Evidence Connecting Mercury's Magnesium Exosphere to Its Magnesium‐Rich Surface Terrane. Issue 14 (15th July 2018)

• Record Type: Journal Article
• Authors: Merkel, Aimee W.; Vervack, Ronald J.; Killen, Rosemary M.; Cassidy, Timothy A.; McClintock, William E.; Nittler, Larry R.; Burger, Matthew H.
• Is Part Of: Geophysical research letters. Volume 45:Issue 14(2018)
• Page Start: 6790
• Page End: 6797
• Publication Date: 2018-07-15
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2018GL078407
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Mercury is surrounded by a tenuous, collisionless exosphere where the surface of the planet is directly exposed to the space environment. As a consequence, impacts and space weathering processes are expected to eject atoms and molecules from the surface into the exosphere, implying a direct link between the exospheric composition and the planet's regolith material. However, observational evidence demonstrating this link has been elusive. Here we report that exospheric magnesium, a species recently discovered and systematically measured by the Mercury Surface, Space ENvironment, GEochemistry, and Ranging mission, is enhanced when observed over a portion of the planet's surface regolith rich in magnesium. These observations confirm a direct link between Mercury's magnesium exosphere and the underlying crustal surface composition, providing strong evidence supporting theoretical arguments that impact vaporization can directly supply material to the exosphere from the regolith of a rocky, airless body. Plain Language Summary: Understanding the physical processes that release atoms and molecules from Mercury's surface into its exosphere (highly tenuous atmosphere) has been a major challenge because it is difficult to observe Mercury from the ground or Earth's orbit. From its orbit around the planet, the Mercury Surface, Space ENvironment, GEochemistry, and Ranging mission provided the first detailed view of Mercury's surface composition and its space environment. Because Mercury is an airless body, its exosphere must constantly be replenished, and it has been assumed that it is directly sourced from the planet's surface. However, a direct observation connecting the surface and the exosphere was not possible until the Mercury Surface, Space ENvironment, GEochemistry, and Ranging mission. Using observations of exospheric magnesium (Mg) and colocating them with a Mg‐rich region of Mercury's surface shows for the first time that such a link exists. The results suggest that incoming micrometeoroid particles (dust) can access the surface crustal composition directly and release Mg atoms into the surrounding environment. Our work will inform future exospheric models and provide insights into airless body processes for both other solar system objects and Mercury‐like exoplanets. Key Points: We present the first observational evidence of a direct connection between Mercury's exosphere and the surface crustal composition A 1:1 correlation was found between the production of magnesium and the regional distribution of magnesium on Mercury's surface Our results support theoretical arguments that micrometeoroid impact vaporization can directly source material from the regolith of rocky, airless bodies