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  • 1.
    Andrews, David J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cowley, S. W. H.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England.
    Provan, G.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England.
    Hunt, G. J.
    Imperial Coll London, Blackett Lab, London, England.
    Hadid, Lina Z
    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.
    The Structure of Planetary Period Oscillations in Saturn's Equatorial Magnetosphere: Results From the Cassini Mission2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 11, p. 8361-8395Article in journal (Refereed)
    Abstract [en]

    Saturn's magnetospheric magnetic field, planetary radio emissions, plasma populations, and magnetospheric structure are all known to be modulated at periods close to the assumed rotation period of the planetary interior. These oscillations are readily apparent despite the high degree of axisymmetry in the internally produced magnetic field of the planet and have different rotation periods in the northern and southern hemispheres. In this paper we study the spatial structure of (near-)planetary period magnetic field oscillations in Saturn's equatorial magnetosphere. Extending previous analyses of these phenomena, we include all suitable data from the entire Cassini mission during its orbital tour of the planet so as to be able to quantify both the amplitude and phase of these field oscillations throughout Saturn's equatorial plane, to distances of 30 planetary radii. We study the structure of these field oscillations in view of both independently rotating northern and southern systems, finding spatial variations in both magnetic fields and inferred currents flowing north-south that are common to both systems. With the greatly expanded coverage of the equatorial plane achieved during the latter years of the mission, we are able to present a complete survey of dawn-dusk and day-night asymmetries in the structure of the oscillating fields and currents. We show that the general structure of the rotating currents is simpler than previously reported and that the relatively enhanced nightside equatorial fields and currents are due in part to related periodic vertical motion of Saturn's magnetotail current sheet.

  • 2.
    Boldu O Farrill Treviño, Joan Jordi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Graham, Daniel B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    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.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Dimmock, Andrew P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Soucek, J.
    Pisa, D.
    Maksimovic, M.
    Ion-acoustic waves associated with interplanetary shocks2023In: Article in journal (Other academic)
  • 3.
    Chatain, A.
    et al.
    Univ Paris Saclay, UVSQ, CNRS, LATMOS, Guyancourt, France.;Sorbonne Univ, CNRS, Inst Polytech Paris, LPP,Ecole Polytech, Palaiseau, France..
    Wahlund, Jan-Erik
    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. Imperial Coll London, South Kensington, England..
    Hadid, Lina Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Sorbonne Univ, CNRS, Inst Polytech Paris, LPP,Ecole Polytech, Palaiseau, France..
    Morooka, Michiko
    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.
    Guaitella, O.
    Sorbonne Univ, CNRS, Inst Polytech Paris, LPP,Ecole Polytech, Palaiseau, France..
    Carrasco, N.
    Univ Paris Saclay, UVSQ, CNRS, LATMOS, Guyancourt, France..
    Re-Analysis of the Cassini RPWS/LP Data in Titan's Ionosphere: 1. Detection of Several Electron Populations2021In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 126, no 8, article id e2020JA028412Article in journal (Refereed)
    Abstract [en]

    Current models of Titan's ionosphere have difficulties in explaining the observed electron density and/or temperature. In order to get new insights, we re-analyzed the data taken in the ionosphere of Titan by the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave Science (RPWS) instrument. This is the first of two papers that present the new analysis method (current paper) and statistics on the whole data set. We suggest that between two and four electron populations are necessary to fit the data. Each population is defined by a potential, an electron density and an electron temperature and is easily visualized by a distinct peak in the second derivative of the electron current, which is physically related to the electron energy distribution function (Druyvesteyn method). The detected populations vary with solar illumination and altitude. We suggest that the four electron populations are due to photo-ionization, magnetospheric particles, dusty plasma and electron emission from the probe boom, respectively.

  • 4.
    Chatain, A.
    et al.
    Univ Paris Saclay, UVSQ, CNRS, LATMOS, Guyancourt, France.;Sorbonne Univ, LPP, CNRS, Ecole Polytech,Inst Polytech Paris, Palaiseau, France..
    Wahlund, Jan-Erik
    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. Imperial Coll London, London, England..
    Hadid, Lina Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Sorbonne Univ, LPP, CNRS, Ecole Polytech,Inst Polytech Paris, Palaiseau, France..
    Morooka, Michiko
    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.
    Guaitella, O.
    Sorbonne Univ, LPP, CNRS, Ecole Polytech,Inst Polytech Paris, Palaiseau, France..
    Carrasco, N.
    Univ Paris Saclay, UVSQ, CNRS, LATMOS, Guyancourt, France..
    Re-Analysis of the Cassini RPWS/LP Data in Titan's Ionosphere: 2. Statistics on 57 Flybys2021In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 126, no 8, article id e2020JA028413Article in journal (Refereed)
    Abstract [en]

    The ionosphere of Titan hosts a complex ion chemistry leading to the formation of organic dust below 1,200 km. Current models cannot fully explain the observed electron temperature in this dusty environment. To achieve new insight, we have re-analyzed the data taken in the ionosphere of Titan by the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave Science package. A first paper (Chatain et al., 2021) introduces the new analysis method and discusses the identification of four electron populations produced by different ionization mechanisms. In this second paper, we present a statistical study of the whole LP dataset below 1,200 km which gives clues on the origin of the four populations. One small population is attributed to photo- or secondary electrons emitted from the surface of the probe boom. A second population is systematically observed, at a constant density (similar to 500 cm(-3)), and is attributed to background thermalized electrons from the ionization process of precipitating particles from the surrounding magnetosphere. The two last populations increase in density with pressure, solar illumination and Extreme ultraviolet flux. The third population is observed with varying densities at all altitudes and solar zenith angles (SZA) except on the far nightside (SZA > similar to 140 degrees), with a maximum density of 2,700 cm(-3). It is therefore certainly related to the photo-ionization of the atmospheric molecules. Finally, a fourth population detected only on the dayside and below 1,200 km reaching up to 2000 cm(-3) could be photo- or thermo-emitted from dust grains.

  • 5.
    Cravens, T. E.
    et al.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Renzaglia, A.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Moore, L.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA.
    Waite, J. H., Jr.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Perryman, R.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Perry, M.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Hadid, Lina Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Plasma Transport in Saturn's Low-Latitude Ionosphere: Cassini Data2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 6, p. 4881-4888Article in journal (Refereed)
    Abstract [en]

    In 2017 the Cassini Orbiter made the first in situ measurements of the upper atmosphere and ionosphere of Saturn. The Ion and Neutral Mass Spectrometer in its ion mode measured densities of light ion species (H+, H-2(+), H-3(+), and He+), and the Radio and Plasma Wave Science instrument measured electron densities. During proximal orbit 287 (denoted P287), Cassini reached down to an altitude of about 3,000 km above the 1 bar atmospheric pressure level. The topside ionosphere plasma densities measured for P287 were consistent with ionospheric measurements during other proximal orbits. Spacecraft potentials were measured by the Radio and Plasma Wave Science Langmuir probe and are typically about negative 0.3 V. Also, for this one orbit, Ion and Neutral Mass Spectrometer was operated in an instrument mode allowing the energies of incident H+ ions to be measured. H+ is the major ion species in the topside ionosphere. Ion flow speeds relative to Saturn's atmosphere were determined. In the southern hemisphere, including near closest approach, the measured ion speeds were close to zero relative to Saturn's corotating atmosphere, but for northern latitudes, southward ion flow of about 3 km/s was observed. One possible interpretation is that the ring shadowing of the southern hemisphere sets up an interhemispheric plasma pressure gradient driving this flow.

  • 6.
    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)
  • 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
    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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  • 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.
    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
  • 9.
    Farrell, W. M.
    et al.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Hadid, Lina Z
    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.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    MacDowall, R. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Sulaiman, A. H.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Saturn's Plasma Density Depletions Along Magnetic Field Lines Connected to the Main Rings2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 16, p. 8104-8110Article in journal (Refereed)
    Abstract [en]

    We report on a set of clear and abrupt decreases in the high-frequency boundary of whistler mode emissions detected by Cassini at high latitudes (about +/- 40 degrees) during the low-altitude proximal flybys of Saturn. These abrupt decreases or dropouts have start and stop locations that correspond to L shells at the edges of the A and B rings. Langmuir probe measurements can confirm, in some cases, that the abrupt decrease in the high-frequency whistler mode boundary is associated with a corresponding abrupt electron density dropout over evacuated field lines connected to the A and B rings. Wideband data also reveal electron plasma oscillations and whistler mode cutoffs consistent with a low-density plasma in the region. The observation of the electron density dropout along ring-connecting field lines suggests that strong ambipolar forces are operating, drawing cold ionospheric ions outward to fill the flux tubes. There is an analog with the refilling of flux tubes in the terrestrial plasmasphere. We suggest that the ring-connected electron density dropouts observed between 1.1 and 1.3 R-s are connected to the low-density ring plasma cavity observed overtop the A and B rings during the 2004 Saturn orbital insertion pass.

    Plain Language Summary We present Cassini observations during the close passes by the planet Saturn indicating that plasma on magnetic field lines that pass through the A and B rings is of anomalously low density. These observations are consistent with the Saturn orbit insertion observations of a plasma cavity located at equatorial regions overtop the dense B ring. Using a terrestrial analogy, we suggest that the low-density conditions overtop the rings create an electrical force, called an ambipolar electric field that draws plasma out of the ionosphere in an attempt to replenish the plasma void found at equatorial regions.

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  • 10. Farrell, W. M.
    et al.
    Wahlund, Jan-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, Department of Physics and Astronomy.
    Gurnett, D. A.
    Kurth, W. S.
    MacDowall, R. J.
    An estimate of the dust pickup current at Enceladus2014In: Icarus, ISSN 0019-1035, E-ISSN 1090-2643, Vol. 239, p. 217-221Article in journal (Refereed)
    Abstract [en]

    We demonstrate that the acceleration of submicron dust originating at Enceladus by a reduced co-rotating E-field is capable of creating a dust pickup current perpendicular to the magnetic field with values ranging from 3 to 15 kA (depending upon the effective grain charge). Such a current represents a new contribution to the total pickup current in the region. As such, we suggest that dust pickup currents, along with ion and electron pickup currents, are all active within the plume.

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  • 11.
    Farrell, W. M.
    et al.
    NASA Goddard Space Flight Ctr, Solar Syst Explorat Div, Greenbelt, MD 20771 USA..
    Wahlund, Jan-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, Department of Physics and Astronomy.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    MacDowall, R. J.
    NASA Goddard Space Flight Ctr, Solar Syst Explorat Div, Greenbelt, MD 20771 USA..
    Ion trapping by dust grains: Simulation applications to the Enceladus plume2017In: Journal of Geophysical Research - Planets, ISSN 2169-9097, E-ISSN 2169-9100, Vol. 122, no 4, p. 729-743Article in journal (Refereed)
    Abstract [en]

    Using a particle-in-cell electrostatic simulation, we examine the conditions that allow low-energy ions, like those produced in the Enceladus plume, to be attracted and trapped within the sheaths of negatively charged dust grains. The conventional wisdom is that all new ions produced in the Enceladus plume are free to get picked up (i.e., accelerated by the local E field to then undergo vB acceleration). However, we suggest herein that the presence of submicron-charged dust in the plume impedes this pickup process since the local grain electric field greatly exceeds the corotation E fields. The simulations demonstrate that cold ions will tend to accelerate toward the negatively charged grains and become part of the ion plasma sheath. These trapped ions will move with the grains, exiting the plume region at the dust speed. We suggest that Cassini's Langmuir probe is measuring the entire ion population (free and trapped ions), while the Cassini magnetometer detects the magnetic perturbations associated with pickup currents from the smaller population of free ions, with this distinction possibly reconciling the ongoing debate in the literature on the ion density in the plume.

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  • 12.
    Hadid, L. Z.
    et al.
    PSL Res Univ, LPP, CNRS, Observ Paris,Sorbonne Univ,Ecole Polytech,Inst Po, F-91120 Palaiseau, France..
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Chust, T.
    PSL Res Univ, LPP, CNRS, Observ Paris,Sorbonne Univ,Ecole Polytech,Inst Po, F-91120 Palaiseau, France..
    Pisa, D.
    Czech Acad Sci, Dept Space Phys, Inst Atmospher Phys, Prague, Czech Republic..
    Dimmock, Andrew P.
    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.
    Maksimovic, M.
    Univ PSL, Sorbonne Univ, Univ Paris, Observ Paris,LESIA,CNRS, Meudon, France..
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Soucek, J.
    Czech Acad Sci, Dept Space Phys, Inst Atmospher Phys, Prague, Czech Republic..
    Kretzschmar, M.
    Univ Orleans, CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Vecchio, A.
    Univ PSL, Sorbonne Univ, Univ Paris, Observ Paris,LESIA,CNRS, Meudon, France.;Radboud Univ Nijmegen, Radboud Radio Lab, Dept Astrophys, Nijmegen, Netherlands..
    Le Contel, O.
    PSL Res Univ, LPP, CNRS, Observ Paris,Sorbonne Univ,Ecole Polytech,Inst Po, F-91120 Palaiseau, France..
    Retino, A.
    PSL Res Univ, LPP, CNRS, Observ Paris,Sorbonne Univ,Ecole Polytech,Inst Po, F-91120 Palaiseau, France..
    Allen, R. C.
    Johns Hopkins Appl Phys Lab, Laurel, MD 20723 USA..
    Volwerk, M.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Fowler, C. M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Sorriso-Valvo, Luca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. CNR, Ist Sci & Tecnol Plasmi ISTP, Via Amendola 122-D, I-70126 Bari, Italy..
    Karlsson, T.
    KTH Royal Inst Technol, Space & Plasma Phys, S-10405 Stockholm, Sweden..
    Santolik, O.
    Czech Acad Sci, Dept Space Phys, Inst Atmospher Phys, Prague, Czech Republic.;Charles Univ Prague, Fac Math & Phys, Prague, Czech Republic..
    Kolmasova, I
    Czech Acad Sci, Dept Space Phys, Inst Atmospher Phys, Prague, Czech Republic.;Charles Univ Prague, Fac Math & Phys, Prague, Czech Republic..
    Sahraoui, F.
    PSL Res Univ, LPP, CNRS, Observ Paris,Sorbonne Univ,Ecole Polytech,Inst Po, F-91120 Palaiseau, France..
    Stergiopoulou, Katerina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Moussas, X.
    Natl & Kapodistrian Univ Athens, Dept Astrophys Astron & Mech, Fac Phys, Sch Sci, Zografos 15783, Greece..
    Issautier, K.
    Univ PSL, Sorbonne Univ, Univ Paris, Observ Paris,LESIA,CNRS, Meudon, France..
    Dewey, R. M.
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Wolt, M. Klein
    Radboud Univ Nijmegen, Radboud Radio Lab, Dept Astrophys, Nijmegen, Netherlands..
    Malandraki, O. E.
    Natl Observ Athens, IAASARS, Metaxa & Vas Pavlou Str, Athens 15236, Greece..
    Kontar, E. P.
    Univ Glasgow, Sch Phys & Astron, Glasgow G12 8QQ, Lanark, Scotland..
    Howes, G. G.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Bale, S. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Horbury, T. S.
    Imperial Coll, Dept Phys, London SW7 2AZ, England..
    Martinovic, M.
    Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA..
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Sch Elect Engn & Comp, Dept Space & Plasma Phys, Stockholm, Sweden..
    Krasnoselskikh, V
    Univ Orleans, CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Lorfevre, E.
    CNES, 18 Ave Edouard Belin, F-31400 Toulouse, France..
    Plettemeier, D.
    Tech Univ Dresden, Warzburger Str 35, D-01187 Dresden, Germany..
    Steller, M.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Stverak, S.
    Czech Acad Sci, Astron Inst, Prague, Czech Republic.;Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic..
    Travnicek, P.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic..
    O'Brien, H.
    Imperial Coll, Dept Phys, London SW7 2AZ, England..
    Evans, V
    Imperial Coll, Dept Phys, London SW7 2AZ, England..
    Angelini, V
    Imperial Coll, Dept Phys, London SW7 2AZ, England..
    Velli, M. C.
    CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA..
    Zouganelis, I
    European Space Agcy ESA, European Space Astron Ctr ESAC, Camino Bajo Castillo S-N, Madrid 28692, Spain..
    Solar Orbiter's first Venus flyby: Observations from the Radio and Plasma Wave instrument2021In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 656, article id A18Article in journal (Refereed)
    Abstract [en]

    Context. On December 27, 2020, Solar Orbiter completed its first gravity assist manoeuvre of Venus (VGAM1). While this flyby was performed to provide the spacecraft with sufficient velocity to get closer to the Sun and observe its poles from progressively higher inclinations, the Radio and Plasma Wave (RPW) consortium, along with other operational in situ instruments, had the opportunity to perform high cadence measurements and study the plasma properties in the induced magnetosphere of Venus.

    Aims. In this paper, we review the main observations of the RPW instrument during VGAM1. They include the identification of a number of magnetospheric plasma wave modes, measurements of the electron number densities computed using the quasi-thermal noise spectroscopy technique and inferred from the probe-to-spacecraft potential, the observation of dust impact signatures, kinetic solitary structures, and localized structures at the bow shock, in addition to the validation of the wave normal analysis on-board from the Low Frequency Receiver.

    Methods. We used the data products provided by the different subsystems of RPW to study Venus' induced magnetosphere.

    Results. The results include the observations of various electromagnetic and electrostatic wave modes in the induced magnetosphere of Venus: strong emissions of similar to 100 Hz whistler waves are observed in addition to electrostatic ion acoustic waves, solitary structures and Langmuir waves in the magnetosheath of Venus. Moreover, based on the different levels of the wave amplitudes and the large-scale variations of the electron number densities, we could identify different regions and boundary layers at Venus.

    Conclusions. The RPW instrument provided unprecedented AC magnetic and electric field measurements in Venus' induced magnetosphere for continuous frequency ranges and with high time resolution. These data allow for the conclusive identification of various plasma waves at higher frequencies than previously observed and a detailed investigation regarding the structure of the induced magnetosphere of Venus. Furthermore, noting that prior studies were mainly focused on the magnetosheath region and could only reach 10-12 Venus radii (R-V) down the tail, the particular orbit geometry of Solar Orbiter's VGAM1, allowed the first investigation of the nature of the plasma waves continuously from the bow shock to the magnetosheath, extending to similar to 70R(V) in the far distant tail region.

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  • 13.
    Hadid, L. Z.
    et al.
    Univ Paris Saclay, Lab Phys Plasmas LPP, CNRS, Observ Paris,Sorbonne Univ,Inst Polytech Paris,Ec, F-91120 Palaiseau, France..
    Shebanits, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Imperial Coll London, Blackett Lab, London SW7 2AZ, England..
    Wahlund, J-E
    Swedish Inst Space Phys, Box 537, SE-75121 Uppsala, Sweden..
    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.
    Nagy, A. F.
    Univ Michigan, Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Farrell, W. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Holmberg, M. K. G.
    ESTEC ESA, NL-2201 AZ Noordwijk, Netherlands..
    Modolo, R.
    LATMOS Lab Atmospheres Milieux Observat Spatiales, F-78280 Guyancourt, France..
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Tseng, W. L.
    Natl Taiwan Normal Univ, Dept Earth Sci, Taipei 11677, Taiwan..
    Ye, S-Y
    Southern Univ Sci & Technol SUSTech, Dept Earth & Space Sci, Shenzhen 518055, Peoples R China..
    Ambipolar electrostatic field in negatively charged dusty plasma2022In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 88, no 2, article id 555880201Article in journal (Refereed)
    Abstract [en]

    We study the effect of negatively charged dust on the magnetic-field-aligned polarisation electrostatic field (E-parallel to) using Cassini's RPWS/LP in situ measurements during the `ring-grazing' orbits. We derive a general expression for E-parallel to and estimate for the first time in situ parallel to E-parallel to parallel to (approximately 10(-5) V m(-1)) near the Janus and Epimetheus rings. We further demonstrate that the presence of the negatively charged dust close to the ring plane (vertical bar Z vertical bar less than or similar to 0.11 R-s) amplifies parallel to E-parallel to parallel to by at least one order of magnitude and reverses its direction due to the effect of the charged dust gravitational and inertial forces. Such reversal confines the electrons at the magnetic equator within the dusty region, around 0.047 R-s above the ring plane. Furthermore, we discuss the role of the collision terms, in particular the ion-dust drag force, in amplifying E-parallel to. These results imply that the charged dust, as small as nanometres in size, can have a significant influence on the plasma transport, in particular ambipolar diffusion along the magnetic field lines, and so their presence must be taken into account when studying such dynamical processes.

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  • 14.
    Hadid, Lina Z
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko W.
    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.
    Moore, L.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA.
    Cravens, T. E.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Hedman, M. M.
    Univ Idaho, Dept Phys, Moscow, ID USA.
    Edberg, Niklas J. T.
    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.
    Waite, J. H., Jr.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Perryman, R.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Farrell, W. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ring Shadowing Effects on Saturn's Ionosphere: Implications for Ring Opacity and Plasma Transport2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 19, p. 10084-10092Article in journal (Refereed)
    Abstract [en]

    We present new results obtained by the Radio and Plasma Wave Science Langmuir probe on board Cassini during the Grand Finale. The total direct current sampled by the Langmuir probe at negative bias voltage is used to study the effect of the ring shadows on the structure of the Kronian topside ionosphere. The D and C rings and the Cassini Division are confirmed to be optically thin to extreme ultraviolet solar radiation. However, different responses from the opaque A and B rings are observed. The edges of the A ring shadow are shown to match the A ring boundaries, unlike the B ring, which indicates variable responses to the B ring shadow. We show that the variable responses are due to the ionospheric plasma, more precisely to the longer chemical lifetime of H+ compared to H-2(+) and H-3(+), suggesting that the plasma is transported from the sunlit region to the shadowed one in the ionosphere. Plain Language Summary As Saturn's northern hemisphere experienced summer during the Grand Finale, the planet's northern dayside hemisphere and its rings were fully illuminated by the Sun. However, the southern hemisphere was partly obscured because of the shadows cast by the A and B rings. Using the in situ measurements of the Langmuir probe part of the Radio and Plasma Wave Science investigation on board the Cassini spacecraft, we study for the first time the effect of the ring shadows on Saturn's ionosphere. From the ring shadows signatures on the total ion current collected by the Langmuir probe, we show that the A and B rings are optically thicker (to the solar extreme ultraviolet radiation) than the inner C and D rings and the Cassini Division to the solar extreme ultraviolet radiation. Moreover, we reproduce the boundaries of the A ring and the outer edge of the B ring. Furthermore, observed variations with respect to the inner edge of the B ring imply a delayed response of the ionospheric H+ because of its long lifetime and suggest that the ionospheric plasma is transported from an unshadowed region to a shadowed one in the ionosphere.

  • 15.
    Hadid, Lina Z
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko W
    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.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Shebanits, O.
    Imperial Coll London, Blackett Lab, Space & Atmospher Phys, London, England.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    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.
    Nagy, A. F.
    Univ Michigan, Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA.
    Eriksson, Anders I
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Saturn's Ionosphere: Electron Density Altitude Profiles and D-Ring Interaction From The Cassini Grand Finale2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 16, p. 9362-9369Article in journal (Refereed)
    Abstract [en]

    We present the electron density (n(e)) altitude profiles of Saturn's ionosphere at near-equatorial latitudes from all 23 orbits of Cassini's Grand Finale. The data are collected by the Langmuir probe part of the Radio and Plasma Wave Science investigation. A high degree of variability in the electron density profiles is observed. However, organizing them by consecutive altitude ranges revealed clear differences between the southern and northern hemispheres. The n(e) profiles are shown to be more variable and connected to the D-ring below 5,000 km in the southern hemisphere compared to the northern hemisphere. This observed variability is explained to be a consequence of an electrodynamic interaction with the D-ring. Moreover, a density altitude profile is constructed for the northern hemisphere indicating the presence of three different ionospheric layers. Similar properties were observed during Cassini's final plunge, where the main ionospheric peak is crossed at similar to 1,550-km altitude. Plain Language Summary The Cassini Langmuir probe measured directly the uppermost layer of Saturn's atmosphere, the ionosphere, during its Grand Finale. The observations revealed a layered electron density altitude profile with evidence in the southern hemisphere of an electrodynamic type of interaction with the planet innermost D-ring. Moreover, the main peak of the ionosphere is observed for the first time in the final plunge around 1,550 km.

  • 16.
    Holmberg, M. K. G.
    et al.
    European Space Research and Technology Center, European Space Agency, Noordwijk, The Netherlands.
    Cipriani, F.
    European Space Research and Technology Center, European Space Agency, Noordwijk, The Netherlands.
    Nilsson, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hess, S.
    DESP - Space Environment Department, ONERA, Toulouse, France.
    Huybrighs, H. L. F.
    European Space Research and Technology Center, European Space Agency, Noordwijk, The Netherlands.
    Hadid, L. Z.
    European Space Research and Technology Center, European Space Agency, Noordwijk, The Netherlands.
    Déprez, G.
    European Space Research and Technology Center, European Space Agency, Noordwijk, The Netherlands.
    Wilson, R. J.
    Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, CO, USA.
    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.
    Felici, M.
    Center for Space Physics, Boston University, Boston, MA, USA.
    Cassini-Plasma Interaction Simulations Revealing the Cassini Ion Wake Characteristics: Implications for In-Situ Data Analyses and Ion Temperature Estimates2021In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 126, no 8, article id e2020JA029026Article in journal (Refereed)
    Abstract [en]

    We have used Spacecraft Plasma Interaction Software (SPIS) simulations to study the characteristics (i.e., dimensions, ion depletion, and evolution with the changing spacecraft attitude) of the Cassini ion wake. We focus on two regions, the plasma disk at 4.5-€“4.7 RS, where the most prominent wake structure will be formed, and at 7.6 RS, close to the maximum distance at which a wake structure can be detected in the Cassini Langmuir probe (LP) data. This study also reveals how the ion wake and the spacecraft plasma interaction have impacted the Cassini LP measurements in the studied environments, for example, with a strong decrease in the measured ion density but with minor interference from the photoelectrons and secondary electrons originating from the spacecraft. The simulated ion densities and spacecraft potentials are in very good agreement with the LP measurements. This shows that SPIS is an excellent tool to use for analyses of LP data, when spacecraft material properties and environmental parameters are known and used correctly. The simulation results are also used to put constraints on the ion temperature estimates in the inner magnetosphere of Saturn. The best agreement between the simulated and measured ion density is obtained using an ion temperature of 8 eV at ∼4.6 RS. This study also shows that SPIS simulations can be used in order to better constrain plasma parameters in regions where accurate measurements are not available.

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  • 17.
    Holmberg, M. K. G.
    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. Univ Toulouse, CNES, UPS, IRAP,CNRS, Toulouse, France..
    Shebanits, Oleg
    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.
    Wahlund, Jan-Erik
    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.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Swedish Inst Space Phys, Uppsala, Sweden..
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andre, N.
    Univ Toulouse, CNES, UPS, IRAP,CNRS, Toulouse, France..
    Garnier, P.
    Univ Toulouse, CNES, UPS, IRAP,CNRS, Toulouse, France..
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Genot, V.
    Univ Toulouse, CNES, UPS, IRAP,CNRS, Toulouse, France..
    Gilbert, L. K.
    Univ Coll London, Mullard Space Sci Lab, Dorking, Surrey, England..
    Density Structures, Dynamics, and Seasonal and Solar Cycle Modulations of Saturn's Inner Plasma Disk2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 12, p. 12258-12273Article in journal (Refereed)
    Abstract [en]

    We present statistical results from the Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe measurements recorded during the time interval from orbit 3 (1 February 2005) to 237 (29 June 2016). A new and improved data analysis method to obtain ion density from the Cassini LP measurements is used to study the asymmetries and modulations found in the inner plasma disk of Saturn, between 2.5 and 12 Saturn radii (1 RS = 60, 268 km). The structure of Saturn's plasma disk is mapped, and the plasma density peak, n(max), is shown to be located at similar to 4.6 RS and not at the main neutral source region at 3.95 RS. The shift in the location of n(max) is due to that the hot electron impact ionization rate peaks at similar to 4.6 RS. Cassini RPWS plasma disk measurements show a solar cycle modulation. However, estimates of the change in ion density due to varying EUV flux is not large enough to describe the detected dependency, which implies that an additional mechanism, still unknown, is also affecting the plasma density in the studied region. We also present a dayside/nightside ion density asymmetry, with nightside densities up to a factor of 2 larger than on the dayside. The largest density difference is found in the radial region 4 to 5 RS. The dynamic variation in ion density increases toward Saturn, indicating an internal origin of the large density variability in the plasma disk rather than being caused by an external source origin in the outer magnetosphere.

  • 18.
    Holmberg, Mika
    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.
    Wahlund, Jan-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, Department of Physics and Astronomy.
    Dayside/nightside asymmetry of ion densities and velocities in Saturn's inner magnetosphere2014In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 11, p. 3717-3723Article in journal (Refereed)
    Abstract [en]

    We present Radio and Plasma Wave Science Langmuir probe measurements from 129 Cassini orbits, which show a day/night asymmetry in both ion density and ion velocity in the radial region 4–6 RS (1 RS = 60,268 km) from the center of Saturn. The ion densities ni vary from an average of ∼35 cm−3 around noon up to ∼70 cm−3 around midnight. The ion velocities vi,θ vary from ∼28–32 km/s at the lowest dayside values to ∼36–40 km/s at the highest nightside values. The day/night asymmetry is suggested to be due to the radiation pressure force acting on negatively charged nanometer-sized dust of the E ring. This force will introduce an extra grain and ion drift component equivalent to the force of an additional electric field of 0.1–2 mV/m for 10–50 nm sized grains.

  • 19.
    Karlsson, T.
    et al.
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Div Space & Plasma Phys, Stockholm, Sweden..
    Heyner, D.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Volwerk, M.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Plaschke, F.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Goetz, C.
    ESA, ESTEC SCI S, Noordwijk, Netherlands..
    Hadid, L.
    Univ Paris Saclay, Sorbonne Univ, Observ Paris Meudon, CNRS,Ecole Polytech,Lab Phys Plasmas, Palaiseau, France..
    Magnetic Holes in the Solar Wind and Magnetosheath Near Mercury2021In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 126, no 5, article id e2020JA028961Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive statistical study of magnetic holes, defined as localized decreases of the magnetic field strength of at least 50%, in the solar wind near Mercury, using MESSENGER orbital data. We investigate the distributions of several properties of the magnetic holes, such as scale size, depth, and associated magnetic field rotation. We show that the distributions are very similar for linear magnetic holes (with a magnetic field rotation across the magnetic holes of less than 25 degrees) and rotational holes (rotations >25 degrees), except for magnetic holes with very large rotations (greater than or similar to 140 degrees). Solar wind magnetic hole scale sizes follow a log-normal distribution, which we discuss in terms of multiplicative growth. We also investigate the background magnetic field strength of the solar wind surrounding the magnetic holes, and conclude that it is lower than the average solar wind magnetic field strength. This is consistent with finding solar wind magnetic holes in high-beta regions, as expected if magnetic holes have a connection to magnetic mirror mode structures. We also present, for the first time, comprehensive statistics of isolated magnetic holes in a planetary magnetosheath. The properties of the magnetosheath magnetic holes are very similar to the solar wind counterparts, and we argue that the most likely interpretation is that the magnetosheath magnetic holes have a solar wind origin, rather than being generated locally in the magnetosheath.

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  • 20.
    Karlsson, T.
    et al.
    KTH Royal Inst Technol, Space & Plasma Phys, S-10405 Stockholm, Sweden..
    Kasaba, Y.
    Tohoku Univ, Grad Sch Sci, Planetary Plasma & Atmospher Res Ctr, Sendai, Miyagi 9808578, Japan..
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Henri, P.
    CNRS, LPC2E, Orleans, France.;Univ Cote Azur, Observ Cote Azur, CNRS, Lab Lagrange, Nice, France..
    Bylander, L.
    KTH Royal Inst Technol, Space & Plasma Phys, S-10405 Stockholm, Sweden..
    Puccio, Walter
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Jansson, S. -E
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Åhlén, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Kallio, E.
    Finnish Meteorol Inst, Space Res Unit, Helsinki, Finland..
    Kojima, H.
    Kyoto Univ, Res Inst Sustainable Humanosphere, Uji, Kyoto 6110011, Japan..
    Kumamoto, A.
    Tohoku Univ, Grad Sch Sci, Dept Geophys, Sendai, Miyagi 9808578, Japan..
    Lappalainen, K.
    Univ Oulu, Oulu, Finland..
    Lybekk, B.
    Univ Oslo, Dept Phys, Oslo, Norway..
    Ishisaka, K.
    Toyama Prefectural Univ, Dept Elect & Informat, Imizu, Toyama 9390398, Japan..
    Eriksson, Anders
    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.
    The MEFISTO and WPT Electric Field Sensors of the Plasma Wave Investigation on the BepiColombo Mio Spacecraft Measurements of Low and High Frequency Electric Fields at Mercury2020In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 216, no 8, article id 132Article, review/survey (Refereed)
    Abstract [en]

    This paper describes the design of MEFISTO (Mercury Electric Field In-Situ Tool) and WPT (Wire Probe Antenna) electric field sensors for Plasma Wave Investigation (PWI) on the BepiColombo Mio spacecraft (Mercury Magnetospheric Orbiter, MMO). The two sensors will enable the first observations of electric fields, plasma waves and radio waves in and around the Hermean magnetosphere and exosphere. MEFISTO and WPT are dipole antennas with 31.6 m tip-to-tip length. Each antenna element has a spherical probe at each end of the wire (15 m length). They are extended orthogonally in the spin plane of the spacecraft and enable measurements of the electric field in the frequency range of DC to 10 MHz by the connection to two sets of receivers, EWO for a lower frequency range and SORBET for higher frequencies. In the initial operations after the launch (20 Oct. 2018), we succeeded to confirm the health of both antennas and to release the launch lock of the WPT. After Mercury orbit insertion planned at the end of 2025, both sensors will be fully deployed and activate full operations of the PWI electric field measurements.

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  • 21.
    Lamy, L.
    et al.
    Univ Paris Diderot, Univ Paris Sci & Lettres, Lab Etud Spatiales & Instrumentat Astrophys, Observ Paris,Sorbonne Univ,Sorbonne Paris Cite,CN, 5 Pl Jules Janssen, F-92195 Meudon, France.
    Zarka, P.
    Univ Paris Diderot, Univ Paris Sci & Lettres, Lab Etud Spatiales & Instrumentat Astrophys, Observ Paris,Sorbonne Univ,Sorbonne Paris Cite,CN, 5 Pl Jules Janssen, F-92195 Meudon, France.
    Cecconi, B.
    Univ Paris Diderot, Univ Paris Sci & Lettres, Lab Etud Spatiales & Instrumentat Astrophys, Observ Paris,Sorbonne Univ,Sorbonne Paris Cite,CN, 5 Pl Jules Janssen, F-92195 Meudon, France.
    Prange, R.
    Univ Paris Diderot, Univ Paris Sci & Lettres, Lab Etud Spatiales & Instrumentat Astrophys, Observ Paris,Sorbonne Univ,Sorbonne Paris Cite,CN, 5 Pl Jules Janssen, F-92195 Meudon, France.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Hospodarsky, G.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Persoon, A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    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.
    Hunt, G. J.
    Imperial Coll London, Blackett Lab, London SW7 2BW, England.
    The low-frequency source of Saturn's kilometric radiation2018In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 362, no 6410, article id eaat2027Article in journal (Refereed)
    Abstract [en]

    Understanding how auroral radio emissions are produced by magnetized bodies requires in situ measurements within their source region. Saturn's kilometric radiation (SKR) has been widely used as a remote proxy of Saturn's magnetosphere. We present wave and plasma measurements from the Cassini spacecraft during its ring-grazing high-inclination orbits, which passed three times through the high-altitude SKR emission region. Northern dawn-side, narrow-banded radio sources were encountered at frequencies of 10 to 20 kilohertz, within regions of upward currents mapping to the ultraviolet auroral oval. The kilometric waves were produced on the extraordinary mode by the cyclotron maser instability from 6- to 12-kiloelectron volt electron beams and radiated quasi-perpendicularly to the auroral magnetic field lines. The SKR low-frequency sources appear to be strongly controlled by time-variable magnetospheric electron densities.

  • 22.
    Menietti, J. D.
    et al.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Averkamp, T. F.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Ye, S. -Y
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Groene, J. B.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Extended Survey of Saturn Z-Mode Wave Intensity Through Cassini's Final Orbits2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 15, p. 7330-7336Article in journal (Refereed)
    Abstract [en]

    Similar to whistler mode chorus, Z-mode emission is an efficient diffusive scatterer of electrons possibly resulting in resonant acceleration. We present results of a survey of both the low-band (5 kHz) and for the first time the high-band (20 kHz) intensity of these emissions, based on over 11 years of Cassini Radio and Plasma Wave Science instrument data including nine ring-grazing orbits and two proximal orbits, which occurred at the end of the mission. We distinguish these emissions using density and polarization measurements and calculate the mean intensity as a function of frequency and spatial coordinates. We find that the average low-band Z-mode intensity peak is P-0 similar to 7 x 10(-8) nT(2), while the high-band peak is much lower at P-0 similar to 10(-9) nT(2). The spatial distribution of intensity differs for each emission band implying different source regions and perhaps different source mechanisms.

    Plain Language Summary

    Intense narrow band waves (Z-mode) are observed at Saturn when the spacecraft is located in regions of relatively low density and high magnetic field. These waves are of special importance because they are not seen at such high intensity or over as large a spatial range at Earth. In addition, these waves are known to be very efficient at accelerating electrons under certain conditions and could be responsible for a portion of the observed radiation belts at Saturn. We present an extensive survey of the observations of Z-mode extending over more than 11 years. The survey includes for the first time both the low and high-frequency emissions and orbits from the Cassini final mission, where these waves were seen at a high rate of occurrence. Contour plots and graphs of wave intensity as a function of radius, latitude, and longitude are shown, which will be of value to scientists who model the dynamic processes controlling the electron population at Saturn.

  • 23.
    Menietti, J. D.
    et al.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Averkamp, T. F.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Ye, S. -Y
    Sulaiman, A. H.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Hospodarsky, G. B.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Analysis of Intense Z-Mode Emission Observed During the Cassini Proximal Orbits2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 14, p. 6766-6772Article in journal (Refereed)
    Abstract [en]

    The role of Z-mode emission in the diffusive scattering and resonant acceleration of electrons is believed to be important at Saturn. A survey of the 5kHz component of this emission at Saturn earlier reported strong intensity in the lower density regions where the ratio of plasma frequency to cyclotron frequency, f(p)/f(c)<1. At Saturn this occurs along the inner edge of the Enceladus torus near the equator and at higher latitudes. Using the Cassini Radio and Plasma Wave Science instrument observations during the Cassini proximal orbits, we have now identified these emissions extending down to and within the ionosphere. Wave polarization measurements and unique frequency cutoffs are used to positively identify the wave mode. Analogous to the role of whistler mode chorus at Earth, Saturn Z-mode emissions may interact with electrons contributing to the filling or depleting of Saturn's inner radiation belts.

  • 24.
    Milillo, A.
    et al.
    INAF, Inst Space Astrophys & Planetol, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Fujimoto, M.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Murakami, G.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Benkhoff, J.
    ESA ESTEC, Sci & Operat Dept, Directorate Sci, Noordwijk, Netherlands..
    Zender, J.
    ESA ESTEC, Sci & Operat Dept, Directorate Sci, Noordwijk, Netherlands..
    Aizawa, S.
    Univ Toulouse, CNRS, Inst Rech Astrophys & Planetol, CNES, Toulouse, France..
    Dosa, M.
    Wigner Res Ctr Phys, Dept Space Res & Space Technol, Budapest, Hungary..
    Griton, L.
    Univ Toulouse, CNRS, Inst Rech Astrophys & Planetol, CNES, Toulouse, France..
    Heyner, D.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterrestr Phys, Braunschweig, Germany..
    Ho, G.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD 20723 USA..
    Imber, S. M.
    Univ Michigan, Dept Atmospher Ocean & Space Sci, Ann Arbor, MI 48109 USA.;Univ Leicester, Dept Phys & Astron, Space Res Ctr, Leicester, Leics, England..
    Jia, X.
    Karlsson, T.
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Space & Plasma Phys, Stockholm, Sweden..
    Killen, R. M.
    Goddard Space Flight Ctr, Greenbelt, MD USA..
    Laurenza, M.
    INAF, Inst Space Astrophys & Planetol, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Lindsay, S. T.
    Univ Leicester, Dept Phys & Astron, Space Res Ctr, Leicester, Leics, England..
    McKenna-Lawlor, S.
    Space Technol Ireland Ltd, Maynooth, Kildare, Ireland..
    Mura, A.
    INAF, Inst Space Astrophys & Planetol, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Raines, J. M.
    Univ Michigan, Dept Climate & Space Sci & Engn, Ocean & Space Sci, Ann Arbor, MI 48109 USA..
    Rothery, D. A.
    Open Univ, Sch Phys Sci, Milton Keynes, Bucks, England..
    Andre, N.
    Univ Toulouse, CNRS, Inst Rech Astrophys & Planetol, CNES, Toulouse, France..
    Baumjohann, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Berezhnoy, A.
    Moscow MV Lomonosov State Univ, Sternberg Astron Inst, Moscow, Russia.;Kazan Fed Univ, Inst Phys, Kazan, Russia..
    Bourdin, P. A.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.;Karl Franzens Univ Graz, Inst Phys, Graz, Austria..
    Bunce, E. J.
    Univ Leicester, Dept Phys & Astron, Space Res Ctr, Leicester, Leics, England..
    Califano, F.
    Univ Pisa, Pisa, Italy..
    Deca, J.
    Univ Colorado, Boulder, CO 80309 USA..
    de la Fuente, S.
    ESA ESAC, Villanueva De La Canada, Spain..
    Dong, C.
    Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544 USA.;Princeton Univ, Princeton Plasma Phys Lab, Princeton, NJ 08544 USA..
    Grava, C.
    SWRI, San Antonio, TX USA..
    Fatemi, S.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Henri, P.
    Univ Orleans, CNRS, Lab Phys & Chim Environm & Espace, CNES, Orleans, France..
    Ivanovski, S. L.
    INAF, Osservatorio Astron Trieste, Trieste, Italy..
    Jackson, B. V.
    Univ Calif San Diego, La Jolla, CA 92093 USA..
    James, M.
    Univ Leicester, Dept Phys & Astron, Space Res Ctr, Leicester, Leics, England..
    Kallio, E.
    Aalto Univ, Sch Elect Engn, Dept Elect & Nanoengn, Helsinki, Finland..
    Kasaba, Y.
    Tohoku Univ, Planetary Plasma & Atmospher Res Ctr, Sendai, Miyagi, Japan..
    Kilpua, E.
    Univ Helsinki, Dept Phys, Helsinki, Finland..
    Kobayashi, M.
    Chiba Inst Technol, Planetary Explorat Res Ctr, Narashino, Chiba, Japan..
    Langlais, B.
    Univ Angers, Univ Nantes, CNRS, Lab Planetol & Geodynam, Nantes, France..
    Leblanc, F.
    Sorbonne Univ, CNRS, LATMOS, IPSL, Paris, France..
    Lhotka, C.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Mangano, V.
    INAF, Inst Space Astrophys & Planetol, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Martindale, A.
    Univ Leicester, Dept Phys & Astron, Space Res Ctr, Leicester, Leics, England..
    Massetti, S.
    INAF, Inst Space Astrophys & Planetol, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Masters, A.
    Imperial Coll London, Blackett Lab, London, England..
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Narita, Y.
    Karl Franzens Univ Graz, Inst Phys, Graz, Austria..
    Oliveira, J. S.
    ESA ESTEC, Sci & Operat Dept, Directorate Sci, Noordwijk, Netherlands.;Univ Coimbra, CITEUC, Geophys & Astron Observ, Coimbra, Portugal..
    Odstrcil, D.
    Goddard Space Flight Ctr, Greenbelt, MD USA..
    Orsini, S.
    INAF, Inst Space Astrophys & Planetol, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Pelizzo, M. G.
    CNR, Inst Photon & Nanotechnol, Padua, Italy..
    Plainaki, C.
    Italian Space Agcy, Rome, Italy..
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Sahraoui, F.
    Seki, K.
    Univ Tokyo, Grad Sch Sci, Dept Earth & Planetary Sci, Tokyo, Japan..
    Slavin, J. A.
    Univ Michigan, Dept Atmospher Ocean & Space Sci, Ann Arbor, MI 48109 USA..
    Vainio, R.
    Univ Turku, Dept Phys & Astron, Space Res Lab, Turku, Finland..
    Wurz, P.
    Univ Bern, Phys Inst, Bern, Switzerland..
    Barabash, S.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Carr, C. M.
    Imperial Coll London, Dept Phys, London, England..
    Delcourt, D.
    Univ Orleans, Paris, France..
    Glassmeier, K. -H
    Grande, M.
    Univ Wales, Inst Math & Phys Sci, Aberystwyth, Dyfed, Wales..
    Hirahara, M.
    Nagoya Univ, Inst Space Earth Environm Res, Nagoya, Aichi, Japan..
    Huovelin, J.
    Univ Helsinki, Dept Phys, Helsinki, Finland..
    Korablev, O.
    IKI, Moscow, Russia..
    Kojima, H.
    Kyoto Univ, Res Inst Sustainable Humanosphere, Kyoto, Japan..
    Lichtenegger, H.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Livi, S.
    SWRI, San Antonio, TX USA..
    Matsuoka, A.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Moissl, R.
    ESA ESTEC, Sci & Operat Dept, Directorate Sci, Noordwijk, Netherlands..
    Moncuquet, M.
    Univ Paris Diderot, PSL Res Univ, Sorbonne Univ, LESIA,Observ Paris,CNRS,UPMC,Sorbonne Paris Cite, Meudon, France..
    Muinonen, K.
    Univ Helsinki, Dept Phys, Helsinki, Finland..
    Quemerais, E.
    Univ Versailles St Quentin, LATMOS, Guyancourt, France..
    Saito, Y.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Yagitani, S.
    Kanazawa Univ, Grad Sch Nat Sci & Technol, Kanazawa, Ishikawa, Japan..
    Yoshikawa, I.
    Univ Tokyo, Dept Complex Sci & Engn, Tokyo, Japan..
    Wahlund, J. -E
    Investigating Mercury's Environment with the Two-Spacecraft BepiColombo Mission2020In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 216, no 5, article id 93Article, review/survey (Refereed)
    Abstract [en]

    The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. Many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of Mercury as well as the complex processes that govern it. Many issues remain unsolved even after the MESSENGER mission that ended in 2015. The specific orbits of the two spacecraft, MPO and Mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. These joint observations are of key importance because many phenomena in Mercury's environment are highly temporally and spatially variable. Examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different BepiColombo instruments sensors.

    Download full text (pdf)
    FULLTEXT01
  • 25.
    Moore, L.
    et al.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA.
    Cravens, T. E.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Mueller-Wodarg, I.
    Imperial Coll London, Blackett Lab, London, England.
    Perry, M. E.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    Waite, J. H., Jr.
    Southwest Res Inst, San Antonio, TX USA.
    Perryman, R.
    Southwest Res Inst, San Antonio, TX USA.
    Nagy, A.
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA.
    Mitchell, D.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    Persoon, A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Wahlund, J. -E
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Models of Saturn's Equatorial Ionosphere Based on In Situ Data From Cassini's Grand Finale2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 18, p. 9398-9407Article in journal (Refereed)
    Abstract [en]

    We present new models of Saturn's equatorial ionosphere based on the first in situ measurements of its upper atmosphere. The neutral spectrum measured by Cassini's Ion and Neutral Mass Spectrometer, which includes substantial methane, ammonia, and organics in addition to the anticipated molecular hydrogen, helium, and water, serves as input for unexpectedly complex ionospheric chemistry. Heavy molecular ions are found to dominate Saturn's equatorial low-altitude ionosphere, with a mean ion mass of 11Da. Key molecular ions include H3O+ and HCO+; other abundant heavy ions depend upon the makeup of the mass 28 neutral species, which cannot be uniquely determined. Ion and Neutral Mass Spectrometer neutral species lead to generally good agreement between modeled and observed plasma densities, though poor reproduction of measured H+ and H-3(+) variability and an overabundance of modeled H-3(+) potentially hint at missing physical processes in the model, including a loss process that affects H-3(+) but not H+. Plain Language Summary Cassini's Grand Finale enabled the first-ever direct measurements of Saturn's upper atmosphere. Here we use Cassini's unique measurements to construct new models of the plasma in this important boundary region that separates the dense lower atmosphere from space. Based on the complex array of observed gases, we find that heavy molecular ions are dominant near Saturn's equator. This surprising result demonstrates that the chemistry in Saturn's equatorial upper atmosphere is substantially more complex than anticipated. The presence of these unexpected ions potentially represents a new method of monitoring Saturn's ionosphere remotely. Furthermore, as other Cassini measurements indicate that the complex chemistry is likely driven by an influx of ring-derived material, such observations may even help to track the evolution of Saturn's rings as they lose mass to its atmosphere.

  • 26.
    Morooka, Michiko W.
    et al.
    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.
    Andrews, David J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Ye, S. -Y
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Farrell, W. M.
    NASA, GSFC, Greenbelt, MD USA.
    The Dusty Plasma Disk Around the Janus/Epimetheus Ring2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 6, p. 4668-4678Article in journal (Refereed)
    Abstract [en]

    We report on the electron, ion, and dust number densities and the electron temperatures obtained by the Radio and Plasma Wave Science instruments onboard Cassini during the Ring-Grazing orbits. The numerous ring passage observations show a consistent picture as follows: (1) Beyond 0.1 R-S above and below the equator the electron and ion densities are quasi-neutral with a distribution similar to the one obtained in the plasma disk. (2) A sharp ion density enhancement occurs at vertical bar Z vertical bar < 0.1 R-S, to more than 200 cm(-3) at the equator, while the electron density remains low only to values of 50cm(-3). The electron/ion density ratio is <= 0.1 at the equator. (3) Micrometer-sized dust has also been observed at the equator. However, the region of intense dust signals is significantly narrower (vertical bar Z vertical bar<0.02 R-S) than the enhanced ion density regions. (4) The electron temperature (T-e) generally decreases with decreasing Z with small T-e enhancements near the equator. We show that the dust size characteristics are different depending on the distance from the equator, and the large micrometer-sized grains are more perceptible in a narrow region near the equator where the power law slope of the dust size distribution becomes less steep. As a result, different scale heights are obtained for nanometer and micrometer grains. Throughout the ring, the dominant part of the negative charges is carried by the small nanometer-sized grains. The electron/ion density ratio is variable from orbit to orbit, suggesting changes in the dust charging over time scales of weeks. Plain Language Summary The Radio and Plasma Wave Science instrument onboard Cassini observed a dusty plasma during the Ring-Grazing orbits. Dusty plasma is composed of, in addition to the electrons and ions, charged dust grains, and those grains play an important role in the plasma dynamics. The observed electron, ion, and dust number densities and the electron temperatures showed the layered structure of the faint Janus/Epimetheus rings. The core of the dusty ring composed of micron-sized dust is surrounded by a dusty plasma consisting of the ions and the negatively charged nanometer grains and further surrounded by the pristine plasma. The electron/ion density ratio of the dusty plasma varies from orbit to orbit, implying that the dust charging characteristics of the dusty ring change over time scales of weeks.

  • 27.
    Morooka, Michiko
    et al.
    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.
    Hadid, Lina Z.
    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.
    Vigren, Erik
    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.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Farrell, W. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Waite, J. H.
    Southwest Res Inst, San Antonio, TX USA.
    Perryman, R. S.
    Southwest Res Inst, San Antonio, TX USA.
    Perry, M.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    Saturn's Dusty Ionosphere2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 3, p. 1679-1697Article in journal (Refereed)
    Abstract [en]

    Measurements of electrons and ions in Saturn's ionosphere down to 1,500-km altitudes as well as the ring crossing region above the ionosphere obtained by the Langmuir probe onboard the Cassini spacecraft are presented. Five nearly identical deep ionosphere flybys during the Grand Finale orbits and the Final plunge orbit revealed a rapid increase in the plasma densities and discrepancies between the electrons and ions densities (N-e and N-i) near the closest approach. The small N-e/N-i ratio indicates the presence of a dusty plasma, a plasma which charge carrier is dominated by negatively charged heavy particles. Comparison of the Langmuir probe obtained density with the light ion density obtained by the Ion and Neutral Mass Spectrometer confirmed the presence of heavy ions. An unexpected positive floating potential of the probe was also observed when N-e/N-i << 1. This suggests that Saturn's ionosphere near the density peak is in a dusty plasma state consisting of negatively and positively charged heavy cluster ions. The electron temperature (T-e) characteristics in the ionosphere are also investigated and unexpectedly high electron temperature value, up to 5000 K, has been observed below 2,500-km altitude in a region where electron-neutral collisions should be prominent. A well-defined relationship between T-e and N-e/N-i ratio was found, implying that the electron heating at low altitudes is related to the dusty plasma state of the ionosphere.

  • 28.
    Persoon, A. M.
    et al.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Groene, J. B.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Smith, H. T.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Perry, M. E.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Swedish Inst Space Phys, Uppsala, Sweden..
    Ye, S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.;Southern Univ Sci & Technol, Dept Earth & Space Sci, Shenzhen, Peoples R China..
    Evidence of Electron Density Enhancements in the Post-Apoapsis Sector of Enceladus' Orbit2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 6, article id e2019JA027768Article in journal (Refereed)
    Abstract [en]

    Enceladus' plume is the dominant source of neutrals and plasma in Saturn's magnetosphere. The plasma results from the ionization of icy particles and water vapor, which are vented into Saturn's inner magnetosphere through fissures in Enceladus' southern polar region. These fissures are subjected to tidal stresses that can vary as Enceladus moves in a slightly eccentric orbit around Saturn. Plume activity and brightness have also been shown to vary with the moon's orbital position, reaching a maximum when Enceladus is farthest away from Saturn in its orbit (the Enceladus orbital apoapsis). In this paper we will show that temporal variations in the thermal electron density distribution correlate with the position of Enceladus in its orbit around Saturn, with the strongest density enhancements in the vicinity of Enceladus when the moon is in the post-apoapsis sector of its orbit.

  • 29.
    Shebanits, O.
    et al.
    Imperial Coll London, Blackett Lab, London, England..
    Hadid, L. Z.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Sweden.;ESA ESTEC, Noordwijk, Netherlands..
    Cao, H.
    Harvard Univ, Dept Earth & Planetary Sci, Cambridge, England.;CALTECH, Div Geol & Planetary Sci, Pasadena, CA 91125 USA..
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hunt, G. J.
    Imperial Coll London, Blackett Lab, London, England..
    Dougherty, M. K.
    Imperial Coll London, Blackett Lab, London, England..
    Wahlund, J-E
    Waite, J. H., Jr.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX USA..
    Muller-Wodarg, I
    Imperial Coll London, Blackett Lab, London, England..
    Saturn's near-equatorial ionospheric conductivities from in situ measurements2020In: Scientific Reports, E-ISSN 2045-2322, Vol. 10, no 1, article id 7932Article in journal (Refereed)
    Abstract [en]

    Cassini's Grand Finale orbits provided for the first time in-situ measurements of Saturn's topside ionosphere. We present the Pedersen and Hall conductivities of the top near-equatorial dayside ionosphere, derived from the in-situ measurements by the Cassini Radio and Wave Plasma Science Langmuir Probe, the Ion and Neutral Mass Spectrometer and the fluxgate magnetometer. The Pedersen and Hall conductivities are constrained to at least 10(-5)-10(-4) S/m at (or close to) the ionospheric peak, a factor 10-100 higher than estimated previously. We show that this is due to the presence of dusty plasma in the near-equatorial ionosphere. We also show the conductive ionospheric region to be extensive, with thickness of 300-800 km. Furthermore, our results suggest a temporal variation (decrease) of the plasma densities, mean ion masses and consequently the conductivities from orbit 288 to 292.

    Download full text (pdf)
    FULLTEXT01
  • 30.
    Shebanits, Oleg
    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.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Holmberg, Mika
    Université de Toulouse, UPS-OMP, IRAP, Toulouse, France.; CNRS, IRAP, Toulouse, France.
    Morooka, Michiko
    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.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Mandt, Kathleen
    Waite, Hunter
    Titan’s ionosphere: A survey of solar EUV influences2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 7, p. 7491-7503Article in journal (Refereed)
    Abstract [en]

    Effects of solar EUV on positive ions and heavy negative charge carriers (molecular ions, aerosol, and/or dust) in Titan’s ionosphere are studied over the course of almost 12 years, including 78 flybys below 1400 km altitude between TA (October 2004) and T120 (June 2016). The Radio and Plasma Wave Science/Langmuir Probe-measured ion charge densities (normalized by the solar zenith angle) show statistically significant variations with respect to the solar EUV flux. Dayside charge densities increase by a factor of ≈2 from solar minimum to maximum, while nightside charge densities are found to anticorrelate with the EUV flux and decrease by a factor of ≈3–4. The overall EUV dependence of the ion charge densities suggest inapplicability of the idealized Chapman theory below 1200 km in Titan’s ionosphere. Nightside charge densities are also found to vary along Titan’s orbit, with higher values in the sunward magnetosphere of Saturn compared to the magnetotail.

  • 31.
    Sulaiman, Ali H.
    et al.
    Univ Iowa, Iowa City, IA 52242 USA..
    Achilleos, Nicholas
    UCL, London, England..
    Bertucci, Cesar
    Univ Buenos Aires, Buenos Aires, DF, Argentina..
    Coates, Andrew
    Mullard Space Sci Lab, Dorking, Surrey, England.;UCL Birkbeck, Ctr Planetary Sci, London, England..
    Dougherty, Michele
    Imperial Coll London, London, England..
    Hadid, Lina
    Ecole Polytech, LPP, Palaiseau, France..
    Holmberg, Mika
    Inst Rech Astrophys & Planetol, Toulouse, France..
    Hsu, Hsiang-Wen
    Univ Colorado, Boulder, CO 80309 USA..
    Kimura, Tomoki
    Tokyo Univ Sci, Tokyo, Japan..
    Kurth, William
    Univ Iowa, Iowa City, IA 52242 USA..
    Le Gall, Alice
    Univ Versailles St Quentin, LATMOS, Versailles, France..
    McKevitt, James
    Mullard Space Sci Lab, Dorking, Surrey, England.;Univ Vienna, Vienna, Austria..
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Murakami, Go
    Japan Aerosp Explorat Agcy, Tokyo, Japan..
    Regoli, Leonardo
    Johns Hopkins Appl Phys Lab, Laurel, MD USA..
    Roussos, Elias
    Max Planck Inst Solar Syst Res, Gottingen, Germany..
    Saur, Joachim
    Univ Cologne, Cologne, Germany..
    Shebanits, Oleg
    Japan Aerosp Explorat Agcy, Tokyo, Japan..
    Solomonidou, Anezina
    CALTECH, Pasadena, CA 91125 USA..
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Waite, J. Hunter
    Southwest Res Inst, San Antonio, TX USA..
    Enceladus and Titan: emerging worlds of the Solar System2022In: Experimental astronomy, ISSN 0922-6435, E-ISSN 1572-9508, Vol. 54, no 2-3, p. 849-876Article in journal (Refereed)
    Abstract [en]

    Some of the major discoveries of the recent Cassini-Huygens mission have put Titan and Enceladus firmly on the Solar System map. The mission has revolutionised our view of Solar System satellites, arguably matching their scientific importance with that of their host planet. While Cassini-Huygens has made big surprises in revealing Titan's organically rich environment and Enceladus' cryovolcanism, the mission's success naturally leads us to further probe these findings. We advocate the acknowledgement of Titan and Enceladus science as highly relevant to ESA's long-term roadmap, as logical follow-on to Cassini-Huygens. In this White Paper, we will outline important science questions regarding these satellites and identify the science themes we recommend ESA cover during the Voyage 2050 planning cycle. Addressing these science themes would make major advancements to the present knowledge we have about the Solar System, its formation, evolution, and likelihood that other habitable environments exist outside the Earth's biosphere.

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  • 32.
    Taylor, S. A.
    et al.
    Univ Coll London, Mullard Space Sci Lab, Dorking, Surrey, England; UCL Birkbeck, Ctr Planetary Sci, London, England.
    Coates, A. J.
    Univ Coll London, Mullard Space Sci Lab, Dorking, Surrey, England; UCL Birkbeck, Ctr Planetary Sci, London, England.
    Jones, G. H.
    Univ Coll London, Mullard Space Sci Lab, Dorking, Surrey, England; UCL Birkbeck, Ctr Planetary Sci, London, England.
    Wellbrock, A.
    Univ Coll London, Mullard Space Sci Lab, Dorking, Surrey, England; UCL Birkbeck, Ctr Planetary Sci, London, England.
    Fazakerley, A. N.
    Univ Coll London, Mullard Space Sci Lab, Dorking, Surrey, England.
    Desai, R. T.
    Univ Coll London, Mullard Space Sci Lab, Dorking, Surrey, England; UCL Birkbeck, Ctr Planetary Sci, London, England.
    Caro-Carretero, R.
    Univ Coll London, Mullard Space Sci Lab, Dorking, Surrey, England; Univ Pontificia Comillas, Escuela Tecn Super Ingn ICAI, Madrid, Spain.
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Schippers, P.
    Observ Paris, LESIA, Meudon, France.
    Waite, J. H.
    Southwest Res Inst, San Antonio, TX USA.
    Modeling, Analysis, and Interpretation of Photoelectron Energy Spectra at Enceladus Observed by Cassini2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 287-296Article in journal (Refereed)
    Abstract [en]

    The Electron Spectrometer (ELS) of the Cassini Plasma Spectrometer has observed photoelectrons produced in the plume of Enceladus. These photoelectrons are observed during Enceladus encounters in the energetic particle shadow where the spacecraft is largely shielded from penetrating radiation by the moon. We present a complex electron spectrum at Enceladus including evidence of two previously unidentified electron populations at 6–10 eV and 10–16 eV. We estimate that the proportion of “hot” (>15 eV) to “cold” (<15 eV) electrons during the Enceladus flybys is ≈ 0.1–0.5%. We have constructed a model of photoelectron production in the plume and compared it with ELS Enceladus flyby data by scaling and energy shifting according to spacecraft potential. We suggest that the complex structure of the electron spectrum observed can be explained entirely by photoelectron production in the plume ionosphere.

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  • 33.
    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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  • 34.
    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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  • 35.
    Wahlund, Jan-Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Morooka, Michiko W
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hadid, Lina Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Farrell, W. M.
    NASA Goddard Space Flight Ctr, Solar Syst Explorat Div, Greenbelt, MD 20771 USA..
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Hospodarsky, G.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Ye, S. -Y
    Andrews, David J.
    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.
    Vigren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    In situ measurements of Saturn's ionosphere show that it is dynamic and interacts with the rings2018In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 359, no 6371, p. 66-68Article in journal (Refereed)
    Abstract [en]

    The ionized upper layer of Saturn's atmosphere, its ionosphere, provides a closure of currents mediated by the magnetic field to other electrically charged regions (for example, rings) and hosts ion-molecule chemistry. In 2017, the Cassini spacecraft passed inside the planet's rings, allowing in situ measurements of the ionosphere. The Radio and Plasma Wave Science instrument detected a cold, dense, and dynamic ionosphere at Saturn that interacts with the rings. Plasma densities reached up to 1000 cubic centimeters, and electron temperatures were below 1160 kelvin near closest approach. The density varied between orbits by up to two orders of magnitude. Saturn's A- and B-rings cast a shadow on the planet that reduced ionization in the upper atmosphere, causing a north-south asymmetry.

  • 36.
    Waite, J. H., Jr.
    et al.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX 78238 USA.
    Perryman, R. S.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX 78238 USA.
    Perry, M. E.
    Johns Hopkins Univ, Appl Phys Lab, Johns Hopkins Rd, Laurel, MD 20723 USA.
    Miller, K. E.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX 78238 USA.
    Bell, J.
    Natl Inst Aerosp, Hampton, VA 23666 USA;NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Cravens, T. E.
    Univ Kansas, Dept Phys & Astron, Lawrence, KS 66045 USA.
    Glein, C. R.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX 78238 USA.
    Grimes, J.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX 78238 USA.
    Hedman, M.
    Univ Idaho, Dept Phys, Moscow, ID 83844 USA.
    Cuzzi, J.
    NASA, Ames Res Ctr, Moffett Field, CA 94035 USA.
    Brockwell, T.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX 78238 USA.
    Teolis, B.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX 78238 USA.
    Moore, L.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA.
    Mitchell, D. G.
    Johns Hopkins Univ, Appl Phys Lab, Johns Hopkins Rd, Laurel, MD 20723 USA.
    Persoon, A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Wahlund, Jan-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.
    Hadid, Lina Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Chocron, S.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX 78238 USA.
    Walker, J.
    Southwest Res Inst, Space Sci & Engn Div, San Antonio, TX 78238 USA.
    Nagy, A.
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA.
    Yelle, R.
    Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA.
    Ledvina, S.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.
    Johnson, R.
    Univ Virginia, Dept Mat Sci & Engn, Charlottesville, VA 22904 USA.
    Tseng, W.
    Natl Taiwan Normal Univ, Dept Earth Sci, Taipei 11677, Taiwan.
    Tucker, O. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Ip, W. -H
    Chemical interactions between Saturn's atmosphere and its rings2018In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 362, no 6410, article id eaat2382Article in journal (Refereed)
    Abstract [en]

    The Pioneer and Voyager spacecraft made close-up measurements of Saturn's ionosphere and upper atmosphere in the 1970s and 1980s that suggested a chemical interaction between the rings and atmosphere. Exploring this interaction provides information on ring composition and the influence on Saturn's atmosphere from infalling material. The Cassini Ion Neutral Mass Spectrometer sampled in situ the region between the D ring and Saturn during the spacecraft's Grand Finale phase. We used these measurements to characterize the atmospheric structure and material influx from the rings. The atmospheric He/H-2 ratio is 10 to 16%. Volatile compounds from the rings (methane; carbon monoxide and/or molecular nitrogen), as well as larger organic-bearing grains, are flowing inward at a rate of 4800 to 45,000 kilograms per second.

  • 37.
    Xystouris, Georgios
    et al.
    Univ Lancaster, Phys Dept, Lancaster LA1 4YB, England..
    Arridge, Christopher S.
    Univ Lancaster, Phys Dept, Lancaster LA1 4YB, England..
    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.
    Estimating the optical depth of Saturn's main rings using the Cassini Langmuir Probe2023In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 526, no 4, p. 5839-5860Article in journal (Refereed)
    Abstract [en]

    A Langmuir Probe (LP) measures currents from incident charged particles as a function of the applied bias voltage. While onboard a spacecraft the particles are either originated from the surrounding plasma, or emitted (e.g. through photoemission) from the spacecraft itself. The obtained current-voltage curve reflects the properties of the plasma in which the probe is immersed into, but also any photoemission due to illumination of the probe surface: As photoemission releases photoelectrons into space surrounding the probe, these can be recollected and measured as an additional plasma population. This complicates the estimation of the properties of the ambient plasma around the spacecraft. The photoemission current is sensitive to the extreme ultraviolet (UV) part of the spectrum, and it varies with the illumination from the Sun and the properties of the LP surface material, and any variation in the photoelectrons irradiance can be measured as a change in the current voltage curve. Cassini was eclipsed multiple times by Saturn and the main rings over its 14 yr mission. During each eclipse the LP recorded dramatic changes in the current-voltage curve, which were especially variable when Cassini was in shadow behind the main rings. We interpret these variations as the effect of spatial variations in the optical depth of the rings and hence use the observations to estimate the optical depth of Saturn's main rings. Our estimates are comparable with UV optical depth measurements from Cassini's remote sensing instruments.

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  • 38. Ye, S. -Y
    et al.
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Hospodarsky, G. B.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Persoon, A. M.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Sulaiman, A. H.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
    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.
    Hsu, H. -W
    Sternovsky, Z.
    Univ Colorado, LASP, Boulder, CO 80309 USA.
    Wang, X.
    Univ Colorado, LASP, Boulder, CO 80309 USA.
    Horanyi, M.
    Univ Colorado, LASP, Boulder, CO 80309 USA.
    Seiss, M.
    Univ Potsdam, Inst Phys & Astron, Potsdam, Germany.
    Srama, R.
    Univ Stuttgart, Inst Space Syst IRS, Stuttgart, Germany.
    Dust Observations by the Radio and Plasma Wave Science Instrument During Cassini's Grand Finale2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 19, p. 10101-10109Article in journal (Refereed)
    Abstract [en]

    Dust particles in the Saturn system can be detected by the Radio and Plasma Wave Science (RPWS) instrument on board Cassini via antenna voltage signals induced by dust impacts. These impact signals have been simulated in the laboratory by accelerating dust particles onto a Cassini model with electric field antennas. RPWS dust measurements have been shown to be consistent with the Cosmic Dust Analyzer. During the Grand Finale orbits, Cassini flew through the gap between the D ring and Saturn's atmosphere 22 times. In situ measurements by RPWS helped quantify the hazards posed to the spacecraft and instruments on board, which showed a micron-sized dust density orders of magnitude lower than that observed during the Ring Grazing orbits. Close inspection of the waveforms indicated a possible dependence of the impact signal decay time on ambient plasma density. Plain Language Summary Cassini flew through the gap between Saturn and its rings for 22 times before plunging into the atmosphere of Saturn, ending its 20-year mission. The radio and plasma waves instrument on board Cassini helped quantify the dust hazard in this previously unexplored region. The measured density of large dust particles was much lower than expected, allowing high-value science observations during the subsequent Grand Finale orbits.

  • 39.
    Zaslavsky, A.
    et al.
    Sorbonne Univ, Univ PSL, Univ Paris, Observ Paris,LESIA,CNRS, Paris, France..
    Mann, I
    Arctic Univ Norway, Inst Phys & Technol, Tromso, Norway..
    Soucek, J.
    Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic..
    Czechowski, A.
    Polish Acad Sci, Space Res Ctr, Warsaw, Poland..
    Pisa, D.
    Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic..
    Vaverka, J.
    Charles Univ Prague, Fac Math & Phys, Prague, Czech Republic..
    Meyer-Vernet, N.
    Sorbonne Univ, Univ PSL, Univ Paris, Observ Paris,LESIA,CNRS, Paris, France..
    Maksimovic, M.
    Sorbonne Univ, Univ PSL, Univ Paris, Observ Paris,LESIA,CNRS, Paris, France..
    Lorfevre, E.
    CNES, 18 Ave Edouard Belin, F-31400 Toulouse, France..
    Issautier, K.
    Sorbonne Univ, Univ PSL, Univ Paris, Observ Paris,LESIA,CNRS, Paris, France..
    Babic, K. Rackovic
    Sorbonne Univ, Univ PSL, Univ Paris, Observ Paris,LESIA,CNRS, Paris, France.;Univ Belgrade, Fac Math, Dept Astron, Belgrade, Serbia..
    Bale, S. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Phys Dept, Berkeley, CA USA..
    Morooka, Michiko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vecchio, A.
    Sorbonne Univ, Univ PSL, Univ Paris, Observ Paris,LESIA,CNRS, Paris, France.;Radboud Univ Nijmegen, Dept Astrophys, Radboud Radio Lab, Nijmegen, Netherlands..
    Chust, T.
    Sorbonne Univ, Univ Paris Saclay, Observ Paris, Ecole Polytech,LPP,CNRS, Paris, France..
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Krasnoselskikh, V
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;LPC2E, CNRS, 3A Ave Rech Sci, Orleans, France..
    Kretzschmar, M.
    LPC2E, CNRS, 3A Ave Rech Sci, Orleans, France.;Univ Orleans, Orleans, France..
    Plettemeier, D.
    Tech Univ Dresden, Wurzburger Str 35, D-01187 Dresden, Germany..
    Steller, M.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Stverak, S.
    Czech Acad Sci, Inst Atmospher Phys, Prague, Czech Republic.;Czech Acad Sci, Astron Inst, Prague, Czech Republic..
    Travnicek, P.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Czech Acad Sci, Astron Inst, Prague, Czech Republic..
    Vaivads, A.
    Royal Inst Technol, Sch Elect Engn & Comp Sci, Space & Plasma Phys, Stockholm, Sweden..
    First dust measurements with the Solar Orbiter Radio and Plasma Wave instrument2021In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 656, article id A30Article in journal (Refereed)
    Abstract [en]

    Context. Impacts of dust grains on spacecraft are known to produce typical impulsive signals in the voltage waveform recorded at the terminals of electric antennas. Such signals (as may be expected) are routinely detected by the Time Domain Sampler (TDS) system of the Radio and Plasma Waves (RPW) instrument on board Solar Orbiter.

    Aims. We investigate the capabilities of RPW in terms of interplanetary dust studies and present the first analysis of dust impacts recorded by this instrument. Our purpose is to characterize the dust population observed in terms of size, flux, and velocity.

    Methods. We briefly discuss previously developed models of voltage pulse generation after a dust impact onto a spacecraft and present the relevant technical parameters for Solar Orbiter RPW as a dust detector. Then we present the statistical analysis of the dust impacts recorded by RPW /TDS from April 20, 2020 to February 27, 2021 between 0.5AU and 1AU.

    Results. The study of the dust impact rate along Solar Orbiter's orbit shows that the dust population studied presents a radial velocity component directed outward from the Sun. Its order of magnitude can be roughly estimated as nu(r,dust) similar or equal to 50 km s(-1), which is consistent with the flux of impactors being dominated by fi-meteoroids. We estimate the cumulative flux of these grains at 1AU to be roughly F-beta similar or equal to 8 x 10(-5) m(-2) s(-1) for particles of a radius r greater than or similar to 100 nm. The power law index ffi of the cumulative mass flux of the impactors is evaluated by two di fferents methods, namely: direct observations of voltage pulses and indirect e ffect on the impact rate dependency on the impact speed. Both methods give the following result: delta similar or equal to 0.3-0.4.

    Conclusions. Solar Orbiter RPW proves to be a suitable instrument for interplanetary dust studies, and the dust detection algorithm implemented in the TDS subsystem an e fficient tool for fluxes estimation. These first results are promising for the continuation of the mission, in particular, for the in situ study of the inner Solar System dust cloud outside of the ecliptic plane, which Solar Orbiter will be the first spacecraft to explore.

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