A team of astronomers at the University of Helsinki in Finland, headed by Mikael Granvik, have run computer simulations determining that Earth has more than one moon...kind of. Thousands of tiny asteroids, pulled into Earth's orbit, have been found.
According to a newly published article on New Scientist, evidence of the Earth snagging new moons has been collected as early as 2006, when NASA employee Paul Chodas analyzed what was thought to be remnants of a space shuttle's rocket stage, but turned out to be an asteroid a few meters in width, orbiting the Earth. It had been long theorized that small space debris such as asteroids did sometimes get caught in Earth's gravitational field and act as temporary moons, and now Granvik and his team have the data to back it up.
Granvik's team has found that at any given time, there is at least one asteroid in Earth's orbit, as well as thousands of smaller rocks and space debris. The reason these asteroids have gone long undetected is because most of them tend to be no bigger than a meter in width, and are very hard to spot when moving so fast. In order to be caught in the Earth's gravity, the asteroid must be moving as fast as the Earth is, and be close enough (five to ten times the distance as the moon is from Earth) to be snared.
Granvik suggests that since these rocks are so close to Earth and are trackable, we could one day be able to pluck the asteroids from their orbits and bring them back to Earth for study. Asteroids hold the key to learning more about how the universe was formed, as they are pieces of ancient space objects. A pure asteroid, undamaged from entering the Earth's atmosphere, has never been studied before. Plans to retrieve these asteroids are already being drawn up by NASA, the European Space Agency, and JAXA, the Japanese space agency.
The Earth is no stranger to asteroids. A 2008 incident was recorded by NASA, showing an asteroid that came within 560,000 miles of Earth. In 2011, an asteroid as large as an aircraft carrier passed only 201,000 miles away from Earth, in between the Earth and the moon, making it the closest an asteroid has ever come to hitting the Earth in modern times.