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L. Dones (SwRI), B. Gladman (UBC), H. F. Levison (SwRI), J. A. Burns (Cornell)
Ejecta from early, large impacts on the terrestrial planets may still be present near the surfaces of the Moon, Mars, and Mercury. Armstrong et al. (Icarus 160, 183, 2002) modeled the transport of ejecta from Earth, Mars, and Venus to the Moon. Since the discovery of rocks from the Hadean Earth would be of great geochemical and exobiological importance, Armstrong et al. argued that a lunar sample return mission to find such ejecta might be warranted. As part of an ongoing study of the transport of impact ejecta from the Earth throughout the Solar System, we are calculating the fraction of ejecta that reach Mars as a function of terrestrial launch speed. In general, the rate at which ejecta reach Mars is roughly constant with time after the impact (cf. Gladman, Icarus 130, 228, 1997). For very low-speed ejecta, the fraction of Earth ejecta reaching Mars, f, is of order 10-4 per Myr (Mileikowsky et al., Icarus 145, 391, 2000). As the impact speed on Earth increases, more ejecta reach Mars. For example, for v\infty =~3~km/s, corresponding to a launch speed of 11.6 km/s (compared with Earth's escape speed of 11.2 km/s), our preliminary results suggest that f ~10-3~/Myr. We will discuss the transport efficiency and the issue of whether life could have survived its voyage between the planets and its landing on Mars, for different assumptions about Mars' early atmosphere. This work has been supported by a grant from the NASA Exobiology program.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.