Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p41f..06b&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P41F-06
Other
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [5460] Planetary Sciences: Solid Surface Planets / Physical Properties Of Materials, [6235] Planetary Sciences: Solar System Objects / Mercury
Scientific paper
Topographic data acquired by the Mercury Laser Altimeter (MLA) and images from the Mercury Dual Imaging System (MDIS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft are used to investigate the geomorphology of several fresh impact craters on Mercury. This analysis expands on previous efforts with Mariner 10 data to understand how craters on Mercury compare to similarly sized craters on other planets and moons. In particular, comparisons to craters on Mars, which has a surface gravitational acceleration nearly identical to that of Mercury, yield insights into the effects of surface properties, especially target strength, on crater morphology. Establishing the geomorphology of typical fresh craters on Mercury also will provide a baseline for assessing the modification of less well-preserved craters by volcanism, tectonics, and subsequent impacts. Hokusai crater, whose rays envelop much of the planet, is one of the freshest on the surface of Mercury. High-resolution MDIS images (~36 m/pixel) reveal few superposed craters on this 100-km-diameter crater, and several MLA profiles that pass through its center indicate that it is ~2 km deep from rim crest to crater floor, making it extremely deep for a crater of its diameter on Mercury. Impact melt fills the interior of Hokusai this crater, embaying a semi-circular central peak structure. The melt possesses small cracks that are likely due to cooling. Small variations in brightness seen in the melt deposit seem to be associated with small undulations in the topography as measured by MLA, possibly due to the underlying terrain. Some of the impact melt lies in local depressions within the terraces of the crater wall, and some in patches located throughout the crater ejecta. Hokusai crater also possesses intriguing topographic features in its near-rim ejecta field. The MLA data indicate that the thickness of ejecta beyond the crater rim is not well modeled by a power-law function of radial distance r of the form (r/R)-3, where R is the crater rim radius, as is often used to describe ejecta emplaced ballistically. A moat separates the rim from much of the continuous ejecta, which sometimes ends in a terminal rampart up to 500-m in height, somewhat reminiscent of single-layered ejecta facies seen on Mars. Equivalent-sized craters on the Moon do not possess such features. The run-out distance (r <2 R) of the continuous Hokusai ejecta delineated by these ramparts is far smaller than for equivalent sized craters on Mars (r >2 R). The origin of Hokusai's ramparts is currently not understood, but they could be a result of granular flow processes that likely follow the initial ballistic deposition of ejecta. The vast amounts of melt present at this impact crater could also have influenced ejecta emplacement. Investigations of other fresh craters on Mercury will provide additional clues as to how observed ejecta facies are related to surface properties and the presence of impact melt.
Barnouin Olivier S.
Chabot Nancy Lynne
Ernst Carolyn M.
Murchie Scott L.
Neumann Gregory A.
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