Earth's Moon is a rare cosmic occurrence, according to a study by US astronomers, the BBC reported.

The Moon was created when an object as big as the planet Mars crashed into the Earth billions of years ago, throwing debris into orbit, some of which eventually consolidated to form our Moon.

"When a moon forms from a violent collision, dust should be blasted everywhere. If there were lots of moons forming, we would have seen dust around lots of stars - but we didn't," according to the study's author, Nadya Gorlova.

The collision has occurred when the Sun was only 30 million years old, and the astronomers looked at infrared signatures of 400 solar systems aged 10 to 50 million years.

"We found about two to four [dusty] objects, but only one fits all the characteristics of a moon collision. The dust is at the right temperature and at the right distance," Dr Gorlova told BBC News.

"We don't know that the collision we witnessed around the one star is definitely going to produce a moon, so moon-forming events could be much less frequent than our calculation suggests," said study co-author George Rieke.

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