Plasma characterization at comet 67P between 2 and 4 AU from the Sun with the RPC-MIP instrument

¹ Laboratoire Plasma et Conversion d’Energie (LAPLACE), Université de Toulouse, CNRS, 31062 Toulouse, France
e-mail: gaetan.wattieaux@laplace.univ-tlse.fr
² Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), CNRS, 45071 Orléans, France
³ Laboratoire Lagrange, OCA, CNRS, UCA, Nice, France
⁴ Laboratory for Atmospheric and Space Physics (LASP), University of Colorado Boulder 3665 Discovery Drive, Boulder, CO 80303, USA
⁵ Institute for Modeling Plasma, Atmospheres and Cosmic Dust, NASA/SSERVI, CA 94035, USA
⁶ Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles à Saint Quentin, 78280 Guyancourt, France

Received: 24 January 2020
Accepted: 30 April 2020

Abstract

The plasma of comet 67P/Churyumov-Gerasimenko is analyzed based on the RPC-MIP mutual impedance probe data of the Rosetta mission. Numerical simulations of the RPC-MIP instrumental response considering two populations of electrons were fit on experimental responses acquired from January to September 2016 to extract the electron densities and temperatures. A time-tracking of the plasma parameters was performed, leading to the identification of a cold and a warm population of electrons during the period of interest. The respective densities and temperatures lie in the ranges [100; 1000] cm⁻³ and [0.05; 0.3] eV for the cold electrons and in the ranges [50; 500] cm⁻³ and [2; 10] eV for the warm electrons. Warm electrons most of the time made up between 10 and 30% of the whole population, while the temperature ratio between warm and cold electrons lay mostly between 30 and 70 during the period we studied. The fluctuation range of the plasma parameters, that is, the electron densities and temperatures, appears to have remained rather constant during the last nine months of the mission. We take the limitations of the instrument that are due to the experimental noise into account in our discussion of the results.