Abstract
Context. The Mutual Impedance Probe (RPC-MIP) carried by the Rosetta spacecraft monitored both the plasma density and the electric field in the close environment of comet 67P/Churyumov–Gerasimenko (67P), as the instrument was operating alternatively in two main modes: active and passive. The active mode is used primarily to perform plasma density measurements, while the passive mode enables the instrument to work as a wave analyzer. Aims. We are reporting electric field emissions at the plasma frequency near comet 67P observed by RPC-MIP passive mode. The electric field emissions are related to Langmuir waves within the cometary ionized environment. In addition, this study gives feedback on the density measurement capability of RPC-MIP in the presence of cold electrons. Methods. We studied the occurrence rate of the electric field emissions as well as their dependence on solar wind structures like stream interaction regions (SIRs) and coronal mass ejections (CMEs). Results. We are showing that strong electric field emissions at the plasma frequency near 67P were present sporadically throughout the period when Rosetta was escorting the comet, without being continuous, as the occurrence rate is reported to be of about 1% of all the measured RPC-MIP passive spectra showing strong electric field emissions. The Langmuir wave activity monitored by RPC-MIP showed measurable enhancements during SIR or CME interactions and near perihelion. Conclusions. According to our results, Langmuir waves are a common feature at 67P during the passage of SIRs. Comparing the plasma frequency given by the RPC-MIP passive mode during Langmuir wave periods with the RPC-MIP active mode observations, we conclude that the measurement accuracy of RPC-MIP depends on the operational submode when the cold electron component dominates the electron density.
Highlights
The European Space Agency (ESA) Rosetta mission escorted a comet, 67P/Churyumov–Gerasimenko (67P), for the first time along its path around the Sun and monitored its plasma environment between years 2014 and 2016
The goals of this paper are (i) to report the electric field observations of the Rosetta Plasma Consortium (RPC)-MIP instrument as the Rosetta orbiter was monitoring the cometary plasma of comet 67P, and (ii) to characterize and map the Langmuir waves measured in the cometary plasma
We studied electric field emissions at the plasma frequency near comet 67P observed by the RPC-MIP instrument on board the Rosetta spacecraft
Summary
The European Space Agency (ESA) Rosetta mission escorted a comet, 67P/Churyumov–Gerasimenko (67P), for the first time along its path around the Sun and monitored its plasma environment between years 2014 and 2016. Rosetta was carrying five instruments designed to study the near-comet plasma and electromagnetic field environment, the Rosetta Plasma Consortium (RPC; Carr et al 2007). One of the RPC instruments, the Mutual Impedance Probe (RPC-MIP; Trotignon et al 2007), had the primary task of estimating the near-comet plasma density. The Hermean magnetosphere will be studied by the Active Measurement of Mercury’s Plasma (AM2P; Trotignon et al 2006) instrument as part of the Plasma Wave Investigation (PWI; Kasaba et al 2020) on board BepiColombo (Milillo et al 2020). The Mutual Impedance Measurement (MIME) will be part of the Radio and Plasma Wave Investigation (RPWI) carried by the Jupiter ICy Moons Explorer (JUICE; Grasset et al 2013) mission that will observe plasma properties in the Jovian system
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