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Earth’s 2nd moon

Photo: NASA

is estimated to have been 750 miles (1,200 kilometers) wide and trailed the existing moon by approximately 60 degrees. It is thought to have orbited the Earth for tens of millions of years before catastrophically slamming into the remaining moon.

The two moons coexisted peacefully for about 80 million years, each in its own stable orbit. The moons were the same color and composition, with the existing moon about three times larger than the other.

Our remaining moon has two faces. The surface of the near side is mostly low and flat, while the far side, or the dark side, is mountainous, elevating 1.2 miles (1.9 km). Computer simulations suggest that the second moon essentially pancaked itself against its larger companion. The collision would have been relatively slow, 4,500 to 6,700 miles per hour (7,200 to 10,800 kph), allowing its matter to splatter across our moon as a thick extra layer of solid crust, tens of miles thick, instead of forming a crater. That titanic clash that could explain why the two sides of the surviving lunar satellite are so different from each other, leaving the far side splattered with especially hard rocky material that now forms the current lunar highlands.

Imagine a ball of Gruyere colliding into a ball of cheddar.

 

 

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