Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p21a1190d&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P21A-1190
Other
[5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties
Scientific paper
The MEcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft obtained photometric observations of Mercury during three flybys (14 January 2008, 6 October 2008, 29 September 2009) using both the Mercury Dual Imaging System (MDIS) and the Mercury Atmospheric and Surface Composition Spectrometer (MASCS). The MDIS measurements include disk-integrated phase-curve observations taken in 11 narrow-band filters ranging from 430 to 1010 nm. The MDIS measurements also include disk-resolved photometric observations taken during the first flyby of a 200-km by 400-km region (centered on 1.7°S, 123.5°E, and spanning 5.5° of latitude and 10° of longitude) over a phase-angle range between 51° and 120°. The MASCS measurements include disk-integrated phase-curve observations taken from 300 to 1450 nm at a spectral resolution of 2.5 nm. During the third flyby, targeted type regions were observed at multiple viewing geometries, providing disk-resolved photometric measurements at high spectral resolution. Comparisons with ground-based observations show that the phase behavior determined by analysis of the MDIS and MASCS observations is consistent with previous studies. Reflectance measurements from the first two flybys show no definitive absorption features and a distinctive steep, or “red,” slope with increasing wavelength common to space-weathered rocky surfaces. The MDIS spectra show evidence of phase reddening (increased spectral slope with increasing phase angle), similar to that observed on the Moon. The derived photometric properties indicate a more compact, less porous regolith that is smoother on meter scales than regolith on the Moon or S-type asteroids. Although Mercury is darker than the average lunar nearside, the calculated geometric albedo (reflectance at zero phase) is higher for Mercury than the Moon, implying a greater opposition-surge magnitude. The geometric albedo, coupled with the lower reflectance of immature (younger) units on Mercury compared with immature units on the Moon, indicates more heterogeneous grains (marked by variations in composition and structure to produce more scattering centers) within Mercury’s regolith, implying differences in the maturation processes and products between Mercury and the Moon. Ion and micrometeoroid bombardment are the dominant maturation processes on lunar and asteroid surfaces, but each matures the surface at different rates and affects regolith grain characteristics (size, shape, and composition) in different manners. Photometric analysis provides insight into regolith grain properties on Mercury and can help resolve signatures of distinct maturation processes.
Blewett Dave T.
Denevi Brett Wilcox
Domingue Donovan
Holsclaw Gregory M.
Izenberg Noam R.
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