Publications
166 results found
Nilsson H, Behar E, Burch JL, et al., 2021, Birth of a Magnetosphere, MAGNETOSPHERES IN THE SOLAR SYSTEM, Editors: Maggiolo, Andre, Hasegawa, Welling, Zhang, Paxton, Publisher: AMER GEOPHYSICAL UNION, Pages: 427-439, ISBN: 978-1-119-50752-9
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Carnielli G, Galand M, Leblanc F, et al., 2020, Simulations of ion sputtering at Ganymede, Icarus, Vol: 351, Pages: 1-11, ISSN: 0019-1035
Ganymede's surface is subject to constant bombardment by Jovian magnetospheric and Ganymede's ionospheric ions. These populations sputter the surface and contribute to the replenishment of the moon's exosphere.Thus far, estimates for sputtering on the moon's surface have included only the contribution from Jovian ions. In this work, we have used our recent model of Ganymede's ionosphere Carnielli et al., 2019 to evaluate the contribution of ionospheric ions for the first time. In addition, we have made new estimates for the contribution from Jovian ions, including both thermal and energetic components.For Jovian ions, we find a total sputtering rate of 2.2 × 1027 s−1, typically an order of magnitude higher compared to previous estimates. For ionospheric ions, produced through photo- and electron-impact ionization, we find values in the range 2.7 × 1026–5.2 × 1027 s−1 when the moon is located above the Jovian plasma sheet. Hence, Ganymede's ionospheric ions provide a contribution of at least 10% to the sputtering rate, and under certain conditions they dominate the process. This finding indicates that the ionospheric population is an important source to consider in the context of exospheric models.
Stephenson P, Galand M, Deca J, et al., 2020, Cooling of Electrons in a Weakly Outgassing Comet
<jats:p>&lt;p&gt;The plasma instruments, Mutual Impedance Probe (MIP) and Langmuir Probe (LAP), part of the Rosetta Plasma Consortium (RPC), onboard the Rosetta mission to comet 67P revealed a population of cold electrons (&lt;1eV) (Engelhardt et al., 2018; Wattieaux et al, 2020; Gilet et al., 2020). This population is primarily generated by cooling warm (~10eV) newly-born cometary electrons through collisions with the neutral coma. What is surprising is that the cold electrons were detected throughout the escort phase, even at very low outgassing rates (Q&lt;1e26 s&lt;sup&gt;-1&lt;/sup&gt;) at large heliocentric distances (&gt;3 AU), when the coma was not thought to be dense enough to cool the electron population significantly.&lt;/p&gt;&lt;p&gt;&amp;#160;Using a collisional test particle model, we examine the behaviour of electrons in the coma of a weakly outgassing comet and the formation of a cold population through electron-neutral collisions. The model incorporates three electron sources: the solar wind, photo-electrons produced through ionisation of the cometary neutrals by extreme ultraviolet solar radiation, and secondary electrons produced through electron-impact ionisation.&lt;/p&gt;&lt;p&gt;The model includes different electron-water collision processes, including elastic, excitation, and ionisation collisions.&lt;/p&gt;&lt;p&gt;&amp;#160;The electron trajectories are shaped by electric and magnetic fields, which are taken from a 3D collisionless fully-kinetic Particle-in-Cell (PIC) model of the solar wind and cometary plasma&amp;#160; (Deca 2017, 2019). We use a spherically symmetric coma of pure water, which gives a r&lt;sup&gt;-2&lt;/sup&gt; profile in the neutral density. Throughout their lifetime, electrons undergo stochast
Beth A, Altwegg K, Balsiger H, et al., 2020, ROSINA ion zoo at Comet 67P, Astronomy and Astrophysics: a European journal, Vol: 642, Pages: 1-23, ISSN: 0004-6361
Context. The Rosetta spacecraft escorted Comet 67P/Churyumov-Gerasimenko for 2 yr along its journey through the Solar System between 3.8 and 1.24 au. Thanks to the high resolution mass spectrometer on board Rosetta, the detailed ion composition within a coma has been accurately assessed in situ for the very first time.Aims. Previous cometary missions, such as Giotto, did not have the instrumental capabilities to identify the exact nature of the plasma in a coma because the mass resolution of the spectrometers onboard was too low to separate ion species with similar masses. In contrast, the Double Focusing Mass Spectrometer (DFMS), part of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis on board Rosetta (ROSINA), with its high mass resolution mode, outperformed all of them, revealing the diversity of cometary ions.Methods. We calibrated and analysed the set of spectra acquired by DFMS in ion mode from October 2014 to April 2016. In particular, we focused on the range from 13–39 u q−1. The high mass resolution of DFMS allows for accurate identifications of ions with quasi-similar masses, separating 13C+ from CH+, for instance.Results. We confirm the presence in situ of predicted cations at comets, such as CHm+ (m = 1−4), HnO+ (n = 1−3), O+, Na+, and several ionised and protonated molecules. Prior to Rosetta, only a fraction of them had been confirmed from Earth-based observations. In addition, we report for the first time the unambiguous presence of a molecular dication in the gas envelope of a Solar System body, namely CO2++.
Galand M, Feldman PD, Bockelee-Morvan D, et al., 2020, Far-ultraviolet aurora identified at comet 67P/ Churyumov-Gerasimenko, Nature Astronomy, Vol: 4, Pages: 1084-1091, ISSN: 2397-3366
Having a nucleus darker than charcoal, comets are usually detected from Earth through the emissions from their coma. The coma is an envelope of gas that forms through the sublimation of ices from the nucleus as the comet gets closer to the Sun. In the far-ultraviolet portion of the spectrum, observations of comae have revealed the presence of atomic hydrogen and oxygen emissions. When observed over large spatial scales as seen from Earth, such emissions are dominated by resonance fluorescence pumped by solar radiation. Here, we analyse atomic emissions acquired close to the cometary nucleus by the Rosetta spacecraft and reveal their auroral nature. To identify their origin, we undertake a quantitative multi-instrument analysis of these emissions by combining coincident neutral gas, electron and far-ultraviolet observations. We establish that the atomic emissions detected from Rosetta around comet 67P/Churyumov-Gerasimenko at large heliocentric distances result from the dissociative excitation of cometary molecules by accelerated solar-wind electrons (and not by electrons produced from photo-ionization of cometary molecules). Like the discrete aurorae at Earth and Mars, this cometary aurora is driven by the interaction of the solar wind with the local environment. We also highlight how the oxygen line O I at wavelength 1,356 Å could be used as a tracer of solar-wind electron variability.
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