Earth has a "second moon." Asteroid 2003 YN107 is looping around our planet once a year. Measuring only 20 meters across, the asteroid is too small to see with the unaided eye—but it is there. This news, believe it or not, is seven years old."2003 YN107 arrived in 1999," says Paul Chodas of NASA's Near Earth Object Program at JPL, "and it's been corkscrewing around Earth ever since." Because the asteroid is so small and poses no threat, it has attracted little public attention. But Chodas and other experts have been monitoring it. "It's a very curious object," he says.Most near-Earth asteroids, when they approach Earth, simply fly by. They come and they go, occasionally making news around the date of closest approach. 2003 YN107 is different: It came and it stayed."We believe 2003 YN107 is one of a whole population of near-Earth asteroids that don't just fly by Earth. They pause and corkscrew in our vicinity for years before moving along."These asteroids are called Earth Coorbital Asteroids or "coorbitals" for short. Essentially, they share Earth's orbit, going around the Sun in almost exactly one year. Occasionally a coorbital catches up to Earth from behind, or vice versa, and the dance begins: The asteroid, while still orbiting the sun, slowly corkscrews around our planet. "These asteroids are not truly captured by Earth's gravity," notes Chodas. "But from our point of view, it looks like we have a new moon."Astronomers know of at least four small asteroids that can do this trick: 2003 YN107, 2002 AA29, 2004 GU9 and 2001 GO2. "There may be more," says Chodas. He believes the list will grow as asteroid surveys improve in sky coverage and sensitivity.At the moment, only two coorbitals are actually nearby: 2003 YN107 and 2004 GU9. The others are scattered around Earth's orbit.

2004 GU9 is perhaps the most interesting. It measures about 200 meters across, relatively large. And according to calculations just published in the Monthly Notices of the Royal Astronomical Society (S. Mikkola et al., 2006) it has been looping around Earth for 500 years--and may continue looping for another 500. It's in a remarkably stable "orbit."Right now, however, researchers are paying more attention to 2003 YN107 for one simple reason: it's about to depart. The asteroid's corkscrew path is lopsided and on June 10th it will dip within 3.4 million km of Earth, slightly closer than usual. Earth's gravity will then give the asteroid the nudge it needs to leave. "This is a chance to observe one of these asteroids [on the way out]," explains Chodas.

View: Full Article | Source: NASA

So, we have three moons right now? Dude, that is just nifty!

I want to be the first astronaut on the moon Asteroid 2003 YN107. Although you will drop off with one big step. :|

Well not really. As the article says they haven't actually been captured by Earth's gravity, so in the strictest sense they aren't truely moons.




Too late. It's moving away now.

Don't go killing my buzz. They are only temporary moons, true. And 2003 is about to leave us, but the other should be around 500 more years, so until then we'll have two moons!

Are they even big enough to be considered moons? Or merely natural satellites? Anyhow, we have two moons! Nanners!

I thought that a *Moon* had to be a minimum of 40kms in diameter otherwise they are classified as a *satellite*?

The terms "moon and "natural satellite" are completely interchangable, so if it is a moon it is a natural satellite and vice versa. There is currently no lower size limit to the definition of satellite, although particles of dust (such as those found in the rings of Saturn) would certainly not be considered moons.

Astronomers argue over whether objects such as 2003 YN107 are truely satellites as they are not actually in orbit around a planet. The phrase quasi-planet has come into use to describe them.

An interesting article (and the source of my information) can be found here: Space.com - What is a Moon?

Well still its pretty sweet I am going to step on the other one (PS if they do become moons i hope we give it a more orginal name other than just Moon 2)

For a while it will be worse than that!

Until the International Astronomical Union decided on a permanent name it would be known as S/XXXX E1 (the XXXX would be replaced by the year of discovery). The S would signify that it is a satellite, the E would signify that the planet it orbits is Earth and the 1 following the E would signify that it was the first satellite orbiting the Earth that year.

There has been an ongoing debate for a long time about Pluto and whether it should be considered a planet, much less a moon. Some want to degrade its status to captured asteroid or ice ball, or whatever. Interestingly, though, Pluto, tiny as it is, even has it's own satellite - Charon.

So if Pluto loses planet status, I wonder what we would consider its "moon." Random captured space debrise?

All three of Plutos satellites would still be considered satellites. Asteroids have satellites too, for example Ida and it's satellite Dactyl.


Credit: NASA/JPL-Caltech