Washington, Nov 21: New observations from NASA's Spitzer Space Telescope suggest that moons like Earth's, that have been formed out of tremendous collisions, are uncommon in the universe.

"When a moon forms from a violent collision, dust should be blasted everywhere," said Nadya Gorlova of the University of Florida, who is also the lead author of a new study on the topic. "If there were lots of moons forming, we would have seen dust around lots of stars, which we didn't," she added.

Scientists believe that the moon formed after a planetary body as big as Mars smacked into our infant Earth. This impact had probably broken off a piece of the planet's mantle. Some of the resulting debris fell into orbit around Earth, eventually forming into the moon we see today.

As for the other moons in our solar system, they either formed simultaneously with their planet or were captured by their planet's gravity.

The new observations by the research team looked for the dusty signs of similar smash-ups around 400 stars that are all about 30 million years old, roughly the age of our sun when Earth's moon formed.

What they found was that only 1 out of the 400 stars is immersed in the telltale dust. Taking into consideration the amount of time the dust should stick around, and the age range at which moon-forming collisions can occur, the scientists then calculated the probability of a solar system making a moon like Earth's to be at most 5 to 10 percent.