spacetoday.net: Lunar rock study raises new questions about Moon formation model

Posted: Tue, Mar 27, 2012, 5:28 AM ET (0928 GMT)
Newly-published measurements of titanium concentrations in lunar rocks have led scientists to question the current model for the formation of the Moon. In a study published Sunday by Nature Geoscience, scientists reported that the relative abundance of two isotopes of titanium in lunar rocks collected during the Apollo missions is identical to that found in the Earth's mantle. That result, they argue, is at odds with the current model for the formation of the Moon after a Mars-sized planetesimal collided with the proto-Earth. That planetesimal is believed to have been chemically distinct from the Earth and would have accounted for 40 percent of the mass of the Moon, so scientists expected the relative abundances of those titanium isotopes to be different on the Moon than the Earth. The funding suggests that the formation model may need to be altered or possibly replaced with other mechanisms that can better explain the similar compositions.