The Solar Wind interaction with Mars: locations and shapes of the Bow Shock and the Magnetic Pile-up Boundary from the observations of the MAG/ER experiment onboard Mars Global Surveyor

The Mars Global Surveyor spacecraft, was inserted into an elliptical orbit around Mars on September 12, 1997. It includes the MAG/ER instrument with t wo magnetometers providing in-situ sensing of the ambient magnetic field an d an electron reflectometer measuring the local distribution function of th e electrons in the energy range of 10 eV to 20 keV. This statistical study deals With the identification and the position of the Bow Shock (BS) and of another plasma boundary, the Magnetic Pile-up Boundary (MPB), proved as pe rmanent by MAG/ER. During the first year of the MGS mission, a total of 290 orbits have been considered to fit the-geometric characteristics of these boundaries. The position and shape of these boundaries are compared with pr evious studies.:Good agreement is found with the Phobos 2 observations, sug gesting than the mean bow shock and MPB locations are independent of solar cycle phase. The great number of crossings shows-that-the Bow Shock positio n and nightside MPB position are highly variable.