Giant Impact Hypothesis - Energetic Aftermath

Energetic Aftermath

In 2001, a team at the Carnegie Institute of Washington reported the most precise measurement of the isotopic signatures of lunar rocks. To their surprise, the team found that the Apollo rocks carried an isotopic signature that was identical with rocks from Earth, and were different from almost all other bodies in the Solar System. Since most of the material that went into orbit to form the Moon was thought to come from Theia, this observation was unexpected. In 2007, researchers from the California Institute of Technology showed that the likelihood of Theia having an identical isotopic signature as the Earth was very small (<1 percent). Instead, they proposed that in the aftermath of the giant impact, while the Earth and the proto-lunar disk were molten and vaporized, the two reservoirs were connected by a common silicate vapour atmosphere, and that the Earth–Moon system became homogenized by convective stirring while the system existed in the form of a continuous fluid. Such an "equilibration" between the post-impact Earth and the proto-lunar disk is the only scenario capable of explaining the isotopic similarities of the Apollo rocks with rocks from the Earth's interior. For this scenario to be viable, however, the proto-lunar disk must exist for a time period of ~100 years. Work is ongoing to determine whether or not this is possible.