Moon Formed From Head-On Collision, Computer Simulations Suggest

Artist's rendering shows planetary collision near the
star Vega. The Moon may have formed from the debris
 of such an impact between Earth and a Mars-sized
body, NASA says.

Some 4.53 billion years ago, a Mars-sized impactor slammed into Earth, forming a young, molten moon. But was it a head-on collision or a glancing blow?

New computer simulations argue for the former, indicating that the impactor scored a direct hit, crashing into Earth at a steeper angle and with a higher velocity than previously thought. The resulting smashup would have ejected far more Earth debris into space than other models have indicated, with much hotter temperatures. And that would mean the moon formed from more Earthlike material than previously thought.

The origin of the impactor itself remains an open question. The slow impact velocity of previous models requires it to have originated from an orbit very near Earth, while the new model allows for an origin from more far-flung parts of the solar system, researchers report in an upcoming issue of Icarus.