uu.seUppsala University Publications
Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 97) Show all publications
Deca, J., Henri, P., Divin, A., Eriksson, A., Galand, M., Beth, A., . . . Horanyi, M. (2019). Building a Weakly Outgassing Comet from a Generalized Ohm's Law. Physical Review Letters, 123(5), Article ID 055101.
Open this publication in new window or tab >>Building a Weakly Outgassing Comet from a Generalized Ohm's Law
Show others...
2019 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 5, article id 055101Article in journal (Refereed) Published
Abstract [en]

When a weakly outgassing comet is sufficiently close to the Sun, the formation of an ionized coma results in solar wind mass loading and magnetic field draping around its nucleus. Using a 3D fully kinetic approach, we distill the components of a generalized Ohm's law and the effective electron equation of state directly from the self-consistently simulated electron dynamics and identify the driving physics in the various regions of the cometary plasma environment. Using the example of space plasmas, in particular multispecies cometary plasmas, we show how the description for the complex kinetic electron dynamics can be simplified through a simple effective closure, and identify where an isotropic single-electron fluid Ohm's law approximation can be used, and where it fails.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-393346 (URN)10.1103/PhysRevLett.123.055101 (DOI)000479003800007 ()
Funder
The European Space Agency (ESA), 4000119035/16/ES/JD
Available from: 2019-09-27 Created: 2019-09-27 Last updated: 2019-09-27Bibliographically approved
Volwerk, M., Goetz, C., Behar, E., Delva, M., Edberg, N. J. T., Eriksson, A., . . . Glassmeier, K.-H. (2019). Dynamic field line draping at comet 67P/Churyumov-Gerasimenko during the Rosetta dayside excursion. Astronomy and Astrophysics, 630, Article ID A44.
Open this publication in new window or tab >>Dynamic field line draping at comet 67P/Churyumov-Gerasimenko during the Rosetta dayside excursion
Show others...
2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A44Article in journal (Refereed) Published
Abstract [en]

Context: The Rosetta dayside excursion took place in September-October 2015 when comet 67P/Churyumov-Gerasimenko (67P/CG) was located at similar to 1.36 AU from the Sun after it had passed perihelion on 13 August 2015 at similar to 1.25 AU. At this time, the comet was near its most active period, and its interaction with the solar wind was expected to be at its most intense, with ion pickup and magnetic field line draping. The dayside excursion was planned to move through different regions that were expected upstream of the cometary nucleus, and to possibly detect the location of the bow shock.

Aims: The goal of this study is to describe the dynamic field line draping that takes place around the comet and the plasma processes that are connected to this.

Methods: The data from the full Rosetta Plasma Consortium (RPC) were used to investigate the interaction of solar wind and comet, starting from boxcar-averaged magnetic field data in order to suppress high-frequency noise in the data. Through calculating the cone and clock angle of the magnetic field, we determined the draping pattern of the magnetic field around the nucleus of the comet. Then we studied the particle data in relation to the variations that are observed in the magnetic field.

Results: During the dayside excursion, the magnetic field cone angle changed several times, which means that the magnetic field direction changes from pointing sunward to anti-sunward. This is caused by the changing directions of the interplanetary magnetic field that is transported toward the comet. The cone-angle direction shows that mass-loading of the interplanetary magnetic field of the solar wind leads to dynamic draping. The ion velocity and the magnetic field strength are correlated because the unmagnetized ions are accelerated more (less) strongly by the increasing (decreasing) magnetic field strength. There is an indication of an anticorrelation between the electron density and the magnetic field strength, which might be caused by the magnetized electrons being mirrored out of the strong field regions. The Rosetta RPC has shown that (dynamic) draping also occurs as mildly active comets, as was found at highly active comets such as 1P/Halley and 21P/Giacobini-Zinner, but also that determining both dynamic and nested draping will require a combination of fast flybys and slow excursions for future missions.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2019
Keywords
comets: individual: 67P/Churyumov-Gerasimenko, magnetic fields, plasmas, methods: data analysis
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-395685 (URN)10.1051/0004-6361/201935517 (DOI)000486989400043 ()
Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-10-24Bibliographically approved
Goldstein, R., Burch, J. L., Llera, K., Mokashi, P., Nilsson, H., Dokgo, K., . . . Richter, I. (2019). Electron acceleration at comet 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics, 630, Article ID A40.
Open this publication in new window or tab >>Electron acceleration at comet 67P/Churyumov-Gerasimenko
Show others...
2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A40Article in journal (Refereed) Published
Abstract [en]

We report the observation by the Ion and Electron Sensor (IES) of energetic (>1 keV) electrons in the plasma environment of comet 67P Churyumov-Gerasimenko (67P). Most of the electrons in the cometary coma are expected to be of solar wind, photoionization, or electron impact origin and are therefore not expected to exceed some hundreds of eV in energy. During the Vega flybys of comet Halley, 1 keV electrons were also observed, and these are explained as having been accelerated by lower hybrid (LH) waves resulting from the two-stream instability involving the solar wind and pickup-ion flows. These waves resonate with the cyclotron motion of the ions and the longitudinal motion of electrons and are on the order of several Hz, at least in the case of 67P. We postulate that the energetic electrons we have observed intermittently during December 2015 through January 2016 are also the result of such a process and that Landau damping causes the acceleration and subsequent abrupt decrease in this energy (also seen at Halley). We show from this study an event on 19 January 2016 when IES simultaneously observed accelerated electrons, solar wind protons, water ions, and LH waves. A dispersion analysis shows that the ion-ion two-stream instability has positive growth rates for such waves during the observation period.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2019
Keywords
plasmas, waves, methods: data analysis, comets: individual: 67P/Churyumov-Gerasimenko
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-395681 (URN)10.1051/0004-6361/201834701 (DOI)000486989400039 ()
Funder
Swedish National Space Board
Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-10-24Bibliographically approved
Mandt, K. E., Eriksson, A., Beth, A., Galand, M. & Vigren, E. (2019). Influence of collisions on ion dynamics in the inner comae of four comets. Astronomy and Astrophysics, 630, Article ID A48.
Open this publication in new window or tab >>Influence of collisions on ion dynamics in the inner comae of four comets
Show others...
2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A48Article in journal (Refereed) Published
Abstract [en]

Context: Collisions between cometary neutrals in the inner coma of a comet and cometary ions that have been picked up into the solar wind flow and return to the coma lead to the formation of a broad inner boundary known as a collisionopause. This boundary is produced by a combination of charge transfer and chemical reactions, both of which are important at the location of the collisionopause boundary. Four spacecraft measured ion densities and velocities in the inner region of comets, exploring the part of the coma where an ion-neutral collisionopause boundary is expected to form.

Aims: The aims are to determine the dominant physics behind the formation of the ion-neutral collisionopause and to evaluate where this boundary has been observed by spacecraft.

Methods: We evaluated observations from three spacecraft at four different comets to determine if a collisionopause boundary was observed based on the reported ion velocities. We compared the measured location of the ion-neutral collisionopause with measurements of the collision cross sections to evaluate whether chemistry or charge exchange are more important at the location where the collisionopause is observed.

Results: Based on measurements of the cross sections for charge transfer and for chemical reactions, the boundary observed by Rosetta appears to be the location where chemistry becomes the more probable result of a collision between H2O and H2O+ than charge exchange. Comparisons with ion observations made by Deep Space 1 at 19P/Borrelly and Giotto at 1P/Halley and 26P/Grigg-Skjellerup show that similar boundaries were observed at 19P/Borrelly and 1P/Halley. The ion composition measurements made by Giotto at Halley confirm that chemistry becomes more important inside of this boundary and that electron-ion dissociative recombination is a driver for the reported ion pileup boundary.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2019
Keywords
molecular processes, plasmas, comets: individual: 67P/Churyumov-Gerasimenko, comets: individual: 1P/Halley, comets: individual: 19P/Borelly, comets: individual: 26P/Grigg-Skjellerup
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-395683 (URN)10.1051/0004-6361/201834828 (DOI)000486989400047 ()
Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-10-24Bibliographically approved
Vigren, E. & Eriksson, A. I. (2019). On the ion-neutral coupling in cometary comae. Monthly notices of the Royal Astronomical Society, 482(2), 1937-1941
Open this publication in new window or tab >>On the ion-neutral coupling in cometary comae
2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 482, no 2, p. 1937-1941Article in journal (Refereed) Published
Abstract [en]

In a cometary coma, the ion-neutral decoupling distance, sometimes referred to as the ion exobase or collisionopause, can be defined as the cometocentric distance, r(in), where ions, initially moving with the neutral outgassing speed, have a probability of 1/e of not colliding with neutrals on their subsequent journey radially outwards. We present an analytical model for calculating this decoupling distance in the presence of a static radial electric field. We show that for a logarithmically decaying potential, the value of r(in) can even decrease to similar to 15 per cent of its field-free case value. Moreover, already at this distance, the effective ion speed can be expected to markedly exceed the neutral expansion velocity. These analytical results are in line with previous numerical calculations, adapting similar but not identical field profiles. The presence of a non-negligible ambipolar electric field and limited importance of ion-neutral collisional coupling are further supported by observations in the diamagnetic cavity of comet 67P/Churyumov-Gerasimenko by plasma instruments onboard Rosetta that reveal ion speeds several times higher than the neutral expansion velocity.

Keywords
molecular processes, comets (general)
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-374113 (URN)10.1093/mnras/sty2869 (DOI)000454578700037 ()
Available from: 2019-01-23 Created: 2019-01-23 Last updated: 2019-01-23Bibliographically approved
Myllys, M., Henri, P., Galand, M., Heritier, K. L., Gilet, N., Goldstein, R., . . . Deca, J. (2019). Plasma properties of suprathermal electrons near comet 67P/Churyumov-Gerasimenko with Rosetta. Astronomy and Astrophysics, 630, Article ID A42.
Open this publication in new window or tab >>Plasma properties of suprathermal electrons near comet 67P/Churyumov-Gerasimenko with Rosetta
Show others...
2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A42Article in journal (Refereed) Published
Abstract [en]

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

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

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

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

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

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2019
Keywords
methods: data analysis, comets: general, plasmas
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-395684 (URN)10.1051/0004-6361/201834964 (DOI)000486989400041 ()
Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-10-24Bibliographically approved
Breuillard, H., Henri, P., Bucciantini, L., Volwerk, M., Karlsson, T., Eriksson, A., . . . Hajra, R. (2019). Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission. Astronomy and Astrophysics, 630, Article ID A39.
Open this publication in new window or tab >>Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission
Show others...
2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A39Article in journal (Refereed) Published
Abstract [en]

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

Keywords
comets: general, comets: individual: 67P/Churyumov-Gerasimenko, plasmas, waves, methods: observational, methods: data analysis
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-395801 (URN)10.1051/0004-6361/201834876 (DOI)000486989400038 ()
Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-10-25Bibliographically approved
Morooka, M., Wahlund, J.-E., Hadid, L. Z., Eriksson, A. I., Edberg, N. J. T., Vigren, E., . . . Perry, M. (2019). Saturn's Dusty Ionosphere. Journal of Geophysical Research - Space Physics, 124(3), 1679-1697
Open this publication in new window or tab >>Saturn's Dusty Ionosphere
Show others...
2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 3, p. 1679-1697Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2019
Keywords
Saturn's ionosphere, dusty plasma, Langmuir probe, plasma density, electron temperature
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-387566 (URN)10.1029/2018JA026154 (DOI)000466087900016 ()
Funder
Swedish Research Council, 621-2013-4191Swedish Research Council, 2.2.1-312/16Swedish National Space Board, Dnr 174/15 135/13 162/14
Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-06-24Bibliographically approved
Hadid, L. Z., Morooka, M. W., Wahlund, J.-E., Persoon, A. M., Andrews, D. J., Shebanits, O., . . . Eriksson, A. I. (2019). Saturn's Ionosphere: Electron Density Altitude Profiles and D-Ring Interaction From The Cassini Grand Finale. Geophysical Research Letters, 46(16), 9362-9369
Open this publication in new window or tab >>Saturn's Ionosphere: Electron Density Altitude Profiles and D-Ring Interaction From The Cassini Grand Finale
Show others...
2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 16, p. 9362-9369Article in journal (Refereed) Published
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.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-396547 (URN)10.1029/2018GL078004 (DOI)000490966700007 ()
Funder
Swedish National Space BoardSwedish Research Council, 2016-05364Swedish National Space Board, Dnr 174/15Swedish National Space Board, Dnr 135/13Swedish Research Council, 621-2013-4191
Available from: 2019-11-07 Created: 2019-11-07 Last updated: 2019-11-07Bibliographically approved
Edberg, N. J. T., Johansson, F., Eriksson, A., Andrews, D. J., Hajra, R., Henri, P., . . . Thiemann, E. (2019). Solar flares observed by Rosetta at comet 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics, 630, Article ID A49.
Open this publication in new window or tab >>Solar flares observed by Rosetta at comet 67P/Churyumov-Gerasimenko
Show others...
2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A49Article in journal (Refereed) Published
Abstract [en]

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

Keywords
plasmas, space vehicles: instruments, Sun: flares, comets: general
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-395802 (URN)10.1051/0004-6361/201834834 (DOI)000486989400048 ()
Funder
Swedish National Space Board, 109/12Swedish National Space Board, 135/13Swedish Research Council, 621-2013-4191Swedish Research Council, 621-2014-5526
Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-10-25Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2926-6761

Search in DiVA

Show all publications