published Wednesday, August 3rd, 2011

Earth may have had two moons, astronomers say

  • photo
    This artist's rendering provided by Martin Jutzi and Erik Asphaug, University of California, Santa Cruz via Nature shows a simulation of a collision between the Moon and a companion moon, four percent of the lunar mass, about 4 billion years ago. Earth once had a second moon, until it made the fatal mistake of smacking its big sister, some astronomers now theorize. For awhile when the Earth was young, it had a big moon, the one you see now, and a smaller "companion moon" orbiting above. Then one day that smaller moon collided into the bigger one in what astronomers are calling the "big splat." (AP Photo/Martin Jutzi and Erik Asphaug, University of California, Santa Cruz via Nature)
    Photo by Associated Press /Chattanooga Times Free Press.

WASHINGTON (AP) — 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. But the smaller one smashed into the other in what is being called the "big splat."

The result: Our planet was left with a single bulked-up and ever-so-slightly lopsided moon.

The astronomers came up with the scenario to explain why the moon's far side is so much more hilly than the one that is always facing Earth.

The theory, outlined Wednesday in the journal Nature, comes complete with computer model runs showing how it might have happened and an illustration that looks like the bigger moon getting a pie in the face.

Outside experts said the idea makes sense, but they aren't completely sold yet.

This all supposedly happened about 4.4 billion years ago, long before there was any life on Earth to gaze up and see the strange sight of dual moons. The moons themselves were young, formed about 100 million years earlier when a giant planet smashed into Earth. They both orbited Earth and sort of rose in the sky together, the smaller one trailing a few steps behind like a little sister in tow.

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 couldn't 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 5,000 mph, but that's about as slow as possible when you are talking planetary smashups. It's slow enough that the rocks didn't melt.

And because the smaller moon was more than 600 miles wide, the crash took a while to finish even at 5,000 mph. 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 rocks and crust from the smaller moon would have spread over and around the bigger moon without creating a crater, as a faster crash would have done.

"The physics is really surprisingly similar to a pie in the face," Asphaug said.

And about a day later, everything was settled and the near and far sides of the moon looked different, Asphaug said.

Co-author Martin Jutzi of the University of Bern in Switzerland said the study was an attempt to explain the odd crust and mountainous terrain of the moon's far side. Asphaug noticed it looked as if something had been added to the surface, so the duo started running computer simulations of cosmic crashes.

Earth had always been an oddball in the solar system as the only planet with a single moon. While Venus and Mercury have no moons, Mars has two, while Saturn and Jupiter have more than 60 each. Even tiny Pluto, which was demoted to dwarf status, has four moons.

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

"We can't find anything wrong with it," Melosh said. "It may or may not be right."

Planetary scientist Alan Stern, former NASA associate administrator for science, said it is a "very clever new idea," but one that is not easily tested to learn whether it is right.

A second moon isn't just an astronomical matter. The moon plays a big role in literature and song. And poet Todd Davis, a professor of literature at Penn State University, said this idea of two moons — one essentially swallowing the other — will capture the literary imagination.

"I'll probably be dreaming about it and trying to work on a poem," he said.

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Salsa said...

Its just another goofy idea of the week. Wait until next week and another one will come along. I guess they have to do something to try to justify those government grants.

August 3, 2011 at 4:16 p.m.
EaTn said...

Well if we believe what the brilliant scientists say that the entire universe was formed from a tiny speck explosion, then it may be possible that the earth could once have had two moons.

August 3, 2011 at 8:09 p.m.
lkeithlu said...

What did you say your degree was in EaTn? Your comments show a lack of understanding of what science is, as well as ignorance about science in general.

August 3, 2011 at 8:40 p.m.
EaTn said...

Ikeithlu--sorry I awoke you from under your rock. My degree is in engineering--we're the science bunch that didn't drink the kool aid.

August 3, 2011 at 9 p.m.
lkeithlu said...

What kool aid? My degrees are in geoscience and chemistry. I was never served kool aid.

August 3, 2011 at 9:06 p.m.
aklashlee said...

Too funny, guys!

August 3, 2011 at 9:24 p.m.
EaTn said...

Well, we have a friendly mutual disagreement on some ideas, but it's not personal. At least on my part.

August 3, 2011 at 9:31 p.m.
lkeithlu said...

Not personal on mine either, but I'd like you to back what you say. If you are truly versed in science, as opposed to being just a well trained technician, you know what I mean.

Given, of course, you imply that I and all my scientist colleagues as well as my spouse are deluded, and that somehow only you know the Truth (TM).

August 3, 2011 at 9:41 p.m.
una61 said...

Sounds like another NASA "Back of the Napkin" idea developed during Happy Hour. Of course, the people in Dayton and Ooltewah would say its impossible since the earth is only 6000 years old.

August 4, 2011 at 12:01 a.m.
lkeithlu said...

It may have started that way una61-many good ideas do (think Harry Potter, though that was a coffee shop) I am inclined to think they spent a lot of time on it before announcing. It's a new theory, but a first step in trying to explain the differences between the surfaces. More evidence will support or falsify it.

That the moon was ripped from the earth in the first place is a relatively new idea (from the last few decades) which new evidence continues to support. Of course, plate tectonics was in its infancy when I was in school; now it's universally accepted.

Acceptance of an ancient earth and immutable physical laws is necessary for understanding much of the natural sciences.

August 4, 2011 at 7:29 a.m.
dao1980 said...

C'mon EaTn, an engineer that does not understand at least a few of the physical principles of gravity and accretion?

Now that fits my definition of scary, what is it that you "engineer"?

August 4, 2011 at 12:41 p.m.
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