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The small‐comet hypothesis: An upper limit to the current impact rate on the moon
Author(s) -
Grier Jennifer A.,
McEwen Alfred S.
Publication year - 1997
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/97gl03225
Subject(s) - impact crater , comet , regolith , astrobiology , asteroid , lunar craters , atmosphere (unit) , physics , geology , solar system , meteoroid , astronomy , astrophysics , meteorology
Frank et al. [1986b] and Frank and Sigwarth [1993] hypothesized the intense bombardment of the terrestrial atmosphere by small comets. Their model requires that the Moon is impacted by small comets (10 7 ‐10 8 g) at a rate of almost one per minute. We calculate that an object of this mass, even with an exceedingly low density and relatively low velocity, will nevertheless produce a crater at least 50 m in diameter. These craters will excavate immature lunar soil and produce a very bright spot with a diameter of at least 150 m. If low‐density comets exist that might not create deep craters [O'Keefe and Ahrens, 1982], they will nevertheless disturb the regolith sufficiently to create detectable bright spots. If the small‐comet hypothesis is correct then the near‐global lunar imaging returned by Clementine in 1994 should reveal ∼10 7 bright spots in locations where craters are not present in images acquired in the 1960's and early 1970's. We find no new bright spots in a carefully‐studied area of 5.2×10 4 km², so an upper limit to the current cratering rate by small comets is 33/yr, ∼10 4 below that expected if the small‐comet hypothesis were valid.