Abstract
The Mars Express Analyzer of Space Plasmas and Energetic Atoms experiment contains ion and electron instruments for conducting plasma measurements. On January 23, 2012, during in-bound travel of Mars Express in the southern hemisphere of Mars from its dawn side toward periapsis at dusk, the plasma instruments measured foreshock-like ion beams extending from outside the bow shock and into the magnetosphere, continuing to a distance of about a proton gyroradius from the bow shock. These ion beams were mostly protons, were observed to have energies greater than solar wind protons, and were not gyrating, in agreement with reflections of the solar wind proton beam. Furthermore, in the foreshock region the ion energy gradually decreased toward the magnetosheath, in agreement with an acceleration by outward-directed electric field in the bowshock. The observations also suggest that this electric field exists even inside the magnetosheath within the distance of a proton gyroradius from the bow shock.
Highlights
The solar wind forms a magnetospheric cavity around Mars
Since the flow directions of these foreshock-like ions are narrowly distributed and relatively constant (Fig. 4), and since we know that the interplanetary magnetic field (IMF) is draped around the planet, so we estimate the IMF direction in the magnetosheath to be the direction of solar wind ion flow where we used the electron observations to determine the region of the magnetosheath
This paper presented foreshock-like ions which were observed in both the foreshock region and in the magnetosheath, there have been some observations of ions in the foreshock region which are not observed in the magnetosheath
Summary
The solar wind forms a magnetospheric cavity around Mars. This magnetosphere results from an induced interaction of the solar wind with the upper atmosphere of Mars. The upper atmosphere of Mars ionizes and creates an ionosphere where currents flow to create the induced magnetic field This causes the solar wind to be deflected around the planet. Part of the solar wind interaction that creates the bow shock can create a foreshock region of reflected and accelerated electrons and ions. Separation between the electron and ion foreshock regions are related to the angle between the IMF and bow shock normal. It has been found at the Earth that this angle is less than 90° for electrons and less than 70° for ions, which is suggested by Burgess (1995) to be due to the acceleration mechanism for ions being less efficient than for electrons; the details may depend on the size and shape of the bow shock.
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