Interesting Info - Another small moon may have orbited our Earth before the satellite finally hit a larger moon and formed the moon that always orbits the Earth as it does now. The incredibly powerful collision of the two moons may explain why the two sides of the lunar satellite that we see today are so different from each other.
Although not yet proven, the idea of “two moons” put forward by Martin Jutzi and Erik Asphaug from the University of California at Santa Cruz has attracted the attention of many astronomers. This theory may explain why the side of the moon facing Earth is dominated by a "sea" of ancient lava that has hardened and formed a smooth and broad surface. In contrast, the back side of the moon is filled with mountainous highlands.
“This idea is so intriguing,” said David Smith, GRAIL deputy principal investigator at MIT. "This idea could be an explanation for one of the biggest puzzles in the Earth-moon system, namely the asymmetric shape of the moon."
This new study reveals the possibility that, in the past, the Earth once had two moons. Astronomers say the second moon circling Earth may be 1,200 kilometers in diameter and could have formed from the same collision between a planet and a Mars-sized object that is thought to have helped create the moon we see in the sky today, some four billion years ago.
The gravitational tug-of-war between the earth and the moon slows its rotation, so that what is now always visible is only one side of the moon. The other side of the moon remained a mystery for centuries until 1959 when the Soviet space probe, Luna 3, captured it for the first time. This side is often mistakenly called the dark side even though the face of the moon also experiences day and night like the side we see.
The face of the other side of the moon is very different from the closer side. For example, widespread volcanic rock plains, named “maria” or seas in Latin, cover most of the nearby lunar hemisphere, but only a few maria are visible on the far side. The surface of the moon's near side is generally low and flat, while the far side is characterized by high hills, with the moon's surface rising an average of 1.9 kilometers.
Computer simulations predict that the second moon will expand like a cake when it collides with the larger moon. "This explains why the moon seems to have two different faces," said Erik Asphaug.
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