Ion velocity distributions at a low-activity comet: observations and interpretation
Anja Möslinger
Swedish Institute of Space Physics
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Abstract.
Comets are among the most diverse objects in the solar system. Their individual properties, such as size, composition, and activity, vary greatly. A specific comet's activity also changes significantly throughout its journey in the solar system. At its aphelion, far beyond Jupiter's orbit, the comet is almost idle due to the low solar irradiation. As the comet approaches the Sun, the increasing strength of the solar irradiation increases the activity of the comet, until it reaches its maximum near perihelion. Due to this variable environment, the interaction between the cometary plasma and the solar wind can take on many different shapes. While the large-scale physical processes at different activity processes are sufficiently well known, many questions about the behaviour at different activity levels still remain. The details of this interaction at a low activity comet are the focus of our study. Using data from the Rosetta mission to comet 67P, we analyse the velocity distribution of cometary and solar wind ions on April 19th, 2016. Their particular shape — resembling partial rings in this special case — allows us to extract the bulk properties of the different plasma populations. This gives us information about the entire interaction region at the comet. The results are complementary to the local plasma parameters provided by in-situ measurements of the spacecraft. We also derive estimates for the average electric fields at the comet at two different spatial scales. Measurements of the (quasi-)static electric fields are difficult to obtain using in-situ measurements of a single spacecraft and, in the case of comet 67P, are therefore usually only accessible in models.
Created 2022-12-12 08:46:36 by Mats Holmström Last changed 2023-01-18 18:40:03 by Mats Holmström
