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Fri, Aug 05, 2011 - Page 6　News List

Earth had two moons, study says

‘BIG SPLAT’:A new study contends that about 4.4 billion years ago, two moons orbited Earth until they collided, leaving one bulkier, slightly lopsided satellite


In a spectacle that might have beguiled poets, lovers and songwriters if only they had been around to see it, Earth once had two moons, astronomers now think. However, the smaller one smashed into the other in what is being called the “big splat.”




Outside experts said the idea makes sense, but they are not completely sold yet.


The smaller one was a planetary lightweight. The other was three times wider and 25 times heavier, its gravity so strong that the smaller one just could not resist, even though it was parked a good bit away.

“They’re destined to collide. There’s no way out ... This big splat is a low-velocity collision,” said study co-author Erik Asphaug, a planetary scientist at the University of California, Santa Cruz.

What Asphaug calls a slow crash is relative: It happened at more than 8,050kph, but that is about as slow as possible when you are talking planetary smashups. It is slow enough that the rocks did not melt.

And because the smaller moon was more than 965km wide, the crash took a while to finish even at 8,050kph.

Asphaug likened the smaller moon to a rifle bullet and said: “People would be bored looking at it because it’s taking 10 minutes just for the bullet to bury itself in the moon. This is an event if you were looking at, you’d need a big bag of popcorn.”






The theory was the buzz this week in Massachusetts, at a conference of scientists working on NASA’s next robotic mission to the moon, said H. Jay Melosh of Purdue University.


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