Other
Scientific paper
Oct 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.3938w&link_type=abstract
American Astronomical Society, DPS meeting #42, #39.38
Other
Scientific paper
Megaregolith accumulation can have important thermal consequences for bodies that lose heat by conduction, as vacuous porosity of the kind observed in the lunar megaregolith can lower conductivity by a factor of 10 or more. I have modeled global average ejecta accumulation as a function of the largest impact crater size, with no explicit modeling of time. In conjunction with an assumed cratering size-distribution exponent b, the largest crater implicitly constrains the sizes of all other craters significant to a final megaregolith. The largest-impactor mass ratio is probably a major fraction of the catastrophic-disruption mass ratio, and in general the largest crater's diameter is close to the target body's d. Total ejecta accumulation is then roughly proportional to d, and with conservative parameter assumptions (e.g., b 2) will be 1-5% of the body's radius. Global accumulations estimated by this approach are higher than in the classic Housen et al. (1979) study by a factor of roughly 10. This revision is caused mainly by higher largest crater size, caused in turn by higher estimated catastrophic-disruption mass ratio. For modeling of thermal implications, significant stochastic variations probably arise from two effects: concentration of ejecta mass into a relative few large fragments; and uneven distribution, especially on small bodies. Megaregolith destruction by sintering is pressure sensitive and thus effective at generally far lower temperature on larger (>> 100 km) bodies. Planetesimals 100 km in d may be surprisingly well-suited (about as well-suited as bodies 2-3 times larger) for attaining temperatures conducive to widespread melting.
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