Title

Monte Carlo modeling of sodium in Mercury's exosphere during the first two MESSENGER flybys

Authors

Authors

M. H. Burger; R. M. Killen; R. J. Vervack; E. T. Bradley; W. E. McClintock; M. Sarantos; M. Benna;N. Mouawad

Comments

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Abbreviated Journal Title

Icarus

Keywords

Mercury, Atmosphere; Mercury, Surface; Atmospheres, Structure; Magnetospheres; PHOTON-STIMULATED DESORPTION; SOLAR-WIND; ATMOSPHERE; SURFACE; POTASSIUM; LUNAR; RADIATION; IMPACT; NA; MARINER-10; Astronomy & Astrophysics

Abstract

We present a Monte Carlo model of the distribution of neutral sodium in Mercury's exosphere and tail using data from the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft during the first two flybys of the planet in January and September 2008 We show that the dominant source mechanism for ejecting sodium from the surface is photon-stimulated desorption (PSD) and that the desorption rate is limited by the diffusion late of sodium from the interior of grains in the regolith to the topmost few monolayers where PSD is effective In the absence of ion precipitation, we find that the sodium source rate is limited to similar to 10(6)-10(7) cm(-2) s(-1), depending on the sticking efficiency of exospheric sodium that returns to the surface The diffusion rate must be at least a factor of 5 higher in regions of ion precipitation to explain the MASCS observations during the second MESSENGER flyby We estimate that impact vaporization of micrometeoroids may provide up to 15% of the total sodium source rate in the regions observed Although sputtering by precipitating ions was found not to be a significant source of sodium during the MESSENGER flybys, ion precipitation is responsible for increasing the source rate at high latitudes through ion-enhanced diffusion (C) 2010 Elsevier Inc. All rights reserved

Journal Title

Icarus

Volume

209

Issue/Number

1

Publication Date

1-1-2010

Document Type

Article

Language

English

First Page

63

Last Page

74

WOS Identifier

WOS:000281687800008

ISSN

0019-1035

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