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Did the Earth Once Have Two Moons?

Did the Earth Once Have Two Moons?
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Literally earth-shattering news: Once upon a very long time ago, the earth may have had two moons.

The two satellites were formed after a “Mars-size protoplanet” collided with the earth late in its formation period. Then, according to a recently published study in Nature, the two moons merged in a “slow-motion collision that took several hours to complete,” with the result a very visible difference between the two sides of the moon:

The Moon’s visible side is dominated by low-lying lava plains, whereas its farside is composed of highlands. But the contrast is more than skin deep. The crust on the farside is 50 kilometres thicker than that on the nearside. The nearside is also richer in potassium (K), rare-earth elements (REE) and phosphorus (P) — components collectively known as KREEP. Crust-forming models show that these would have been concentrated in the last remnants of subsurface magma to crystallize as the Moon cooled.

Erik Asphaug, a planetary scientist at the University of California, Santa Cruz, and Martin Jutzi, now of the University of Berne, used computer models to account for why the moon’s two sides are so different. In the course of their research, they theorized that “something ‘squished’ the late-solidifying KREEP layer to one side of the Moon [the nearside], well after the rest of the crust had solidified.” An impact, says Asphaug, is the most likely explanation.

Traditional theories have argued that “the infant Moon rapidly swept up any rivals or gravitationally ejected them into interstellar space.” The new theory rather contends that one body did survive, “parked in a gravitationally stable point in the Earth–Moon system.” After all, as Asphaug points out — and as anyone who’s been in an auto accident that’s more than a little fender-bender — a collision, by definition, only occurs on one side.

The scientists’ computer model suggests that the smaller “sister moon” was about one-thirtieth of the mass of the Moon, around 1,000 kilometres in diameter. So the smaller moon could have survived as a separate body long enough for its upper crust, and that of the (larger) Moon, to solidify, while the Moon’s inner KREEP layer remained liquid (just as — with apologies to any who find this comparison a bit mundane — while the top of a pan of brownies hardens after you take it out of the oven, the inside may still have more of the consistency of batter).The smaller moon was in what’s called a Lagrangian point, a “gravitationally stable point in the Earth-Moon” system about 60 degrees in front or behind the Moon’s orbit.

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Photo by armaggesin

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61 comments

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12:26AM PDT on Aug 18, 2011

This is a very interesting theory.
We probably will never know if it was true.

3:04AM PDT on Aug 13, 2011

Thanks for the article.

7:54PM PDT on Aug 11, 2011

thanks for the article.

6:16PM PDT on Aug 8, 2011

Maybe the moon was a sun , i think thousands a year ago or a star as the sun is know.

5:37PM PDT on Aug 8, 2011

Incredible speculation with no way of proving anything and yet people choose to believe this sort of science over God (again, no way to prove He exists).

They'll be saying that the universe was created by an enormous explosion, next.....ha ha.

God seems much more logical to me but each to his own.

4:20PM PDT on Aug 8, 2011

Man is already beginning to exploit the moon, because he can.

They have set off bombs on the moon.

Two moons?

Will we even have one moon left?

1:40PM PDT on Aug 8, 2011

i think it's very possible, and would love to know

1:29PM PDT on Aug 8, 2011

this type of info is a bit intriguing and a bit scary

1:45AM PDT on Aug 8, 2011

One hypothesis is that if the 2 moons had remained there would be no life on this planet.

10:18PM PDT on Aug 6, 2011

Well if there were still 2 moons we'd have to change a few song lyrics - 'Two moons you saw me standing alone' .... 'Blue moons' etc. Seriously I'd love to visit another planet with several moons . I love seeing ours in the night sky so can only imagine how beautiful and magical seeing several moons waxing and waning would be - but alas not in my life time .. oh well I can dream.

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