Mercury's exosphere: A possible source for Na |
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| Institution: | 1. Lunar and Planetary Laboratory, University of Arizona, 1629 E, University Blvd, Tucson, AZ 85721-0092, USA;2. Binary Systems P/L, 98 William Street, Brookvale NSW 2100, Australia;1. INAF Osservatorio Astronomico Padova, Padova, Italy;2. Service d'' Aéronomie, Université de Paris Pierre et Marie Curie, Paris, France;1. University of Houston, Dept. of Earth and Atmospheric Sciences, 312 Science & Research 1, Houston, TX 77204, United States;2. NASA-JSC, 2101 NASA Parkway, MS KR, Houston, TX 77058, USA;3. University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 ESB, Edmonton, Alberta, Canada T6G 2E3;4. Dept. of Earth, Ocean and Atmospheric Science and National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA;5. Jacobs Technology, E.S.C.G., Mail Code JE23, 2224 Bay Area Blvd, Houston, TX 77058, USA;1. Jet Propulsion Lab., MS 268–600, Pasadena, CA 91109, U.S.A;2. JILA, CB 440, Univ. of Colorado, Boulder, CO 80309, U.S.A.;3. Dept. of Physics, Univ. of California, Santa Barbara, CA 93106, U.S.A.;4. Aerospace Engineering Sciences Dept., CB 429, Univ. of Colorado, Boulder, CO 80309, U.S.A.;5. Jet Propulsion Lab., MS 301-165. Pasadena, CA 91109, U.S.A. |
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| Abstract: | Many ground-based observations of Na in Mercury's surface-bounded exosphere have been made and continued to be made in an effort to understand the sources, sinks, and distribution of Na around Mercury. These time consuming and costly efforts are made to better understand the physical processes on and around Mercury. A big step would be to discover an actual source of the Na from Mercury's crust because it is already known that meteorites and comets provide Na to the exosphere through impact. We provide ground-based CCD imagery obtained with small ground-based telescopes that show bright albedo features at locations coincident with enhanced Na emissions in Mercury's exosphere. We suggest these locations are sources for Na. We also provide a mechanism to test this hypothesis using in situ observations by instruments on the MESSENGER spacecraft during the three fly bys of Mercury that will occur in 2008 and 2009, and during the orbital mission which begins in 2011. It is necessary to prove that Na is delivered to the exosphere from one or more crustal source regions before exospheric Na can be used as a measure of the volatile content of Mercury used to infer formation and evolution from the primitive solar nebula. The same applies to other elements such as K which is known to be in Mercury's exosphere and S which is postulated to be present. We expound on the impact that the discovery of one or more source regions from Mercury's crust would have on our ability to discern between the three leading models of Mercury's formation and crustal evolution. |
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