Space Collisions

This is a pretty exciting article about a new paper coming out in Nature regarding what scientists now believe happened to Mars 4 billion years ago. They speculate that a Pluto-sized object hit Mars and created the crater that is the Mars lowlands, which is also the largest crater in the solar system. This, though, was really interesting and the first I'd heard the theory (though I don't know much about scientific theories of planets, so that doesn't mean much).

About the same time, more than four billion years ago, Earth is believed to have been hit by a Mars-size object, which created the Moon, and signs of a giant impact have also been detected on Mercury.

If that's true, what a fortunate event, for if my 5-year-old memory serves me correctly, the moon's gravity plays an integral role in the Earth's ocean's tides.