Magnetic field draping enhancement at Mars, Venus and comets

BERTUCCI, C.; MAZELLE, C.; ACUÑA, M.; SAUER, K.; WINTERHALTER, D.

Congreso; EGS - AGU - EUG Joint Assembly; 2003

The absence of an intrinsic magnetic field at Mars, Venus and comets makes their interaction with the solar wind to exhibit many similarities. Among these, the formation of a magnetic barrier in front of a highly conducting obstacle and an induced magnetic tail are the most characteristic peculiarities. At Mars and comets, a sharp plasma boundary that represents the outer edge of the magnetic barrier, the Magnetic Pileup Boundary (MPB), has been identified by very clear observational signatures, including a gradient in the magnetic field magnitude (frequently observed as a sharp jump) accompanied by a decrease in the magnetic field fluctuations, and a simultaneous drastic decrease in the solar wind electron and proton densities, as the exospheric-induced ions begin to dominate. Recently, an analysis of the 3-D magnetic field topology in the surroundings of the Martian MPB using Mars Global Surveyor magnetometer data has also revealed a sudden enhancement of the field line draping exactly at the boundary. This feature appears to be a ubiquitous characteristic of this boundary, even when there is no obvious signature on the magnetic field magnitude. We apply the same technique to magnetometer data acquired near comets and Venus to show that this enhancement of draping is a commonplace for all weakly magnetized atmospheric bodies. As a corollary, we propose for the first time a mean to find the location of the counterpart of the MPB at Venus. Despite numerous studies on the Venusian magnetic barrier, such boundary has never been reported since there is usually no clear signature on the magnetic field magnitude.