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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/angeo-2020-59
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2020-59
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  18 Aug 2020

18 Aug 2020

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This preprint is currently under review for the journal ANGEO.

Ion acoustic waves near a comet nucleus: Rosetta observations at comet 67P/Churyumov-Gerasimenko

Herbert Gunell1, Charlotte Götz2, Elias Odelstad3, Arnaud Beth1, Maria Hamrin1, Pierre Henri4,5, Fredrik L. Johansson6, Hans Nilsson7, and Gabriella Stenberg Wieser7 Herbert Gunell et al.
  • 1Department of Physics, Umeå University, 901 87 Umeå, Sweden
  • 2Space Research and Technology Centre, European Space Agency, Keplerlaan 1, 2201AZ Noordwijk, The Netherlands
  • 3Department of Space and Plasma Physics, Royal Institute of Technology, 100 44 Stockholm, Sweden
  • 4LPC2E, CNRS, F-45071 Orléans, France
  • 5Lagrange, OCA, CNRS, UCA, Nice, France
  • 6Swedish Institute of Space Physics, Box 537, 751 21 Uppsala, Sweden
  • 7Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden

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 approximately 0.2 eV and one warm at approximately 4 eV. The ions are dominated by a cold (a few hundredths of eV) distribution with a bulk speed of (3–3.7) km/s. Near closest approach the propagation direction was within 50 degrees from the direction of the bulk velocity, leading to a Doppler shift of the waves that in the spacecraft frame cover a frequency range up to approximately 4 kHz. The wave power decreased 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.

Herbert Gunell et al.

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Herbert Gunell et al.

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Latest update: 23 Nov 2020
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Short summary
When the magnetised solar wind meets the plasma surrounding a comet, the magnetic field is enhanced in front of the comet and the field lines are draped around it. This happens because electric currents are induced in the plasma. When these currents flow through the plasma, they can generate waves. In this article we present observations of ion acoustic waves, which is a kind of sound waves in a plasma, detected by instruments on the Rosetta spacecraft near comet 67P/Churyumov-Gerasimenko.
When the magnetised solar wind meets the plasma surrounding a comet, the magnetic field is...
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