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

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.

Simultaneously Formed Wedge‐Like Structures of Different Ion Species Deep in the Inner Magnetosphere

“…1. Attributing total densities in excess of 500 cm −3 to cold electrons gives relative abundances of the latter in the range 0 − 75%, roughly in line with preliminary estimates by (some) previous authors [Gilet et al, 2017;Engelhardt et al, 2018;Gilet et al, 2020;Wattieaux et al, 2020]. The electron gyro-radius is r Le ∼ 400 − 800 m (for T e ∼ 5 eV).…”

Observations of a mix of cold and warm electrons by RPC-MIP at 67P/Churyumov-Gerasimenko

“…This is well modeled and reported in Wattieaux et al (2019), that developed a model of the mutual impedance response taking into account the effect of the spacecraft charging on the mutual impedance measurement. By fitting the in situ mutual impedance spectra to a dataset of modeled mutual impedance spectra in a two-electron temperature plasma, it has been shown that it is possible to detect the presence of cold electrons even when the double resonance is not visible on the mutual impedance spectra (Wattieaux et al 2020).…”

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

“…This process was repeated every 160 s. Each of the two probes obtained 295 such time series during the day. The power spectral density for each time series is computed, using Welch's method (Welch, 1967), averaging segments that are 256 samples long with an overlap of 65 % (Fig. 2a and b).…”