MERCURYS MAGNETOSPHERE - ANOTHER LOOK

The measurements made of Mercury's magnetic field during the Mercury I flyby and the Mercury III flyby have been incorporated into models of the Hermean magnetosphere-magnetotail system. When the magnetic field data for the first half of the Mercury I flyby and all of the Mercury III flyby were incorporated pinto a single fit of a scaled version of the Beard (J. Geophys. Res. 84, 2118-2122, 1979) Earth magnetosphere- magnetotail system, a r.m.s. deviation of 9.3 nT for-the magnetic fiel d vector was obtained (Bergan and Engle, J. Geophys. Res. 86, 1617-162 0, 1981). This paper presents results of a study that employs an adapt ation of that Beard model but also adopts the assumption that the inci dent solar wind pressure was different at the times of the two Mercury magnetosphere encounters. Resulting different standoff distances and scaling factors for the data of the two respective flybys result direc tly from that single assumption. The study yields a comparable fit of reduced r.m.s. deviation of 7.1 nT and a strength of the Mercury plane tary dipole moment D (before any displacement effects are incorporated ) between 154 nT R(M)(3) (Merc 1) and 182 nT R(M)(3), (Merc 3). The co rresponding standoff distances are 1.31 R(M) for the Merc 3 encounter and 1.08 R(M) for the Merc 1 encounter. (C) 1997 Published by Elsevier Science Ltd.