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My Two Moons- Did Earth Once Have A Second Moon?

03 August 2011
by Bridgette P. LaVictoire

Just think about it for a moment. Two glowing moons hanging above the Earth. It conjures up scenes like out of Elfquest or any other sci-fi or fantasy work that you can think of along those line, and maybe that was how it was once upon a time.

But, as things happen, there was the “big splat” and the Earth ended up with one great big if slightly lopsided satellite.

Astronmers are trying to figure out how to explain why the Moon’s far side is hillier than the side that faces the Earth all the time. As you can see, it looks like the moon is getting pied in the face.

This all happened about 4.4 billion years ago, according to the theory, which means that life had yet to begin on this planet. The moons were pretty young too, only about 100 million years old and were created when it is thought that a giant planet smashed into the Earth. The two would rise and set together sort of like a sisters walking together. According to the Huffington Post:

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.

Asphaug has said that the smaller moon was about 600 miles wide and even at 5,000 mph, the crash took a while. He compared the smaller moon to a rifle bullet saying “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.”

Because of the slowness, there would not have been a crater and the rocks would have spread around the larger moon. Asphaug said “the physics is really surprisingly similar to a pie in the face.” It took about a day for everything to settle on both sides of the moon and by then, it looked different.

Martin Jutzi, the co-author of the study, said that it was an attempt to explain the odd crust and mountainous terrain of the moon’s far side. Asphaug noticed that it looked like something had been added to the surface. This prompted the duo to run simulations of cosmic crashes.

The Huffington Post also reported that:

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 has people abuzz, especially at Woods Hole, Mass where a conference of scientists working on the next robotic mission to the moon were gathered. H. Jay Melosh of Purdue University said “We can’t find anything wrong with it. It may or may not be right.”

Planetary scientist Alan Stern stated that it was a very clever idea, but one that is not easily tested.

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