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Constraints on Mercury's Na Exosphere: Combined MESSENGER and Ground-Based DataWe have used observations of sodium emission obtained with the McMath-Pierce solar telescope and MESSENGER's Mercury Atmospheric and Surface Composition Spectrometer (MASCS) to constrain models of Mercury's sodium exosphere, The distribution of sodium in Mercury's exosphere during the period January 12-15. 2008. was mapped using the McMath-Pierce solar telescope with the 5" X 5" image slicer to observe the D-line emission. On January 14, 2008, the Ultraviolet and Visible Spectrometer (UVVS) channel on MASCS sampled the sodium in Mercury's anti-sunward tail region. We find that the bound exosphere has an equivalent temperature of 900-1200 K, and that this temperature can be achieved if the sodium is ejected either by photon-stimulated desorption (PSD) with a 1200 K Maxwellian velocity distribution, or by thermal accommodation of a hotter source. We were not able to discriminate between the two assumed velocity distributions of the ejected particles for the PSD. but the velocity distributions require different values of the thermal accommodation coefficient and result in different upper limits on impact vaporization, We were able to place a strong constraint on the impact vaporization rate that results in the release of neutral Na atoms with an upper limit of 2.1 x 10(exp 6) sq cm/s, The variability of the week-long ground-based observations can be explained by variations in the sources, including both PSD and ion-enhanced PSD, as well as possible temporal enhancements in meteoroid vaporization. Knowledge of both dayside and anti-sunward tail morphologies and radiances are necessary to correctly deduce the exospheric source rates, processes, velocity distribution, and surface interaction.
Document ID
20110013529
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Mouawad, Nelly
(Maryland Univ. College Park, MD, United States)
Burger, Matthew H.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Killen, Rosemary M.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Potter, Andrew E.
(National Solar Observatory Tucson, AZ, United States)
McClintock, William E.
(Colorado Univ. Boulder, CO, United States)
Vervack, Ronald J., Jr.
(Johns Hopkins Univ. Laurel, MD, United States)
Bradley, E. Todd
(University of Central Florida Orlando, FL, United States)
Benna, Mehdi
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Naidu, Shantanu
(Maryland Univ. College Park, MD, United States)
Date Acquired
August 25, 2013
Publication Date
November 4, 2010
Publication Information
Publication: Icarus
Volume: 211
Issue: 1
Subject Category
Lunar And Planetary Science And Exploration
Report/Patent Number
GSFC.JA.4590.2011
Funding Number(s)
CONTRACT_GRANT: NNX07AR63G
CONTRACT_GRANT: NNX08AP65G
CONTRACT_GRANT: NNX08AI31G
CONTRACT_GRANT: NNX07AR78G
CONTRACT_GRANT: NNG05GF53G
Distribution Limits
Public
Copyright
Other

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