Messenger Observations Of Mercury\u27S Exosphere: Detection Of Magnesium And Distribution Of Constituents

Abstract

Mercury is surrounded by a tenuous exosphere that is supplied primarily by the planet\u27s surface materials and is known to contain sodium, potassium, and calcium. Observations by the Mercury Atmospheric and Surface Composition Spectrometer during MESSENGER\u27s second Mercury flyby revealed the presence of neutral magnesium in the tail (anti-sunward) region of the exosphere, as well as differing spatial distributions of magnesium, calcium, and sodium atoms in both the tail and the nightside, near-planet exosphere. Analysis of these observations, supplemented by observations during the first Mercury flyby, as well as those by other MESSENGER instruments, suggests that the distinct spatial distributions arise from a combination of differences in source, transfer, and loss processes. © 2009 by the American Association for the Advancement of Science