Titanium Isotopes Provide Clues to Lunar Origin
The Moon may have formed by the
impact of a Mars-sized object with Earth.
Planetary accretion models suggest that
the impactor and Earth would have had
different isotopic compositions…
…but titanium has the same isotopic
composition in both Earth and Moon.
The dynamics of planet formation and of
the giant impact need a closer look.
http://www.psrd.hawaii.edu/May12/Ti-isotopes-EarthMoon.html