Title

Limits To Mercurys Magnesium Exosphere From Messenger Second Flyby Observations

Keywords

Atmospheric structure; Mercury; Mercury atmosphere; Mercury magnetosphere; Mercury surface; MESSENGER

Abstract

The discovery measurements of Mercurys 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 ∼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. © 2011 Elsevier Ltd. All rights reserved.

Publication Date

12-1-2011

Publication Title

Planetary and Space Science

Volume

59

Issue

15

Number of Pages

1992-2003

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1016/j.pss.2011.05.002

Socpus ID

82455199288 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/82455199288

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