Daily Paper Summary: "Was Our Moon’s Formation Likely or Lucky?"

In a blog post on Astrobites, Michael Zevin, grad student at Northwestern University studying Physics and Astronomy, discusses the finding of two competing papers on the likelihood of our moon's formation.

Traditionally, scientists have accepted a theory in which a Mars-sized object (named Theia) collided with a young Earth, ripping off material from both objects into a disk of matter that clumped into the moon and Earth.  This theory was supported by the similarity of the composition of both the Earth and moon specifically in O-17 content.

Unfortunately, computer models of this collision propose that the majority of lunar material should come from Theia, not Earth.  This is clearly at odds with collision theory.  So, which is correct?

The blog post is inconclusive as paper 1 states that 5% of Earth-like planets have been struck by objects of similar composition.  Paper 2 claims that the figure is 50%.  

Each has validity, so we aren't really sure what to believe.  It's somewhat concerning that we still don't even know where our own Moon came from, but where there are questions, there is research funding!

Picture from http://www.novacelestia.com/images/earth_impact_moon.jpg
Blog post: http://astrobites.org/2015/04/08/was-our-moons-formation-likely-or-lucky/