Title

Limits to Mercury's magnesium exosphere from MESSENGER second flyby observations

Authors

Authors

M. Sarantos; R. M. Killen; W. E. McClintock; E. T. Bradley; R. J. Vervack; M. Benna;J. A. Slavin

Comments

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Abbreviated Journal Title

Planet Space Sci.

Keywords

Mercury; Mercury atmosphere; Mercury surface; Atmospheric structure; Mercury magnetosphere; MESSENGER; SODIUM; MODEL; IMPACT; MAGNETOSPHERE; VAPORIZATION; ATMOSPHERE; LUNAR; NAO; Astronomy & Astrophysics

Abstract

The discovery measurements of Mercury's exospheric magnesium, obtained by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) probe during its second Mercury flyby, are modeled to constrain the source and loss processes for this neutral species. Fits to a Chamberlain exosphere reveal that at least two source temperatures are required to reconcile the distribution of magnesium measured far from and near the planet: a hot ejection process at the equivalent temperature of several tens of thousands of degrees K, and a competing, cooler source at temperatures as low as 400 K. For the energetic component, our models indicate that the column abundance that can be attributed to sputtering under constant southward interplanetary magnetic field conditions is at least a factor of five less than the rate dictated by the measurements. Although highly uncertain, this result suggests that another energetic process, such as the rapid dissociation of exospheric MgO, may be the main source of the distant neutral component. If meteoroid and micrometeoroid impacts eject mainly molecules, the total amount of magnesium at altitudes exceeding similar to 100 km is found to be consistent with predictions by impact vaporization models for molecule lifetimes of no more than two minutes. Though a sharp increase in emission observed near the dawn terminator region can be reproduced if a single meteoroid enhanced the impact vapor at equatorial dawn, it is much more likely that observations in this region, which probe heights increasingly near the surface, indicate a reservoir of volatile Mg being acted upon by lower-energy source processes. (C) 2011 Elsevier Ltd. All rights reserved.

Journal Title

Planetary and Space Science

Volume

59

Issue/Number

15

Publication Date

1-1-2011

Document Type

Article

Language

English

First Page

1992

Last Page

2003

WOS Identifier

WOS:000298722800016

ISSN

0032-0633

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