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D.A. Brain, F. Bagenal (LASP / CU), M.H. Acuna, J.E.P. Connerney (NASA GSFC)
It is possible that strong crustal magnetic fields at Mars form "mini-magnetospheres" that protect the Martian atmosphere in certain regions. As a result, the extent of magnetic influence of the Martian crust has important consequences for atmospheric evolution and the energetics of the upper atmosphere. We employ two approaches to describe the altitude to which crustal magnetic sources modify the interaction of the solar wind with Mars, and show animations of the shape of the Martian solar wind obstacle.
First, MGS MAG data from pre-mapping orbits are examined. Using altitude profiles of the data in log-log space, we observe a change in the profile slope at an altitude where the crust no longer directly affects observations. This "transition altitude" is determined as a function of planetary position at a resolution of 10 degrees, and we give the resulting map depicting the altitude of influence of the Martian crust.
Second, we use one model for Martian crustal magnetism to compute the shape of the Martian obstacle to the solar wind. The obstacle that a planetary body presents to the solar wind is usually considered to be the location where solar wind dynamic pressure is balanced by pressure contributions from the planet. At Mars the situation is complicated over that at Venus and comets by crustal sources, which provide a magnetic pressure contribution in addition to planetary ionospheric thermal pressure. The Martian solar wind obstacle, then, is not smooth like the obstacles at Venus and comets, and has time variability that depends upon planetary rotation. We use a magnetic field model for Mars to calculate the pressure balance surface for a variety of solar wind dynamic pressures, and will show animations of the obstacle shape as Mars rotates.