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The Structure of Martian Magnetosphere at the Dayside Terminator Region as Observed on MAVEN Spacecraft
Journal article   Peer reviewed

The Structure of Martian Magnetosphere at the Dayside Terminator Region as Observed on MAVEN Spacecraft

O. L Vaisberg, V. N Ermakov, S. D Shuvalov, L. M Zelenyi, J Halekas, G. A DiBraccio, J McFadden and E. M Dubinin
Journal of geophysical research. Space physics, Vol.123(4), pp.2679-2695
04/2018
DOI: 10.1002/2018JA025202
url
https://arxiv.org/pdf/1801.08878View
Open Access

Abstract

We analyzed 44 passes of the Mars Atmosphere and Volatile EvolutioN mission (MAVEN) spacecraft through the magnetosphere, arranged by the angle between electric field vector and the projection of spacecraft position radius vector in the plane perpendicular to the Mars‐Sun line (θE). All passes were divided into three angular sectors near 0°, 90°, and 180° θE angles in order to estimate the role of the interplanetary magnetic field direction in plasma and magnetic properties of dayside Martian magnetosphere. The time interval chosen was from 17 January to 4 February 2016 when MAVEN was crossing the dayside magnetosphere at solar zenith angle ~70°. Magnetosphere as the region with prevailing energetic planetary ions is always found between the magnetosheath and the ionosphere. The analysis of dayside interaction region showed that for each angular sector with different orientation of the solar wind electric field vector E = −1/c V × B one can find specific profiles of the magnetosheath, the magnetic barrier (Michel, 1971, https://doi.org/10.1029/RG009i002p00427; Zhang et al., 1991, https://doi.org/10.1029/91JA00088), and the magnetosphere. Magnetic barrier forms in front of the magnetosphere, and relative magnetic field magnitudes in these two domains vary. The average height of the boundary with ionosphere is ~530 km, and the average height of the magnetopause is ~730 km. We discuss the implications of the observed magnetosphere structure to the planetary ions loss mechanism. Plain Language Summary As Mars does not have an intrinsic global magnetic field, the solar wind directly interacts with the gaseous envelope of Mars. This interaction leads to formation of the magnetosphere from magnetic field tubes of the solar wind that bend around the planet forming magnetoplasma envelope around it. The dayside of the magnetosphere was not studied in detail due to its relatively small scale. MAVEN spacecraft with its comprehensive payload gives possibility for studying the dayside magnetosphere of Mars. Analysis of MAVEN plasma and magnetic measurements showed that the dayside Martian magnetosphere is a permanent layer of the magnetized plasma between heated solar wind plasma flow and the ionosphere. With average thickness of ~200 km it is filled with planetary ions accumulated during convection of these tubes from the dayside to the tail. These ions then escape through the tail being the one of the primary loss sources that led to devastating the Martian atmosphere through millennia. It is found that the magnetic structure and planetary ion flux in dayside magnetosphere are asymmetric to what is determined by the direction of the interplanetary magnetic field. This asymmetry is analyzed in the paper. Key Points The dayside magnetosphere of Mars at ~70° SZA is a permanent domain of ~200 km thickness between the magnetosheath and the ionosphere Magnetopause is defined by a steep gradient of O+ and O2+ densities, which increase by factor of 102–103 at interface with the ionosphere The structure of the dayside magnetosphere is controlled by directions of solar wind magnetic field and solar wind motional electric field
 magnetosphere Mars planetary ions solar wind

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