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D.A. Brain, J.S. Halekas, R.P. Lin, J.G. Luhmann, D.L. Mitchell, G.T. Delory, R.J. Lillis, M.O. Fillingim (UC Berkeley Space Sciences Lab), M.H. Acuna (NASA GSFC)
Recently reported observations of auroral emission at Mars provide dramatic evidence that charged particles from the solar wind have direct access to the Martian atmosphere. The Mars Express SPICAM instrument detected emission on the night side of the planet, in a cusp region near strong crustal magnetic fields. Auroral emission at Earth is known to be caused by electrons from the solar wind accelerated along open magnetic field lines. We report nearly 13,000 observations of accelerated electron features based on observations from the Mars Global Surveyor MAG/ER experiment. The long duration of the MGS mapping orbit allows us to both analyze individual acceleration events in detail and develop a statistical picture of the conditions and locations for which auroral acceleration is observed. We find that accelerated electrons are observed on both open and closed field lines near crustal magnetic sources, typically near magnetic cusp regions. External conditions control whether acceleration is likely to be observed by MGS, including the orientation of the solar wind magnetic field, solar wind pressure, and the orientation of Mars with respect to the solar wind flow (suggesting that there are auroral `seasons' on Mars). MGS often observes acceleration features near the optical shadow of Mars. Accelerated electrons are often associated with magnetic field rotations and electromagnetic wave activity in MGS data, which give clues about the mechanism responsible for their acceleration. If the accelerated electrons MGS observes are associated with optical emissions, our results imply that the emission observed by Mars Express, while not commonplace, can often be observed on the Martian nightside.
This work has been supported by NASA MDAP grant NNG04GL35G.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.