Moon Formation From Giant Hit-and-run Impact
July 30, 2012

Moon Formation May Have Been The Result Of Larger, Faster Planet Collision

redOrbit Staff & Wire Reports - Your Universe Online

While scientists tend to accept the theory that the Moon was formed following a collision between a young Earth and a second planet, new research published online earlier this month suggests that the impactor might have been larger and traveling faster than previously believed.

Current theory suggests that Earth's satellite was formed when the protoplanet was hit by a second world, believed to have been about the size of Mars, billions of years ago, Evan Ackerman of DVice wrote on Thursday.

Now, however, Andreas Reufer of the University of Bern in Switzerland and a team of colleagues are claiming that the planet was actually larger, moving at faster speeds, and colliding with the Earth at a steeper angle than the current model would suggest. Furthermore, the object responsible for the collision may still be at large.

"It also would have transmitted significantly more energy into the Earth, heating up the mantle to 10,000 degrees," Ackerman said. "It's a lot more extreme of an idea, but it's the only model that accurately explains why the Moon seems to be made entirely of stuff from the Earth and not from any rogue planet material."

The problem with the current theory is that with a slower, grazing impact, the majority of the debris that would have eventually formed into the Moon would have originated from the planet which collided with Earth, the MIT Technology Review explained.

The hypothesis submitted by Reufer's team fixes that problem, in that the additional velocity would have caused most of the impact debris to escape, while the debris left behind would have been a mixture of material from that planet and from Earth, "with an isotopic content that matches the observed signatures here and on the Moon," they said.

"Of course, the debris that escaped would have carried away angular momentum as well as mass. This makes such a scenario challenging to model because it is hard to find a suitable set of starting conditions -- mass, angular moment, impact angle, etc. -- that produce a realistic Earth-Moon system. In fact, astronomers have discounted this scenario in the past for precisely this reason," the MIT website added.

However, Reufer and his colleagues decided to use improved simulation techniques to return to the hypothesis. They created a model that consisted of approximately 500,000 particles. When the Moon is formed, it ends up being roughly 10,000 particles, and the simulation can produce Earth and Moon like systems "for a reasonable set of starting conditions, while at the same time reproducing the observed isotopic signatures," they said.

Their work, which is set to be published in the journal Icarus, also suggests that the impactor most likely loss just a little bit of material and would have continued on after the collision, according to BBC News reports. Ackerman also suggests that the rogue planet may still be around and traveling throughout space today.

Further analysis of elements contained within samples brought back from the moon, as well as additional computer simulations, are necessary to fully explore Reufer's theory, the British news agency said. Likewise, the MIT News Review said that the researchers need to explain what would have happened to the impact debris which escaped from Earth's orbit -- which could theoretically be done by testing meteors to search for its isotopic signature.