The Big Splat!

NASA’s GRAIL (Gravity Recovery and Interior Laboratory) mission may pull back the curtain on the Moon’s mysterious “far side.”  Catch the launch of GRAIL on September 9th, 2011 at 8:12am CST – Live feed available on NASA TV.

If a paper published recently in the journal Nature* is right, two moons once graced our night skies. The proposition has not been proven, but has drawn widespread attention.

The Big Splat

“It’s an intriguing idea,” says David Smith, GRAIL’s deputy principal investigator at MIT. “And it would be a way to explain one of the great perplexities of the Earth-Moon system – the Moon’s strangely asymmetrical nature.  Its near and far sides are substantially different.”

The Moon’s near side, facing us, is dominated by vast smooth ‘seas’ of ancient hardened lava. In contrast, the far side is marked by mountainous highlands. Researchers have long struggled to account for the differences, and the “two moon” theory introduced by Martin Jutzi and Erik Asphaug of the University of California at Santa Cruz is the latest attempt.

Scientists agree that when a Mars-sized object crashed into our planet about 4 billion years ago, the resulting debris cloud coalesced to form the Moon. Jutzi and Asphaug posit that the debris cloud actually formed two moons. A second, smaller chunk of debris landed in just the right orbit to lead or follow the bigger Moon around Earth.

“Normally, such moons accrete into a single body shortly after formation,” explains Smith. “But the new theory proposes that the second moon ended up at one of the Lagrange points in the Earth-Moon system.”

Lagrange points are a bit like gravitational fly traps. They can hold an object for a long time–but not necessarily forever. The second moon eventually worked its way out and collided with its bigger sister. The collision occurred at such a low velocity that the impact did not form a crater. Instead, the smaller moon ‘went splat,’ forming the contemporary far side highlands.

In short, the lunar highlands are the lost moon’s remains

Read the Full article at science.nasa.gov

For more information about our cosmic neighbor’s composition, visit the Starship Gallery at Space Center Houston.  Home to the world’s largest collection of Moon rocks on public display, including a 1.5 billion year old lunar touchstone!  Save $5 off admission when you buy tickets online!