EAPS

Robin Canup, Southwest Research Institute
April 8 | 3:45 - 5:00 pm | 54-100
Host: Jack Wisdom

Origin of the Earth and Moon: New Results and Open Issues

It is thought that the Moon formed by a giant impact with the Earth, although how such an event can explain the close compositional similarities between the Moon and the Earth's mantle remains a matter of active debate. Canonical impacts by a Mars-sized impactor produce a protolunar disk derived primarily from the impactor's mantle. This would be consistent with Earth-Moon isotopic similarities if the impactor had a very similar composition to the Earth. However, in recent years several arguments have been advanced that imply such a compositional match is very unlikely. This has motivated new models involving, e.g., post-impact equilibration of the disk and planet vapor components prior to the Moon's accumulation, or high-angular momentum impacts that produce disks with compositions that are nearly identical to that of the post-impact planet. While such models provide new ways to account for Earth-Moon compositional similarities, they each require a secondary process after the impact itself, resulting in a less probable event overall. Alternatively, the compositional difference between the Moon-forming impactor and the Earth may have been less than suggested by recent estimates.