Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p23d..04e&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P23D-04
Physics
[5410] Planetary Sciences: Solid Surface Planets / Composition, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6235] Planetary Sciences: Solar System Objects / Mercury
Scientific paper
MESSENGER’s Mercury Dual Imaging System (MDIS), consisting of a monochrome, narrow-angle camera and an 11-band (430-1020 nm), wide-angle camera, imaged approximately 80% of the surface of Mercury during its first two flybys. These images confirm that the surface of Mercury exhibits subtle color variations, which are associated with changes in the steepness of the spectral slope over the MDIS wavelength range. Although the first-order color variations are due to maturity effects, some color variations can be attributed to compositional differences. In many areas, impact craters are associated with material that is spectrally distinct from the surrounding surface. These deposits can be located on the crater floor, rim, wall, or central peak, or in the ejecta blanket, and represent material that originally resided at depth and was subsequently excavated by impacts. The resulting craters make it possible to investigate the stratigraphy of Mercury’s upper crust. Studies of laboratory, terrestrial, and lunar craters provide a means to estimate, or at least bound, the depth of origin of the spectrally distinct ejecta and central peak structures. Craters of varying size in the same region can be used to constrain the vertical and horizontal extent of subsurface materials. Excavated red material (RM), with comparatively steep or “red” spectral slope, and low-reflectance material (LRM) stand out prominently from the surrounding terrain in enhanced-color images, as they are spectral end-members in Mercury’s compositional continuum. Examples of RM were found to be spectrally similar to the relatively red, high-reflectance plains (HRP), suggesting that they may represent deposits of HRP-like material that were subsequently covered by thinner (~1 km thick) intermediate plains. In one area, craters with diameters ranging from 30 km to 130 km have excavated and incorporated RM into their rims, suggesting that the underlying RM layer may be several kilometers thick. LRM deposits are often associated with ejecta from large craters and basins, but not all large craters and basins have excavated LRM, indicating a heterogeneous distribution across the planet. The presence of LRM in the central peaks of some large craters indicates that this material is at least locally present at a depth of several kilometers. Some RM and LRM were excavated by pre-Tolstojan basins, indicating a relatively old age (> 4.0 Ga). The examination of several small areas on Mercury reveals the complex nature of the local stratigraphy and supports sequential buildup of most of the upper ~5 km of crust by volcanic flows with compositions spanning the range of material now visible on the surface, distributed heterogeneously across the planet. MESSENGER’s third flyby of Mercury on 29 September 2009 collected new high-resolution color and monochrome images of specific targets. These images allow additional in-detail examinations of local areas, improving our understanding of Mercury’s crustal stratigraphy.
Barnouin-Jha Olivier Serge
Blewett Dave T.
Denevi Brett Wilcox
Ernst Carolyn M.
Head James W.
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