Presentation #302.05 in the session “Moon and Mercury 1”.
Carbon, as graphite, emerged from analyses of Mercury MESSENGER spectrophotometry and theoretical modeling as a possible source for the darkening component in Mercury’s Low Reflectance Material (LRM), pervasive across the equatorial surface. The presence of a 600-nm absorption in the Mercury Dual Imaging System (MDIS) photometry suggested graphite in amounts consistent with the results from MESSENGER’s elemental experiments for the presence of C was proposed as the most likely darkening component in LRM. Two general theories about the origin of the carbon have been proposed. In one scenario, graphite would be the only buoyant phase in an early magma ocean, and any primary flotation crust would have retained C in the form of graphite. Carbon from cometary sources has also been proposed to be the darkening material. Alternatively, nanophase and microphase iron (rather than C), produced by impacts into Mercury’s crust before and during the late heavy bombardment, could darken the LRM. Graphitized carbon has distinctive far-UV spectral reflectance features that change with the level of graphitization. We are re-analyzing Mariner 10 Extreme Ultraviolet (EUV) airglow spectrometer data in a search for this distinctive UV signature of graphitized carbon across large areas of Mercury’s surface. The spectrometer observed broad swaths of Mercury’s surface during Fly-bys 1 (29 Mar 1974) and 3 (16 Mar 1975). The same side of the planet was always observed during the mission. One observation set includes counts through 10 filters at the wavelengths 304, 430, 580, 740, 869, 1048, 1216, 1304, 1480, 1659 Å, each having 20 Å passbands. A slit cutting across the disk in one direction was stepped across the visible portion of the planet’s disk. We have uncovered ~880 individual sets of photometry covering all or part of Mercury’s surface. For each observation, we are projecting the slits onto the 8-color multispectral 17-band MESSENGER high-resolution (~665 m/pixel) global mosaic of Mercury, to view the surface area covered by the slit during the observation and derive the corresponding visible photometry. For each observation, we also expect to produce corrected I/F values in each filter.