Having a moon like ours makes us very special, cosmically speaking. This is according to proper scientists at the Universities of Arizona and Florida (as opposed to Mystic Meg), who've been searching the universe with the Spitzer space telescope for other planetary systems like ours.
More: http://www.theregister.co.uk/2007/11/22/collisions_moon/
Moons like the Earth's - which are formed in catastrophic collisions - are extremely rare in the Universe, a study by US astronomers suggests.
The Moon was created when an object as big as the planet Mars smacked into the Earth billions of years ago.
More: http://news.bbc.co.uk/2/hi/science/nature/7104558.stm
The solar system might once have had another planet named Theia, which may have helped create our own planet's moon.
Now two spacecraft are heading out to search for leftovers from this rumored sibling, which would have been destroyed when the solar system was still young.
"It's a hypothetical world. We've never actually seen it, but some researchers believe it existed 4.5 billion years ago — and that it collided with Earth to form the moon," said Mike Kaiser, a NASA scientist at the Goddard Space Flight Center in Maryland.
Theia is thought to have been about Mars-sized. If the planet crashed into Earth long ago, debris from the collision could have clumped together to form the moon. This scenario was first conceived by Princeton scientists Edward Belbruno and Richard Gott.
Many researchers now figure that indeed some large object crashed into Earth, and the resulting debris coalesced to form the moon. It is unclear though if that colliding object was a planet, asteroid or comet.
More: http://www.space.com/scienceastronomy/090413-mm-stereo-lagrange.html (http://www.space.com/scienceastronomy/090413-mm-stereo-lagrange.html)
I thought that the Moon was supposed to be composed partly of broken off Earth and partly from Theia, so we are looking at some of it. But of course where is the remainder?
carole
Boffins: Ancient world smashed into us to create Moon
A pair of NASA "space weather" monitoring spacecraft are having something of a change of pace, as they search for evidence of a long-lost world which may once have crashed into the Earth, and so formed the Moon.
The two probes in question are those of the space agency's Solar Terrestrial Relations Observatory (STEREO) programme, intended to gain a side view of the sun's interaction with Earth.
More: http://www.theregister.co.uk/2009/04/14/nasa_stereo_theia_lagrange_scan/