Earth May Once Have Had Two Moons

AaronW writes "According to a story at space.com, Earth may once have had two moons. The smaller moon, estimated to be 750 miles (1200km) wide and only 4% of the mass of the larger moon, crashed into the far side of the larger moon which caused the features we see today on the moon. The surface of the far side of the moon is quite different than the side facing the earth, having a different composition and a much rougher terrain."

Gravity not visible surface

[perpenso]

I don't think you can use the observable earth as an indication of the protection offered. I would expect that the earth's "gravity well" (sorry, a more proper term escapes me at the moment) would be more relevant. That said I am quite suspicious of your overall approach. It seems to be commonly accepted that Jupiter provides the earth with significant protection, now consider the percentage of the sky hemisphere that jupiter occupies.