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Ejecta–megaregolith accumulation on planetesimals and large asteroids
Author(s) -
WARREN Paul H.
Publication year - 2011
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2010.01138.x
Subject(s) - impact crater , ejecta , planetesimal , asteroid , radius , regolith , geology , porosity , thermal conductivity , mineralogy , astrobiology , solar system , physics , astrophysics , thermodynamics , geotechnical engineering , computer security , supernova , computer science
– 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 lowers thermal conductivity by a factor of 10. I have modeled global average ejecta accumulation as a function of the largest impact size, with no explicit modeling of time. In conjunction with an assumed cratering size‐distribution exponent b , the largest crater constrains the sizes of all other craters that significantly contribute to a megaregolith. The largest impactor mass ratio is a major fraction of the catastrophic‐disruption mass ratio, and in general the largest crater’s diameter is close to the target’s diameter. Total accumulation is roughly 1–5% of (and proportional to) the target’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 (typical) largest crater size. For b ∼ 2, the single largest crater typically contributes close to 50% of the total of new (nonrecycled) ejecta. Megaregolith can be destroyed by sintering, a process whose pressure sensitivity makes it effective at lower temperature on larger bodies. Planetesimals ∼100 km in diameter may be surprisingly well suited (about as well suited as bodies two to three times larger in diameter) for attaining temperatures conducive to widespread melting. A water‐rich composition may be a significant disadvantage in terms of planetesimal heating, as the shallow interior may be densified by aqueous metamorphism, and will have a low sintering temperature.