Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.0206m&link_type=abstract
American Astronomical Society, DPS meeting #40, #2.06; Bulletin of the American Astronomical Society, Vol. 40, p.388
Astronomy and Astrophysics
Astrophysics
Scientific paper
The detailed images of comet Tempel 1 returned by the Deep Impact spacecraft revealed several smooth, uncratered plateaus terminated by steep scarps. The most prominent smooth terrain is longitudinally striated and slopes monotonically downward from an apparent source crater with an average gradient of about 3°. We propose that these smooth areas are gas-fluidized landslides. They resemble terrestrial catastrophic rock avalanches such as the Alaskan Sherman Glacier landslide of 1964. However, in the case of Tempel 1, we suggest that the fluidizing agent is gas that ejected a mass of material during past outburst events. This fine-grained material trapped a quantity of gas and, as the gas slowly diffused out of the moving mass, moved downslope as a mobile debris flow, similar in concept to terrestrial mudflows that are fluidized by water (the pressure in both obeys precisely the same equation, but this differs from a terrestrial pyroclastic flow). The mass of material that remains on the surface, comprising about 1010 kg of fine particulates in the best-imaged example, flowed away from its source down the local gravitational gradient. . Due to their high density and thus relatively high viscosity, these flows traveled in a laminar regime and halted abruptly as the fluidizing gas escaped, leaving a steep terminal scarp. Nevertheless, the flow viscosity was not high enough to seriously impede its motion, which was nearly frictionless during most of its travel. Several methods of estimating the flow viscosity agree in placing it between 30 and 100 Pa-sec. The time scale for emplacement was a few hours and the maximum velocity about 0.3 m/sec.
Belton Michael J. S.
Melosh Henry Jay
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