P53A-2093
Analysis of Ultraviolet Reflectance Spectra of Mercury’s Southern Hemisphere
Friday, 18 December 2015
Poster Hall (Moscone South)
Noam Izenberg1, Rachel E Maxwell2, Gregory M Holsclaw3, Rachel L Klima4, Sean C Solomon5 and William E. McClintock3, (1)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, (2)Purdue University, Earth, Atmospheric, and Planetary Science Department, West Lafeyette, IN, United States, (3)Univ Colorado, Boulder, CO, United States, (4)JHU Applied Physics Lab, Laurel, MD, United States, (5)Columbia University of New York, Palisades, NY, United States
Abstract:
The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft conducted orbital observations of Mercury’s surface from 29 March 2011 to the end of the mission on 30 April 2015. Observing the daylit surface nearly every orbit, the Visible and Infrared Spectrograph (VIRS) component of MASCS obtained near-global coverage of reflectance at ultraviolet through near-infrared wavelengths (300 though 1450 nm). Additionally, the Ultraviolet and Visible Spectrometer (UVVS) component of MASCS acquired several thousand surface spectra over the wavelength range 220 to 300 nm. UVVS observations were conducted one at a time, targeting single ~25 km2 areas on the surface. A series of acquisition campaigns obtained UVVS data in target grids of one observation every 200 km across Mercury’s southern hemisphere, with the highest-quality data obtained in the last year of the mission. Each UVVS grid observation was accompanied by contemporaneous VIRS observations with the same viewing geometry and instrument conditions. Joint analyses of ultraviolet reflectance, reflectance ratios, and absorption bands derived from over 1900 UVVS observations co-sited with those from VIRS yield several notable contrasts. Across the southern hemisphere, regions of low-reflectance material (LRM), identified through color imaging by the Mercury Dual Imaging System (MDIS) to be low in overall reflectance and low in visible to near infrared spectral slope, also have low spectral slope at short VIRS wavelengths (310 nm / 390 nm), but higher slope in UVVS wavelengths (220 nm / 290 nm). A VIRS-based spectral band derivation, with continuum slope between 480 nm and 830 nm and center wavelength at 630 nm, similar to one derived for MDIS and interpreted to be potentially indicative of the presence of sulfides or carbon, shows moderate to low values for LRM, and higher values for smooth plains. A UVVS-based band, with continuum slope between 220 nm and 290 nm and center wavelength at 260 nm, shows greater band depths in and near LRM regions. Ongoing analysis seeks to interpret whether the UVVS wavelengths can aid compositional distinctions such as between darkening agents such as nanophase iron and carbon, which have different ultraviolet signatures.
