The Earth's Moon is unusual

From a JPL news release:

New observations from NASA's Spitzer Space Telescope suggest that moons like Earth's - that formed out of tremendous collisions - are uncommon in the universe, arising at most in only 5 to 10 percent of planetary systems. ...

Scientists believe the Moon arose about 30 to 50 million years after our Sun was born, and after our rocky planets had begun to take shape. A body as big as Mars is thought to have smacked into our infant Earth, breaking off a piece of its mantle. Some of the resulting debris fell into orbit around Earth, eventually coalescing into the moon we see today. The other moons in our solar system either formed simultaneously with their planet or were captured by their planet's gravity.

A lot of things about the Earth-Moon system are very unusual, and they may even be essential for life on Earth. I think that scientists overestimate the possibility of intelligent life on other planets.