Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p52a..04m&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P52A-04
Astronomy and Astrophysics
Astrophysics
5470 Surface Materials And Properties, 6023 Comets: Dust Tails And Trails (6210), 6055 Surfaces, 6063 Volcanism (5480, 8450), 6210 Comets (6023)
Scientific paper
The Deep Impact mission discovered several smooth terrains and repetitive outbursts on comet 9P/Tempel 1 suggestive of cryo-volcanic activity in its interior. We present new measurements of the extent of the smooth terrains, the slopes along their centerlines, and the areas of their likely source regions and vents. Our analysis of these features indicates that they may be only a few orbits old and the result of an ongoing process. Based on the source locations of repetitive outbursts, we propose that the smooth terrains originate from different regimes of fluidization and gas transport in a weakly bound particulate mixture of ice and dust above an amorphous to crystalline water ice phase transformation boundary where CO and/or CO2 is released. The stresses due to gas pressure extrude, at low velocity, fluidized and dilated, gas-laden cometary material onto the surface leading to downhill flow and subsequent collapse of the evacuated cavity. The most prominent smooth terrain is longitudinally striated and slopes monotonically downward from an apparent source crater with an average gradient of about 3 deg. It resembles terrestrial catastrophic rock avalanches such as the Alaskan Sherman Glacier landslide of 1964. However, in the case of Tempel 1 the fluidizing agent is CO or CO2 gas. The gas-charged material erupted onto the surface 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 comprises about 10E10 kg of fine particulates in the best-imaged example. 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
Melosh Henry Jay
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