Journal article
Observations of Energized Electrons in the Martian Magnetosheath
Journal of geophysical research. Space physics, Vol.126(4), e2020JA028984
04/2021
DOI: 10.1029/2020JA028984
Abstract
This observational study demonstrates that the magnitude and location of energization of electrons in the Martian magnetosheath is more complex than previous studies suggest. Electrons in Mars's magnetosheath originate in the solar wind and are accelerated by an electric field when they cross the bow shock. Assuming that this acceleration is localized solely to the shock, the field‐aligned electron distributions in the sheath are expected to be highly asymmetric. However, such an asymmetry is not observed in this study. Based on the analysis here, it is suggested that an additional parallel acceleration takes place downstream of the Martian bow shock. This additional acceleration suppresses the expected asymmetry of the electron distribution. Consequently, along a flux tube in the magnetosheath that is tied on both ends to the bow shock the difference in energization between parallel and anti‐parallel electrons is less than about 20 eV. Where this energization difference is expected to be maximal, we find the energization difference to be at most ≲25% of the predicted value.
Plain Language Summary
As the supersonic solar wind plasma encounters an obstacle, it is first slowed down to subsonic speeds and then diverted around the object. At the shock wave ahead of a planet, called the planet's “bow shock," individual electrons are accelerated by and electric field within the shock. These energized electrons move quickly along the local magnetic field from one side of the bow shock to the other. Downstream of the bow shock, the two electron populations moving in opposite directions along the magnetic field line should then have crossed the bow shock at the two locations where the field line meets the shock. Since the amount of energy gained by electrons is in general different at the two crossing locations, the two streaming electron populations observed downstream of the bow shock are expected to be energized by different amounts. On the contrary, this study identifies that away from the shock the two populations appear to have been energized very similarly. This may imply an additional acceleration downstream of the bow shock is required. This paper suggests two viable mechanisms that could explain the observations.
Key Points
The energization of electrons crossing the Martian bow shock can be described in terms of a quasi‐static localized potential drop
The energy difference of electrons entering the Martian bow shock at opposite locations on the same flux tube is much less than expected
A global, distributed potential within the sheath could resolve the unexpected trends reported in this work
Details
- Title: Subtitle
- Observations of Energized Electrons in the Martian Magnetosheath
- Creators
- K. Horaites - Laboratory for Atmospheric and Space PhysicsL. Andersson - Laboratory for Atmospheric and Space PhysicsS. J. Schwartz - Laboratory for Atmospheric and Space PhysicsS. Xu - Space Sciences LaboratoryD. L. Mitchell - Space Sciences LaboratoryC. Mazelle - Université de ToulouseJ. Halekas - University of IowaJ. Gruesbeck - Goddard Space Flight Center
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.126(4), e2020JA028984
- DOI
- 10.1029/2020JA028984
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Number of pages
- 17
- Grant note
- National Aeronautics and Space Administration MAVEN project
- Language
- English
- Date published
- 04/2021
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984428811202771
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