Earth has 1 moon and 2 co-orbital satellites. As you're probably aware, Earth has 1 moon, but did you know there are 2 additional asteroids locked into co-orbital orbits with Earth? They are called 3753 Cruithne and 2002 AA29.
3753 Cruithne is 5 km across, and sometimes called Earth's second moon although it clearly orbits the sun more then the Earth. It doesn't actually orbit the Earth, but has a synchronized orbit. It has an orbit that makes it look like it's following the Earth in orbit, but it's actually following the it's own, distinct path around the Sun. It looks to me that it takes 385 years to complete it's orbit and not the said 700. Not only is it not a moon it's not Earth's. Steven Fry lied to me!
If anything 2002 AA29 is earth's second moon, although it is to small to be a moon. It is only 60 meters across, and makes a horseshoe orbit around the Earth that brings it close to the planet every 95 years. In about 600 years, it will apear to circle Earth in a quasi-satellite orbit. It is constantly chasing us and might hit again! That's right I said again. Some time around 4.5 billion years ago it helped create the moon.
I also came across this in my search: Impact Risk
I couldn't make much sense of it but it looks like we might get hit by an asteroid.