A cold‐pole enhancement in Mercury's sodium exosphere. Issue 21 (8th November 2016)

• Record Type: Journal Article
• Authors: Cassidy, Timothy A.; McClintock, William E.; Killen, Rosemary M.; Sarantos, Menelaos; Merkel, Aimee W.; Vervack, Ronald J.; Burger, Matthew H.
• Is Part Of: Geophysical research letters. Volume 43:Issue 21(2016)
• Page Start: 11, 121
• Page End: 11, 128
• Publication Date: 2016-11-08
• Subjects: Mercury -- exosphere -- dynamics; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2016GL071071
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The ultraviolet and visible spectrometer component of the Mercury Atmospheric and Surface Composition Spectrometer on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft characterized the local‐time distribution of the sodium exosphere over the course of its orbital mission. The observations show that the sodium exosphere is enhanced above Mercury's cold‐pole longitudes. Based on previously published sodium exosphere models, we infer that these regions act as night side surface reservoirs, temporary sinks to the exosphere that collect sodium atoms transported antisunward. The reservoirs are revealed as exospheric enhancements when they are exposed to sunlight. As in the models the reservoir is depleted as the cold poles rotate from dawn to dusk, but unlike the models the depletion is only partial. The persistence of the reservoir means that it could, over the course of geologically long periods of time, contribute to an increase in the bulk concentration of sodium near the cold‐pole longitudes. Key Points: MESSENGER observed a sodium exosphere enhancement above Mercury's cold‐pole longitudes The cold poles act as temporary sinks to the exosphere that are revealed as exospheric enhancements when exposed to sunlight These reservoirs could help explain the high sodium concentration seen in Mercury's high‐latitude northern hemisphere