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D.A. Brain, F. Bagenal (CU / LASP), M.H. Acuña, J.E.P. Connerney (NASA GSFC), D.L. Mitchell (UCB / SSI)
The Mars Global Surveyor (MGS) magnetometer (MAG) has determined that Mars is unique in its interaction with the solar wind. It falls among the class of solar system bodies that rely on their atmospheres to deflect the solar wind, but, unlike similar bodies, has regions of significant crustal magnetization. Magnetometers on spacecraft orbiting Mars can expect to measure field contributions from both the solar wind and the Martian crust; the MGS MAG data provide an unprecendented chance to study the relevant importance of these contributions. Starting in September of 1997, MGS spent eighteen months in an elliptical orbit ideally suited for study of the solar wind interaction with Mars. Since June of 1999 MGS has been in a nearly circular 400 km mapping orbit well-suited for thorough examination of the influence of crustal fields at that altitude.
We explore the MAG data to investigate the control of certain parameters (local time, solar zenith angle, altitude, and latitude/longitude) on characteristics of the magnetic field. We demonstrate that solar wind strongly affects observations at high altitudes and on the dayside of the planet. The solar wind influence is greatest at local times near noon. The Martian crust strongly affects observations at low altitudes and on the planetary nightside, though its influence can be detected as high as 700 km above some regions of the surface. We give evidence for the existence of closed field lines at low altitude over crustal sources. These regions may contain trapped electron populations observed by the MGS electron reflectometer.
Finally, we compare MAG data with a recent model of the Martian surface field [Purucker et al., GRL 27, p. 2449, 2000] to determine where and under what conditions this model is consistent with observations.
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