Ion acoustic waves near a comet nucleus: Rosetta observations at comet 67P/Churyumov–Gerasimenko
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Published:2021-01-15
Issue:1
Volume:39
Page:53-68
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ISSN:1432-0576
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Container-title:Annales Geophysicae
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language:en
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Short-container-title:Ann. Geophys.
Author:
Gunell HerbertORCID, Goetz Charlotte, Odelstad EliasORCID, Beth Arnaud, Hamrin MariaORCID, Henri Pierre, Johansson Fredrik L., Nilsson HansORCID, Stenberg Wieser GabriellaORCID
Abstract
Abstract. Ion acoustic waves were observed between 15 and 30 km from the centre
of comet 67P/Churyumov–Gerasimenko by the Rosetta spacecraft during
its close flyby on 28 March 2015. There are two electron populations:
one cold at kBTe≈0.2 eV and one
warm at kBTe≈2 eV. The ions are
dominated by a cold (a few hundredths of electronvolt) distribution of
water group ions with a bulk speed of (3–3.7) km s−1. A
warm kBTe≈6 eV ion population,
which also is present, has no influence on the ion acoustic waves due
to its low density of only 0.25 % of the plasma density.
Near closest approach the propagation direction was within
50∘ from the direction of the bulk velocity. The waves, which
in the plasma frame appear below the ion plasma frequency
fpi≈2 kHz, are Doppler-shifted to the
spacecraft frame where they cover a frequency range up to
approximately 4 kHz.
The waves are detected in a region of space where the
magnetic field is piled up and draped around the inner part of the
ionised coma. Estimates of the current associated with the magnetic
field gradient as observed by Rosetta are used as input to
calculations of dispersion relations for current-driven ion acoustic
waves, using kinetic theory. Agreement between theory and observations
is obtained for electron and ion distributions with the properties
described above. The wave power decreases over cometocentric
distances from 24 to 30 km. The main difference between the
plasma at closest approach and in the region where the waves are
decaying is the absence of a significant current in the latter. Wave
observations and theory combined supplement the particle measurements
that are difficult at low energies and complicated by spacecraft
charging.
Funder
Swedish National Space Agency Centre National d’Etudes Spatiales European Space Agency
Publisher
Copernicus GmbH
Subject
Space and Planetary Science,Earth and Planetary Sciences (miscellaneous),Atmospheric Science,Geology,Astronomy and Astrophysics
Reference56 articles.
1. Acton, C. H.: Ancillary data services of NASA's Navigation and Ancillary
Information Facility, Planet. Space Sci., 44, 65–70,
https://doi.org/10.1016/0032-0633(95)00107-7, 1996. a 2. André, M., Odelstad, E., Graham, D. B., Eriksson, A. I., Karlsson, T.,
Stenberg Wieser, G., Vigren, E., Norgren, C., Johansson, F. L.,
Henri, P., Rubin, M., and Richter, I.: Lower hybrid waves at comet
67P/Churyumov-Gerasimenko, Mon. Not. R. Astron.
Soc., 469, 29–38, https://doi.org/10.1093/mnras/stx868, 2017. a 3. Berčič, L., Behar, E., Nilsson, H., Nicolaou, G., Stenberg Wieser,
G., Wieser, M., and Goetz, C.: Cometary ion dynamics observed in the close
vicinity of comet 67P/Churyumov-Gerasimenko during the intermediate
activity period, Astron. Astrophys., 613, A57,
https://doi.org/10.1051/0004-6361/201732082, 2018. a 4. Bergman, S., Stenberg Wieser, G., Wieser, M., Johansson, F. L., and Eriksson,
A.: The Influence of Spacecraft Charging on Low‐Energy Ion Measurements
Made by RPC-ICA on Rosetta, J. Geophys. Res.-Space, 125,
e2019JA027478, https://doi.org/10.1029/2019JA027478, 2020a. a 5. Bergman, S., Stenberg Wieser, G., Wieser, M., Johansson, F. L., and Eriksson,
A.: The Influence of Varying Spacecraft Potentials and Debye Lengths on In
Situ Low-Energy Ion Measurements, J. Geophys. Res.-Space, 125,
e2020JA027870, https://doi.org/10.1029/2020JA027870, 2020b. a
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