HR: 1340h
AN: P23A-0186    [Abstracts]
TI: Atmospheric Variations and Meteorite Production on Mars
AU: * Chappelow, J E
EM: fsjec6@aurora.uaf.edu
AF: Earth and Planetary Remote Sensing, Geophysical Institute U. of Alaska Fairbanks 903 Koyukuk Dr., Fairbanks, AK 99775-7320 United States
AU: Sharpton, V L
EM: buck.sharpton@gi.alaska.edu
AF: Earth and Planetary Remote Sensing, Geophysical Institute U. of Alaska Fairbanks 903 Koyukuk Dr., Fairbanks, AK 99775-7320 United States
AB: Our previous work [1] indicates that the present martian atmosphere aerobrakes small percentages of small (0.1 -1.0 kg) carbonaceous chondrite, stony, and iron meteoroids to soft landings on the planet's surface. It also shows that meteorite production rates on Mars depend strongly on the martian atmospheric density. To examine these conclusions in detail, we constructed an atmospheric entry model for martian impactors and "scanned" it through a wide range of entry mass values, and appropriate ranges of entry velocity and angle. We weighted the results according to entry mass, velocity and angle probability distributions, and used them to estimate the fractions of statistically large populations of small (1 - 10⁹ kg) objects that soft-land, hard-impact, burn up, and skip out of the martian atmosphere. We repeated this procedure for four different martian atmospheres (2, 6, 20, 60 mbar). We find that nearly all small stony and iron impactors reach the martian surface, where they either soft-land or hard-impact depending on the density of the martian atmosphere. Only very small numbers skip out of the atmosphere and even fewer burn up. Production of both stony and iron meteorites increases sharply with increasing martian atmospheric density, essentially saturating when the atmospheric surface pressure is near 60 mbar. This is coupled with a corresponding decrease in stones and irons which hard-impact. These results were also used to investigate the entry and atmospheric conditions that may have produced Heat Shield Rock. We find that HSR almost certainly landed under an atmosphere at least as dense as today's, and quite probably one considerably denser. It probably struck the surface at a very shallow angle and ricocheted on impact. References: [1] Chappelow, J. E., Sharpton, V. L., Icarus, 2005, in press.
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 6225 Mars
DE: 6240 Meteorites and tektites (1028, 3662)
DE: 6297 Instruments and techniques
SC: Planetary Sciences [P]
MN: Fall Meeting 2005