The Survivor? Photo: NASA

Scientists have wondered why the  side of the moon that always faces Earth (the near side) is  relatively low and flat, while  the far side has a thicker crust and is mountainous.

There is still so much we don’t know.

I read this past week on  National Geographic News that scientists created a computer model that explains this difference with the theory that a smaller “companion moon” collided with our moon’s far side early in its history.

A slow-motion collision (at about 4,400 miles or 7,081 kilometers an hour) would have left our familiar moon with more varied elevations as it splattered that side with hard rocky material. The smaller moon (about a third the size of the other) would have been destroyed.

That slow collision would mean that it wouldn’t melt rock or carve out a crater.

The model shows the two moons co-existing for about 80 million years, each in its own stable orbit. But then natural gravitational interactions with Earth caused both moons to move away from Earth. Into play comes the sun’s gravitational pull which shifted the smaller moon’s orbit.  Crash.

The fallout of this would have sent lots of lunar debris into space for up to a million years after the event. Pieces 62 miles (100 kilometers) across to dust would have been falling – but there would have been no life yet on Earth to witness it.

The new theory creates new problems to solve. (Why does the far side have a lot of aluminum instead of being low in aluminum, like our current moon’s interior?)

Would we have had two full moon dates to blog about here?

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