HR: 08:45h
AN: U21E-04 [Abstracts]
TI: Craters Clusters on Mars: Atmospheric Dispersion of Small Impactors
AU: * Melosh, H J
EM: jmelosh@lpl.arizona.edu
AF: Lunar and Planetary Lab, University of Arizona, Tucson, AZ 85721, United States
AU: McEwen, A S
EM: mcewen@pirl.lpl.arizona.edu
AF: Lunar and Planetary Lab, University of Arizona, Tucson, AZ 85721, United States
AB:
The HiRISE imager aboard the Mars Reconnaissance Orbiter has imaged 18 of the 20 small dark areas that
correspond to fresh impact scars on the surface of Mars, reported by Malin et al in 2006 to have appeared after
1999. Operating at a resolution of approximately 30 cm/pixel, HiRISE revealed that the largest of these craters
contains eolian ripples and is probably more than just a few years old. The other dark halos often contain
clusters of small impact craters with diameters ranging from 1 to 30 m in diameter. About half of these are
clusters of 3-10 craters, with one cluster of more than 1,000 craters near 10 m diameter. The dispersion of the
clusters is typically less than 100 m, although the largest cluster, whose craters exhibit clear signs of oblique
impact, spreads almost 500 m. The size and dispersion of these clusters is consistent with dispersion of
incoming meteoroids by atmospheric fragmentation at an altitude of about 20 km. Modeling of the atmospheric
fragmentation and impact process shows that the size of the incoming meteoroids is in the range of 0.3 to 1 m
(15 m for the largest, older crater), bulk density near 2000 kg/m3 and strength 0.5 to 1 bar, consistent with
the properties of terrestrial or Venusian stony impactors. Small crater clusters on Mars are thus consistent with
the theory for atmospheric dispersion of impactors observed on Earth and Venus, whose mean dispersions are
typically 1 km and 10 km, proportional to the square root of surface atmospheric density.
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 6022 Impact phenomena (5420, 8136)
DE: 6225 Mars
DE: 6240 Meteorites and tektites (1028, 3662)
DE: 8136 Impact phenomena (5420, 6022)
SC: Union [U]
MN: 2007 Fall Meeting