodust, produced beyond 2000 km in the comet-sun direction via erosion or fragmentation of larger grains.

    Keywords
    plasmas, comets, comet 67P/Churyumov-Gerasimenko
    National Category
    Fusion, Plasma and Space Physics
    Research subject
    Physics with specialization in Space and Plasma Physics
    Identifiers
    urn:nbn:se:uu:diva-425951 (URN)
    Funder
    Swedish National Space Board, 168/15
    Available from: 2020-11-22 Created: 2020-11-22 Last updated: 2020-11-23
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  • 26.
    Johansson, Fredrik Leffe
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Bucciantini, Luca
    LPC2E, CNRS, Orléans, France.
    Henri, Pierre
    LPC2E, CNRS, Orléans France.
    Nilsson, Hans
    Swedish Institute of Space Physics.
    Bergman, Sofia
    Swedish Institute of Space Physics.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Stenberg Wieser, Gabriella
    Swedish Institute of Space Physics.
    Odelstad, Elias
    KTH, SPP Space and Plasma Physics.
    Plasma densitites, flow and Solar EUV flux at comet 67P: A cross-calibration approachIn: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed)
    Abstract [en]

    Context.During its two year mission at comet 67P, Rosetta nearly continuously monitored the inner coma plasma environment forgas production rates varying over three orders of magnitude, at distances to the nucleus from a few to a few hundred km. To achievethe best possible measurements, cross-calibration of the plasma instruments is needed.Aims.To provide a consistent plasma density data set for the full mission, in the process providing a statistical characterisation of theplasma processes in the inner coma and their evolution.Methods.We construct physical models for two different methods to cross-calibrate the spacecraft potential and the ion current asmeasured by the Rosetta Langmuir Probes (LAP) to the electron density as measured by the Mutual Impedance Probe (MIP). We alsodescribe the methods used to estimate spacecraft potential, and validate the results with the Ion Composition Analyser, (ICA).Results.We retrieve a continuous plasma density dataset for the entire cometary mission with a much improved dynamical rangecompared to any plasma instrument alone and, at times, improve the temporal resolution from 0.24-0.74 Hz to 57.8 Hz. The physicalmodel also yields, at 3 hour time resolution, ion flow speeds as well as a proxy for the solar EUV flux from the photoemission fromthe Langmuir Probes.Conclusions.We report on two independent estimates of the ion flow speed which are consistent with the bulk H2O+ion velocitiesas measured by ICA. We find the ion flow to be much faster than the neutral gas, lending further evidence that the ions are mostlycollisionally decoupled from the neutrals in the coma. Also, the measured EUV flux is perfectly consistent with independent measurements previously published in Johansson et al. (2017) and lends support for the conclusions drawn therein regarding an attenuationof solar EUV from a distant nanograin dust population between the comet and the Sun, when the comet activity was high. The newdensity dataset is consistent with the existing MIP density dataset, but facilitates plasma analysis at much shorter timescales, with anincreased temporal resolution of a factor of (up to) 240 and covers also long time periods where densities were too low to be measuredby MIP.

  • 27.
    Johansson, Fredrik Leffe
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Stephenson, Peter
    Imperial College London, London UK.
    Ionisation and EUV attenuation at comet 67PManuscript (preprint) (Other academic)
    Abstract [en]

    Context. The new cross-calibrated density dataset from the Rosetta Plasma Consortium (RPC) is ideal for investigating the comet 67P/Churyumov-Gerasimenko ionosphere and its long-term evolution as the gas production rate varied over three orders of magnitude. Although event-based studies have, at times, shown the importance of 20-200 eV electrons for the ionisation of the cometary gas, mission-wide statistics have not been made before. 

    Aims. We attempt to build on previous successful modelling efforts (with good accuracy, but poor precision) at selected events to obtain a more generalised understanding, also encompassing the peak activity near perihelion.Methods. Using the neutral gas production as measured by ROSINA/COPS, in conjunction with recent findings on the bulk cometary ion flow, as well as estimates of photoionisation and electron-impact ionisation from RPC instruments, we construct an ionosphere model and compare it to the new cross-calibrated electron density dataset

    Results. We find that the photoionisation and elevated ion flow speeds as measured by LAP produce self-consistent densities in a simple cometary ionosphere model based on the cross-calibrated density dataset. The ion velocities are also consistent with the radial ICA ion bulk flows, and are a factor of five times larger than the neutral speeds. Also, the consistent photoionisation estimate lends further evidence that the solar EUV is attenuated everywhere in the cometary ionosphere at peak activities. We also find that electron-impact ionisation seems to increase with decreasing cometocentric distance. This points towards an external source of hot electrons that are accelerated by a (generally radial) ambipolar electric field, which also have been hypothesised to be the mechanism behind the elevated ion speeds.

    Conclusions. The cometary ionospheric densities as measured by Rosetta is consistent with a model where an ambipolar electric field strongly affects the distribution of the plasma, and collisions play only a minor role. The attenuation of the EUV in the cometary ionosphere reported cannot be local, and is only readily explained by a significant population of nanodust, produced beyond 2000 km in the comet-sun direction via erosion or fragmentation of larger grains.

  • 28.
    Johansson, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Waite, J. H.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Miller, K.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Dreyer, Joshua
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Implications from secondary emission from neutral impact on Cassini plasma and dust measurements2022In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 515, no 2, p. 2340-2350Article in journal (Refereed)
    Abstract [en]

    We investigate the role of secondary electron and ion emission from impact of gas molecules on the Cassini Langmuir probe (RPWS-LP or LP) measurements in the ionosphere of Saturn. We add a model of the emission currents, based on laboratory measurements and data from comet 1P/Halley, to the equations used to derive plasma parameters from LP bias voltage sweeps. Reanalysing several hundred sweeps from the Cassini Grand Finale orbits, we find reasonable explanations for three open conundrums from previous LP studies of the Saturn ionosphere. We find an explanation for the observed positive charging of the Cassini spacecraft, the possibly overestimated ionospheric electron temperatures, and the excess ion current reported. For the sweeps analysed in detail, we do not find (indirect or direct) evidence of dust having a significant charge-carrying role in Saturn's ionosphere. We also produce an estimate of H2O number density from the last six revolutions of Cassini through Saturn's ionosphere in greater detail than reported by the Ion and Neutral Mass Spectrometer. Our analysis reveals an ionosphere that is highly structured in latitude across all six final revolutions, with mixing ratios varying with two orders of magnitude in latitude and one order of magnitude between revolutions and altitude. The result is generally consistent with an empirical photochemistry model balancing the production of H+ ions with the H+ loss through charge transfer with e.g. H2O, CH4, and CO2, for which water vapour appears as the likeliest dominant source of the signal in terms of yield and concentration.

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  • 29.
    Kalha, Curran
    et al.
    UCL, Dept Chem, 20 Gordon St, London WC1H 0AJ, England..
    Fernando, Nathalie K.
    UCL, Dept Chem, 20 Gordon St, London WC1H 0AJ, England..
    Bhatt, Prajna
    UCL, Dept Chem, 20 Gordon St, London WC1H 0AJ, England..
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Medina, León Zendejas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Lindblad, Rebecka
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Siol, Sebastian
    Empa, Swiss Fed Labs Mat Sci & Technol, Lab Joining Technol & Corros, Dubendorf, Switzerland..
    Jeurgens, Lars P. H.
    Empa, Swiss Fed Labs Mat Sci & Technol, Lab Joining Technol & Corros, Dubendorf, Switzerland..
    Cancellieri, Claudia
    Empa, Swiss Fed Labs Mat Sci & Technol, Lab Joining Technol & Corros, Dubendorf, Switzerland..
    Rossnagel, Kai
    Univ Kiel, Inst Expt & Appl Phys, D-24098 Kiel, Germany.;Deutsch Elektronen Synchrotron DESY, Ruprecht Haensel Lab, D-22607 Hamburg, Germany..
    Medjanik, Katerina
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55128 Mainz, Germany..
    Schonhense, Gerd
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55128 Mainz, Germany..
    Simon, Marc
    Sorbonne Univ, CNRS, Lab Chim Phys Matiere & Rayonnement, F-75005 Paris, France..
    Gray, Alexander X.
    Temple Univ, Dept Phys, Philadelphia, PA 19122 USA..
    Nemsak, Slavomir
    Lawrence Berkeley Natl Lab, Adv Light Source, Berkeley, CA 94720 USA..
    Loemker, Patrick
    Deutsch Elektronen Synchrotron DESY, D-22607 Hamburg, Germany..
    Schlueter, Christoph
    Deutsch Elektronen Synchrotron DESY, D-22607 Hamburg, Germany..
    Regoutz, Anna
    UCL, Dept Chem, 20 Gordon St, London WC1H 0AJ, England..
    Hard x-ray photoelectron spectroscopy: a snapshot of the state-of-the-art in 20202021In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 33, no 23, article id 233001Article, review/survey (Refereed)
    Abstract [en]

    Hard x-ray photoelectron spectroscopy (HAXPES) is establishing itself as an essential technique for the characterisation of materials. The number of specialised photoelectron spectroscopy techniques making use of hard x-rays is steadily increasing and ever more complex experimental designs enable truly transformative insights into the chemical, electronic, magnetic, and structural nature of materials. This paper begins with a short historic perspective of HAXPES and spans from developments in the early days of photoelectron spectroscopy to provide an understanding of the origin and initial development of the technique to state-of-the-art instrumentation and experimental capabilities. The main motivation for and focus of this paper is to provide a picture of the technique in 2020, including a detailed overview of available experimental systems worldwide and insights into a range of specific measurement modi and approaches. We also aim to provide a glimpse into the future of the technique including possible developments and opportunities.

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  • 30.
    Myllys, M.
    et al.
    CNRS, LPC2E, Orleans, France.
    Henri, P.
    CNRS, LPC2E, Orleans, France.
    Galand, M.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
    Heritier, K. L.
    Imperial Coll London, Dept Phys, Prince Consort Rd, London SW7 2AZ, England.
    Gilet, N.
    CNRS, LPC2E, Orleans, France.
    Goldstein, R.
    Southwest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Deca, J.
    Univ Colorado, LASP, Boulder, CO 80309 USA;NASA, Inst Modeling Plasma Atmospheres & Cosm Dust, SSERVI, Moffett Field, CA USA.
    Plasma properties of suprathermal electrons near comet 67P/Churyumov-Gerasimenko with Rosetta2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A42Article in journal (Refereed)
    Abstract [en]

    Context: The Rosetta spacecraft escorted comet 67P/Churyumov-Gerasimenko from 2014 to September 2016. The mission provided in situ observations of the cometary plasma during different phases of the cometary activity, which enabled us to better understand its evolution as a function of heliocentric distance.

    Aims: In this study, different electron populations, called warm and hot, observed by the Ion and Electron Sensor (IES) of the Rosetta Plasma Consortium (RPC) are investigated near the comet during the escorting phase of the Rosetta mission.

    Methods: The estimates for the suprathermal electron densities and temperatures were extracted using IES electron data by fitting a double-kappa function to the measured velocity distributions. The fitting results were validated using observations from other RPC instruments. We give upgraded estimates for the warm and hot population densities compared to values previously shown in literature.

    Results: The fitted density and temperature estimates for both electron populations seen by IES are expressed as a function of heliocentric distance to study their evolution with the cometary activity. In addition, we studied the dependence between the electron properties and cometocentric distance.

    Conclusions: We observed that when the neutral outgassing rate of the nucleus is high (i.e., near perihelion) the suprathermal electrons are well characterized by a double-kappa distribution. In addition, warm and hot populations show a significant dependence with the heliocentric distance. The populations become clearly denser near perihelion while their temperatures are observed to remain almost constant. Moreover, the warm electron population density is shown to be strongly dependent on the radial distance from the comet. Finally, based on our results we reject the hypothesis that hot electron population seen by IES consists of solely suprathermal (halo) solar wind electrons, while we suggest that the hot electron population mainly consists of solar wind thermal electrons that have undergone acceleration near the comet.

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  • 31.
    Nilsson, Hans
    et al.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.
    Williamson, Hayley
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.
    Bergman, Sofia
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.
    Wieser, Gabriella Stenberg
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.
    Wieser, Martin
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.
    Behar, Etienne
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden.;Unversite Paris Saclay, Sorbonne Univ, Observ Paris Meudon, Lab Phys Plasmas,CNRS,Ecole Potytech, F-91128 Palaiseau, France.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Richter, Ingo
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany.
    Goetz, Charlotte
    European Space Agcy, ESTEC, Keplerlaan 1, NL-2201 AZ Noordwijk, Netherlands.
    Average cometary ion flow pattern in the vicinity of comet 67P from moment data2020In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 498, no 4, p. 5263-5272Article in journal (Refereed)
    Abstract [en]

    Average flow patterns of ions around comet 67P detected by the RPC-ICA instrument onboard Rosetta are presented both as a time series and as a spatial distribution of the average flow in the plane perpendicular to the comet - Sun direction (Y-Z plane in the coordinate systems used). Cometary ions in the energy range up to 60 eV flow radially away from the nucleus in the Y-Z plane, irrespective of the direction of the magnetic field, throughout the mission. These ions may however be strongly affected by the spacecraft potential, the uncertainty due to this is briefly discussed. Inside the solar wind ion cavity and in the periods just before and after, the cometary pick up ions moving antisunward are deflected against the inferred solar wind electric field direction. This is opposite to what is observed for lower levels of mass-loading. These pick up ions are behaving in a similar way to the solar wind ions and are deflected due to mass-loading. A spatial asymmetry can be seen in the observations of deflected pick up ions, with motion against the electric field primarily within a radius of 200 km of the nucleus and also in the negative electric field hemisphere. Cometary ions observed by RPC-ICA typically move in the antisunward direction throughout the mission. These are average patterns, full-resolution data show very much variability.

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  • 32.
    Odelstad, Elias
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Tzou, C. -Y
    Univ Bern, Phys Inst, Bern, Switzerland.
    Carr, C.
    Univ London Imperial Coll Sci Technol & Med, Space & Atmospher Phys Grp, London, England..
    Cupido, E.
    Univ London Imperial Coll Sci Technol & Med, Space & Atmospher Phys Grp, London, England..
    Evolution of the plasma environment of comet 67P from spacecraft potential measurements by the Rosetta Langmuir probe instrument2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 23Article in journal (Refereed)
    Abstract [en]

    We study the evolution of the plasma environment of comet 67P using measurements of the spacecraft potential from early September 2014 (heliocentric distance 3.5 AU) to late March 2015 (2.1 AU) obtained by the Langmuir probe instrument. The low collision rate keeps the electron temperature high (similar to 5 eV), resulting in a negative spacecraft potential whose magnitude depends on the electron density. This potential is more negative in the northern (summer) hemisphere, particularly over sunlit parts of the neck region on the nucleus, consistent with neutral gas measurements by the Cometary Pressure Sensor of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis. Assuming constant electron temperature, the spacecraft potential traces the electron density. This increases as the comet approaches the Sun, most clearly in the southern hemisphere by a factor possibly as high as 20-44 between September 2014 and January 2015. The northern hemisphere plasma density increase stays around or below a factor of 8-12, consistent with seasonal insolation change.

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  • 33.
    Odelstad, Elias
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, Pierre
    Gilet, Nicolas
    Héritier, Kevin
    Vallières, Xavier
    Rubin, Martin
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 7, p. 5870-5893Article in journal (Refereed)
    Abstract [en]

    Abstract A major point of interest in cometary plasma physics has been the diamagnetic cavity, an unmagnetized region in the innermost part of the coma. Here we combine Langmuir and Mutual Impedance Probe measurements to investigate ion velocities and electron temperatures in the diamagnetic cavity of comet 67P, probed by the Rosetta spacecraft. We find ion velocities generally in the range 2?4 km/s, significantly above the expected neutral velocity 1 km/s, showing that the ions are (partially) decoupled from the neutrals, indicating that ion-neutral drag was not responsible for balancing the outside magnetic pressure. Observations of clear wake effects on one of the Langmuir probes showed that the ion flow was close to radial and supersonic, at least with respect to the perpendicular temperature, inside the cavity and possibly in the surrounding region as well. We observed spacecraft potentials  V throughout the cavity, showing that a population of warm (?5 eV) electrons was present throughout the parts of the cavity reached by Rosetta. Also, a population of cold ( ) electrons was consistently observed throughout the cavity, but less consistently in the surrounding region, suggesting that while Rosetta never entered a region of collisionally coupled electrons, such a region was possibly not far away during the cavity crossings.

  • 34.
    Odelstad, Elias
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Stenberg-Wieser, Gabriella
    Institutet för rymdfysik, Kirunaavdelningen, Swedish Institute of Space Physics, Kiruna Division.
    Wieser, Martin
    Institutet för rymdfysik, Kirunaavdelningen, Swedish Institute of Space Physics, Kiruna Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, Hans
    Institutet för rymdfysik, Kirunaavdelningen, Swedish Institute of Space Physics, Kiruna Division.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Measurements of the electrostatic potential of Rosetta at comet 67P2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, no Suppl. 2, p. S568-S581Article in journal (Refereed)
    Abstract [en]

    We present and compare measurements of the spacecraft potential (Vs/c) of the Rosetta spacecraft throughout its stay in the inner coma of comet 67P/Churyumov-Gerasimenko, by the Rosetta Plasma Consortium-LAngmuir Probe (RPC-LAP) and Ion Composition Analyzer (RPC-ICA) instruments. Vs/c has mainly been negative, driven by the high temperature (~5-10 eV) of the coma photoelectrons. The magnitude of the negative Vs/c traces heliocentric, cometocentric, seasonal and diurnal variations in cometary outgassing, consistent with production at or inside the cometocentric distance of the spacecraft being the dominant source of the observed plasma. LAP only picks up a portion of the full Vs/c since the two probes, mounted on booms of 2.2 and 1.6 m length, respectively, are generally inside the potential field of the spacecraft. Comparing with the minimum energy of positive ions collected by ICA, we find numerous cases with strong correlation between the two instruments, from which the fraction of Vs/c picked up by LAP is found to vary between about 0.7 and 1. We also find an ICA energy offset of 13.7 eV (95 per cent CI: [12.5, 15.0]). Many cases of poor correlation between the instruments are also observed, predominantly when local ion production is weak and accelerated ions dominate the flux, or during quiet periods with low dynamic range in Vs/c and consequently low signal-to-noise ratios.

  • 35.
    Odelstad, Elias
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Stenberg-Wieser, Gabriella
    Institutet för rymdfysik, Kirunaavdelningen, Swedish Institute of Space Physics, Kiruna Division.
    Wieser, Martin
    Institutet för rymdfysik, Kirunaavdelningen, Swedish Institute of Space Physics, Kiruna Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, Hans
    Institutet för rymdfysik, Kirunaavdelningen, Swedish Institute of Space Physics, Kiruna Division.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Measurements of the electrostatic potential of Rosetta at comet 67P2016In: Proceedings of the 14th Spacecraft Charging Technology Conference, Noordwijk, The Netherlands: ESA Publications Division, European Space Agency , 2016, p. Abstract 123-Conference paper (Other academic)
    Abstract [en]

    We present and compare measurements of the spacecraft potential (Vs/c) of ESA:s Rosetta spacecraft, currently in orbit around comet 67P/Churyumov-Gerasimenko, by the Langmuir probe (RPC-LAP) and Ion Composition Analyzer (RPC-ICA) instruments. Vs/c has mainly been negative, driven so by the high (∼5 eV) temperature of the coma photoelectrons. LAP only picks up a portion of the full Vs/c since the two probes, mounted on booms of 2.2 and 1.6 m length, respectively, are generally in- side the potential field of the spacecraft. Comparison to the minimum energy of collected positive ions by ICA shows that this portion varies between 0.7 and 0.9Vs/c, with generally good correspondence between the two in- struments except when local ion production is weak and accelerated ions dominate the flux. 

  • 36.
    Sassa, Yasmine
    et al.
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden.;Uppsala Univ, Dept Phys & Astron, SE-75236 Uppsala, Sweden..
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Yazdi, Milad G.
    KTH Royal Inst Technol, Mat & Nanophys, Electrum 229, SE-16440 Kista, Sweden..
    Simonov, Konstantin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Weissenrieder, Jonas
    KTH Royal Inst Technol, Mat & Nanophys, Electrum 229, SE-16440 Kista, Sweden..
    Muntwiler, Matthias
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Iyikanat, Fadil
    Izmir Inst Technol, Dept Phys, TR-35430 Izmir, Turkey..
    Sahin, Hasan
    Izmir Inst Technol, Dept Photon, TR-35430 Izmir, Turkey..
    Angot, Thierry
    Aix Marseille Univ, CNRS, PIIM, Marseille, France..
    Salomon, Eric
    Aix Marseille Univ, CNRS, PIIM, Marseille, France..
    Le Lay, Guy
    Aix Marseille Univ, CNRS, PIIM, Marseille, France..
    Kagome-like silicene: A novel exotic form of two-dimensional epitaxial silicon2020In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 530, article id 147195Article in journal (Refereed)
    Abstract [en]

    Since the discovery of graphene, intensive efforts have been made in search of novel two-dimensional (2D) materials. Decreasing the materials dimensionality to their ultimate thinness is a promising route to unveil new physical phenomena, and potentially improve the performance of devices. Among recent 2D materials, analogs of graphene, the group IV elements have attracted much attention for their unexpected and tunable physical properties. Depending on the growth conditions and substrates, several structures of silicene, germanene, and stanene can be formed. Here, we report the synthesis of a Kagome-like lattice of silicene on aluminum (1 1 1) substrates. We provide evidence of such an exotic 2D Si allotrope through scanning tunneling microscopy (STM) observations, high-resolution core-level (CL) and angle-resolved photoelectron spectroscopy (ARPES) measurements, along with Density Functional Theory calculations.

  • 37.
    Stephenson, P.
    et al.
    Imperial Coll London, Dept Phys, London SW7 2AZ, England..
    Galand, M.
    Imperial Coll London, Dept Phys, London SW7 2AZ, England..
    Feldman, P. D.
    Johns Hopkins Univ, Phys & Astron, 3400 N Charles St, Baltimore, MD 21218 USA..
    Beth, A.
    Umeå Univ, Dept Phys, S-90187 Umeå, Sweden..
    Rubin, M.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Bockelee-Morvan, D.
    Univ Paris 05, Univ PSL, Sorbonne Univ, Observ Paris,LESIA,CNRS, 5 Pl Jules Janssen, F-92195 Meudon, France..
    Biver, N.
    Univ Paris 05, Univ PSL, Sorbonne Univ, Observ Paris,LESIA,CNRS, 5 Pl Jules Janssen, F-92195 Meudon, France..
    Cheng, Y. -C
    Parker, J.
    Southwest Res Inst, Dept Space Studies, Suite 300,1050 Walnut St, Boulder, CO 80302 USA..
    Burch, J.
    SouthWest Res Inst, PO Drawer 28510, San Antonio, TX 78228 USA..
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Multi-instrument analysis of far-ultraviolet aurora in the southern hemisphere of comet 67P/Churyumov-Gerasimenko2021In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 647, article id A119Article in journal (Refereed)
    Abstract [en]

    Aims: We aim to determine whether dissociative excitation of cometary neutrals by electron impact is the major source of far-ultraviolet (FUV) emissions at comet 67P/Churyumov-Gerasimenko in the southern hemisphere at large heliocentric distances, both during quiet conditions and impacts of corotating interaction regions observed in the summer of 2016.

    Methods: We combined multiple datasets from the Rosetta mission through a multi-instrument analysis to complete the first forward modelling of FUV emissions in the southern hemisphere of comet 67P and compared modelled brightnesses to observations with the Alice FUV imaging spectrograph. We modelled the brightness of OI1356, OI1304, Lyman-beta, CI1657, and CII1335 emissions, which are associated with the dissociation products of the four major neutral species in the coma: CO2, H2O, CO, and O-2. The suprathermal electron population was probed by the Ion and Electron Sensor of the Rosetta Plasma Consortium and the neutral column density was constrained by several instruments: the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), the Microwave Instrument for the Rosetta Orbiter and the Visual InfraRed Thermal Imaging Spectrometer.

    Results: The modelled and observed brightnesses of the FUV emission lines agree closely when viewing nadir and dissociative excitation by electron impact is shown to be the dominant source of emissions away from perihelion. The CII1335 emissions are shown to be consistent with the volume mixing ratio of CO derived from ROSINA. When viewing the limb during the impacts of corotating interaction regions, the model reproduces brightnesses of OI1356 and CI1657 well, but resonance scattering in the extended coma may contribute significantly to the observed Lyman-beta and OI1304 emissions. The correlation between variations in the suprathermal electron flux and the observed FUV line brightnesses when viewing the comet's limb suggests electrons are accelerated on large scales and that they originate in the solar wind. This means that the FUV emissions are auroral in nature.

  • 38.
    Vigren, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Altwegg, K.
    Univ Bern, Inst Phys, Bern, Switzerland..
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders. I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Galand, M.
    Imperial Coll London, Dept Phys, London, England..
    Henri, P.
    Lab Phys & Chim Environm & Espace, Orleans, France..
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics. Lab Phys & Chim Environm & Espace, Orleans, France..
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Tzou, C. -Y
    Vallieres, X.
    Lab Phys & Chim Environm & Espace, Orleans, France..
    Model-Observation Comparisons Of Electron Number Densities In The Coma Of 67P/Churyumov-Gerasimenko During 2015 January2016In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 152, no 3, article id 59Article in journal (Refereed)
    Abstract [en]

    During 2015 January 9-11, at a heliocentric distance of similar to 2.58-2.57 au, the ESA Rosetta spacecraft resided at a cometocentric distance of similar to 28 km from the nucleus of comet 67P/Churyumov-Gerasimenko, sweeping the terminator at northern latitudes of 43 degrees N-58 degrees N. Measurements by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/Comet Pressure Sensor (ROSINA/COPS) provided neutral number densities. We have computed modeled electron number densities using the neutral number densities as input into a Field Free Chemistry Free model, assuming H2O dominance and ion-electron pair formation by photoionization only. A good agreement (typically within 25%) is found between the modeled electron number densities and those observed from measurements by the Mutual Impedance Probe (RPC/MIP) and the Langmuir Probe (RPC/LAP), both being subsystems of the Rosetta Plasma Consortium. This indicates that ions along the nucleus-spacecraft line were strongly coupled to the neutrals, moving radially outward with about the same speed. Such a statement, we propose, can be further tested by observations of H3O+/H2O+ number density ratios and associated comparisons with model results.

  • 39.
    Vigren, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Engelhardt, Ilka. A. D.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Galand, M.
    Imperial Coll London, Dept Phys, London SW7 2AZ, England.
    Goetz, C.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, D-38106 Braunschweig, Germany.
    Henri, P.
    Lab Phys & Chim Environm & Espace, F-45071 Orleans 2, France.
    Heritier, K.
    Imperial Coll London, Dept Phys, London SW7 2AZ, England.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Nilsson, H.
    Swedish Inst Space Phys Kiruna, SE-98128 Kiruna, Sweden.
    Odelstad, Elias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Rubin, M.
    Univ Bern, Inst Phys, CH-3012 Bern, Switzerland.
    Stenberg-Wieser, G.
    Swedish Inst Space Phys Kiruna, SE-98128 Kiruna, Sweden.
    Tzou, C. -Y
    Vallieres, X.
    Lab Phys & Chim Environm & Espace, F-45071 Orleans 2, France.
    Effective ion speeds at similar to 200-250 km from comet 67P/Churyumov-Gerasimenko near perihelion2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S142-S148Article in journal (Refereed)
    Abstract [en]

    In 2015 August, comet 67P/Churyumov-Gerasimenko, the target comet of the ESA Rosetta mission, reached its perihelion at similar to 1.24 au. Here, we estimate for a three-day period near perihelion, effective ion speeds at distances similar to 200-250 km from the nucleus. We utilize two different methods combining measurements from the Rosetta Plasma Consortium (RPC)/Mutual Impedance Probe with measurements either from the RPC/Langmuir Probe or from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Comet Pressure Sensor (COPS) (the latter method can only be applied to estimate the effective ion drift speed). The obtained ion speeds, typically in the range 2-8 km s(-1), are markedly higher than the expected neutral outflow velocity of similar to 1 km s(-1). This indicates that the ions were de-coupled from the neutrals before reaching the spacecraft location and that they had undergone acceleration along electric fields, not necessarily limited to acceleration along ambipolar electric fields in the radial direction. For the limited time period studied, we see indications that at increasing distances from the nucleus, the fraction of the ions' kinetic energy associated with radial drift motion is decreasing.

  • 40.
    Vigren, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Dreyer, Joshua
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Empirical Photochemical Modeling of Saturn's Ionization Balance Including Grain Charging2022In: The Planetary Science Journal, E-ISSN 2632-3338, Vol. 3, no 2, article id 49Article in journal (Refereed)
    Abstract [en]

    We present a semianalytical photochemical model of Saturn's near-equatorial ionosphere and adapt it to two regions (similar to 2200 and similar to 1700 km above the 1 bar level) probed during the inbound portion of Cassini's orbit 292 (2017 September 9). The model uses as input the measured concentrations of molecular hydrogen, hydrogen ion species, and free electrons, as well as the measured electron temperature. The output includes upper limits, or constraints, on the mixing ratios of two families of molecules, on ion concentrations, and on the attachment rates of electrons and ions onto dust grains. The model suggests mixing ratios of the two molecular families that, particularly near similar to 1700 km, differ notably from what independent measurements by the Ion Neutral Mass Spectrometer suggest. Possibly connected to this, the model suggests an electron-depleted plasma with a level of electron depletion of around 50%. This is in qualitative agreement with interpretations of Radio Plasma Wave Science/Langmuir Probe measurements, but an additional conundrum arises in the fact that a coherent photochemical equilibrium scenario then relies on a dust component with typical grain radii smaller than 3 angstrom.

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  • 41.
    Vigren, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Galand, M.
    Imperial Coll London, Dept Phys, London, England.
    Henri, P.
    Lab Phys & Chim Environm & Espace, Orleans, France.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Odelstad, E.
    Royal Inst Technol, Dept Space & Plasma Phys, Stockholm, Sweden.
    Rubin, M.
    Univ Bern, Phys Inst, Bern, Switzerland.
    Vallieres, X.
    Lab Phys & Chim Environm & Espace, Orleans, France.
    The Evolution of the Electron Number Density in the Coma of Comet 67P at the Location of Rosetta from 2015 November through 2016 March2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 881, no 1, article id 6Article in journal (Refereed)
    Abstract [en]

    A comet ionospheric model assuming the plasma moves radially outward with the same bulk speed as the neutral gas and not being subject to severe reduction through dissociative recombination has previously been tested in a series of case studies associated with the Rosetta mission at comet 67P/Churyumov-Gerasimenko. It has been found that at low activity and within several tens of kilometers from the nucleus such models (which originally were developed for such conditions) generally work well in reproducing observed electron number densities, in particular when plasma production through both photoionization and electron-impact ionization is taken into account. Near perihelion, case studies have, on the contrary, shown that applying similar assumptions overestimates the observed electron number densities at the location of Rosetta. Here we compare Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/Comet Pressure sensor-driven model results with Rosetta Plasma Consortium/Mutual Impedance Probe-derived electron number densities for an extended time period (2015 November through 2016 March) during the postperihelion phase with southern summer/spring. We observe a gradual transition from a state when the model grossly overestimates (by more than a factor of 10) the observations to being in reasonable agreement during 2016 March.

  • 42.
    Vigren, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Johansson, Fredrik L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Marschall, R.
    Southwest Res Inst, Dept Space Studies, Boulder, CO USA..
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Rubin, M.
    Univ Bern, Phys Inst, CH-3012 Bern, Switzerland..
    A Case for a Small to Negligible Influence of Dust Charging on the Ionization Balance in the Coma of Comet 67P2021In: The Planetary Science Journal, E-ISSN 2632-3338, Vol. 2, no 4, article id 156Article in journal (Refereed)
    Abstract [en]

    A recent work aided by Rosetta in situ measurements set constraints on the dust-to-gas mass emission ratio and the size distribution of dust escaping the nucleus of comet 67P/Churyumov-Gerasimenko near perihelion. Here we use this information along with other observables/parameters as input into an analytical model aimed at estimating the number density of electrons attached to dust particles near the position of Rosetta. These theoretical estimates are compared to in situ measurements of the degree of ionization. The comparison proposes that Rosetta, while near perihelion, was typically not in electron-depleted regions of the inner coma of 67P. Our work suggests a typical level of electron depletion probably below 10% and possibly below 1%. In line with previous studies, we find, again with certain assumptions and other observables/parameters as input, that the observed negative spacecraft charging to a few tens of volts does not significantly impact the detection of charged dust grains, with a possible exception for grains with radii less than similar to 10 nm.

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