The Moon was created when an object as big as the planet Mars smacked into the Earth billions of years ago.
The impact hurled debris into orbit, some of which eventually consolidated to form our Moon.
The Astrophysical Journal reports that just 5-10% of planetary systems in the Universe have moons created this way.
"When a moon forms from a violent collision, dust should be blasted everywhere," said lead author Nadya Gorlova of the University of Florida in Gainesville, US.
"If there were lots of moons forming, we would have seen dust around lots of stars - but we didn't."
Scientists suggest our Moon is pretty unique
Posted on Tuesday, Nov 27 2007 @ 05:20 CET by Thomas De Maesschalck