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Monday, November 14, 2011
4:00 PM - 5:00 PM
Arms 155 (Robert P. Sharp Lecture Hall)

Geological and Planetary Sciences Seminar

Exploring the Early Bombardment of the Moon and Terrestrial Planets
Bill Bottke, senior research scientist, Southwest Research Institute,
The early bombardment history of the Inner Solar System is recorded in a number of interesting places (e.g., the surprisingly high abundance of highly siderophile abundances found in the mantles of Earth, Moon, and Mars, the observed impact basins found on Mercury, the Moon and Mars, various properties of main belt asteroids and meteorites, etc.). To date, two dominant scenarios have been used to explain these constraints: (i) most impacts came from the tail end of a monotonically-decreasing impactor population created by planet formation processes, and (ii) most impacts were produced by a terminal cataclysm that caused a spike in the impactor flux starting ~4 Gy ago. Interestingly, we find that both scenarios are needed to explain observations. For (i), we will show that leftover planetesimals were long-lived enough to hit various worlds long after the end of core formation. The record left behind can be used in interesting ways to probe the nature of terrestrial planet formation. For (ii), we will explore new applications of the so-called Nice model, which provides a plausible dynamical mechanism for producing late giant planet migration as well as a "late heavy bombardment". We will show that most LHB-era impactors came from an unexpected source, and that they continued to hit Earth well after basin formation terminated on the Moon.
For more information, please contact Liz Boyd by phone at 626-395-6070 or by email at