Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.u12a..06m&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #U12A-06
Physics
0328 Exosphere, 5405 Atmospheres (0343, 1060), 6235 Mercury
Scientific paper
Mercury's surface-bounded exosphere is the interface between the planet's surface and the external stimuli that interact with it. The exosphere's composition and structure are controlled by surface, magnetosphere, solar wind, and solar irradiance processes. Prior to the MESSENGER mission the exosphere was known to contain H, He, and O from Mariner 10 observations, as well as Na, K, and Ca that were discovered during ground-based observations. Na in particular has been extensively studied since its discovery in 1985. When species are liberated from the surface with sufficient energy they can be accelerated by solar radiation pressure to form a tail that extends in the direction opposite to that of the Sun. Observations of Mercury's neutral Na tail were first reported in 2002. During MESSENGER's initial flyby of Mercury, which occurred on January 14, 2008, the Ultraviolet and Visible Spectrometer (UVVS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) made the first observations of the Na tail from space beginning at an altitude of 24,500 km behind Mercury's nightside surface and covering a region of space approximately three planet diameters tall and centered on the Sun-Mercury line. The spatial distribution of Na was seen to be asymmetric, with enhanced density occurring in the northern hemisphere. UVVS observations of Ca, which were made as the spacecraft traversed the nightside exosphere, exhibited enhanced emission toward the dawn terminator. These results suggest that the relatively high-energy source processes that give rise to species observed in the tail were localized near the northern and morning hemispheres during the flyby. On the dayside of the planet, UVVS observations of neutral H revealed an altitude distribution consistent with the "warm" (T ~ 420 K) exospheric component seen by Mariner 10. During the second flyby of Mercury, which will occur on October 6, 2008, the UVVS will be configured to measure Na, Ca, and Mg in the tail and near-planet nightside regions. On the dayside, high time-cadence measurements will be used to study the detailed altitude distribution of H at low altitudes and both H and Na at altitudes above 800 km. Because Mercury's true anomaly during the second flyby (294°) will be close to that of the first flyby (285°), differences in the composition of the tail are more likely to be the result of changes in solar wind and magnetosphere conditions than of seasonal effects.
Bradley Eric Todd
Izenberg Noam R.
Killen Rosemary Margaret
Kochte M. C.
Lankton Mark R.
No associations
LandOfFree
Observations of Mercury's Exosphere With the Mercury Atmospheric and Surface Composition Spectrometer During the Second MESSENGER Flyby does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Observations of Mercury's Exosphere With the Mercury Atmospheric and Surface Composition Spectrometer During the Second MESSENGER Flyby, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Observations of Mercury's Exosphere With the Mercury Atmospheric and Surface Composition Spectrometer During the Second MESSENGER Flyby will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1240400