Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53c1528e&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P53C-1528
Other
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5494] Planetary Sciences: Solid Surface Planets / Instruments And Techniques, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Many martian craters possess fluidized ejecta morphologies and topography indicative of surface flow. These morphologies are usually thought to be the product of surface volatiles. However, two other viable processes have also been proposed: strong atmospheric winds that entrain ejecta and deposition by a simple granular flow. A combination of these models may also explain the observed morphologies, and each model possesses specific implications for volatile content and atmospheric properties of Mars. Regardless of the mechanics involved, it is generally agreed that excavated ejecta at these craters must have flowed across the surface. Several studies have modeled the fluidized ejecta emplacement process as a continuum surface flow, but to this point none of these models can match all the aspects of the observed ejecta. A new, large-scale experimental apparatus has been constructed to investigate the mechanics of ballistic emplacement of the continuous and denser components of the ejecta and the subsequent surface flow that could generate fluidized morphologies. The ejecta emplacement simulator, or EESim, consists of an ejecta launcher plate, a series of strong springs, and a target box. It is capable of launching a 0.9m high, 2.0m wide sheet of ejecta that can be between 1 and 8cm thick. The simulated curtains have velocity distributions and structures that are nearly identical to ejecta curtains generated by impacts. At its maximum speed of 10m/s, the EESim curtain is approximately equivalent to that generated by a 25m-diameter crater, far larger than craters produced during laboratory experiments. The simulated crater size can be changed by varying the launch velocity. The interaction of different portions of an ejecta curtain with the target surface can be explored by changing the mass of the debris to be launched. Preliminary tests using the EESim are currently being undertaken. These tests investigate the detailed physics of ejecta emplacement that influence run-out, morphology and topography. The results will establish whether or not the susceptibility of a surface to erosion has a significant influence on the ejecta deposition and subsequent flow mechanics and are likely to provide quantitative measurements for the onset conditions for surface flow.
Barnouin Olivier S.
Ernst Carolyn M.
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