Modeling MESSENGER observations of calcium in Mercury's exosphere

被引:28
作者
Burger, Matthew H. [1 ,2 ]
Killen, Rosemary M. [1 ]
McClintock, William E. [3 ]
Vervack, Ronald J., Jr. [4 ]
Merkel, Aimee W. [3 ]
Sprague, Ann L. [5 ]
Sarantos, Menelaos [6 ,7 ]
机构
[1] NASA, Planetary Magnetospheres Lab, Solar Syst Explorat Div, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[2] Morgan State Univ, Baltimore, MD 21239 USA
[3] Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80309 USA
[4] Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA
[5] Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA
[6] NASA, Heliophys Sci Div, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[7] Univ Maryland Baltimore Cty, Goddard Planetary Heliophys Inst, Catonsville, MD USA
关键词
SODIUM; ATMOSPHERE; MARINER-10; DISCOVERY; MAGNESIUM; TRANSIT; SURFACE; NA;
D O I
10.1029/2012JE004158
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MESSENGER spacecraft has made the first high-spatial-resolution observations of exospheric calcium at Mercury. We use a Monte Carlo model of the exosphere to track the trajectories of calcium atoms ejected from the surface until they are photoionized, escape from the system, or stick to the surface. This model permits an exploration of exospheric source processes and interactions among neutral atoms, solar radiation, and the planetary surface. The MASCS data have suggested that a persistent, high-energy source of calcium that was enhanced in the dawn, equatorial region of Mercury was active during MESSENGER's three flybys of Mercury and during the first seven orbits for which MASCS obtained data. The total Ca source rate from the surface varied between 1.2 x 10(23) and 2.6 x 10(23) Ca atoms s(-1), if its temperature was 50,000 K. The origin of this high-energy, asymmetric source is unknown, although from this limited data set it does not appear to be consistent with micrometeoroid impact vaporization, ion sputtering, electron-stimulated desorption, or vaporization at dawn of material trapped on the cold nightside.
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页数:15
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