SPECTRAL PROPERTIES OF AN UNUSUAL IMPACT MELT FLOW ON MERCURY: INTEGRATING COLOR IMAGERY WITH SPECTRAL DATA ACQUIRED BY MASCS ON MESSENGER

Color images collected by the Mercury Dual Imaging System (MDIS) on MESSENGER have revealed diverse compositional provinces across the surface of the planet. The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) enables a detailed characterization of these units by providing high-spectral-resolution measurements from ultraviolet to near-infrared wavelengths. Observed spectral differences between units reflect both compositional and maturity effects. Since MESSENGER entered orbit on March 18, 2011, well over half a million spectra have been collected of the surface of Mercury. An unusual feature observed by both MDIS and MASCS is a spectrally distinct flow, extending from a 12-km-diameter crater located to the northeast of Beethoven basin, at approximately 9° S and 255° E. The dark flow, first evident in Mariner 10 images, is about 12 km wide and extends approximately 20 km to the southeast of the unnamed crater. MDIS color images reveal that in addition to the overall dark albedo, the flow has a relatively shallower (bluer) spectral slope with increasing wavelength than the surrounding terrain. MASCS spectra of the flow suggest that this slope difference extends to infrared wavelengths and that the fresh ejecta from this crater exhibit a substantially higher reflectance but a similar spectral slope to the flow. We integrate eight-color MDIS images of the dark flow and surrounding regions with MASCS spectra to assess the extent of the material excavated by the unnamed crater and to compare its spectral properties to material of similar maturity in the region. Because of the distinctive albedo and color contrast at and around this feature, these observations also provide a key tie point for integration of MDIS color and MASCS data on a global scale. Such combined spectral studies are critical to understanding surface composition and space weathering effects on Mercury, as they capitalize on the higher spatial resolution and geologic context provided by MDIS and the high spectral resolution and broader spectral range provided by MASCS.