Earth has just one Moon, right? Think again
“At any time there are one or two one-meter diameter asteroids in orbit around the Earth,” says Robert Jedicke, an astronomer at the Institute for Astronomy at the University of Hawaii. Jedicke used other methods to reach his findings due to most of the objects are too small to see. ”We know that there is a population of asteroids in orbit around the sun, that can come close to the Earth at some point in their orbit,” he says. ”But there’s a very small sub-component of that population that are on orbits that are very much like the Earth’s.”
The objects traveling by Earth go by ever so slowly, much like driving on a freeway and having someone pass you slightly faster than you are traveling.
“And by coming by so slowly, there’s a small chance they can be captured by the Earth’s gravity and go into orbit around the Earth,” says Jedicke.
Jedicke and his colleagues, Mikael Granvik from the University of Finland and Jeremie Vaubaillon of the Observatoire de Paris, wrote a program to calculate the amount that would be captured by the Earth’s gravitational pull and go into orbit. The teams calculations indicate the objects are no bigger than three feet across. Jedike also believes about every 50 years one the size of a garbage truck will go by ”and maybe once every 100,000 years, there’s be an asteroid that’s about the size of a football field in orbit around the Earth,”
The so called “minimoons” do not stick around for long, due in part by the Earth’s gravity, as Jedicke explains they are a loose capture. ”So loose that little gravitational nudges from the other planets in the solar system or from the moon can eventually just sort of dislodge them from the Earth’s gravity and allow them to go back into orbit around the Sun,” he added.
“We keep track of all the asteroids in the Earth’s vicinity,” says Paul Chodas, with the Near-Earth Object program at NASA’s Jet Propulsion Laboratory in Pasadena. “And there was one, very small asteroid which was discovered to be in orbit around the Earth. We didn’t know that right away…we thought it might be an old rocket stage or some other junk left over from the space program. But the trajectory indicated it was an asteroid.”