Scientific Colloquium
April 13, 2007

"New Views on the Lunar Late Heavy Bombardment"

The Lunar Late Heavy Bombardment (LHB) defines a time 3.8-3.9 Gy ago when the basins on the Moon with known ages were formed (e.g., Imbrium, Orientale).  Some suggest these basins were created by the tail end of a declining impactor population produced by planet formation processes. Others argue they were produced by a spike in the impactor flux 3.9 Gy ago.  Using new numerical simulations, I will show the former scenario cannot work, and that the LHB was instead the byproduct of a terminal cataclysm produced by a sudden change in the orbital configuration of the Jovian planets.  The model that I will present is compelling not only because it reproduces Lunar LHB constraints but also because it explains the orbits of the Jovian planets and small body reservoirs in the outer solar system (e.g., Trojans of Jupiter and Neptune, the Kuiper belt and scattered disk, the irregular satellites of the giant planets, and the curious presence of dormant comets in the outermost regions of the asteroid belt).  These accomplishments are unique among models of outer solar system formation.

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