It turns out Earth's single giant moon might not be the only one floating around out there. In fact, at any given time, there may be at least one other "minimoon" orbiting our planet as well.
A moon doesn't have to be gigantic - our minimoons can be as small as one meter across. But they are definitely orbiting us, sometimes for a year or more.
Mikael Granvik (formerly at University of Hawaii at Manoa and now at Helsinki), Jeremie Vaubaillon (Paris Observatory) and Robert Jedicke (UH Manoa) have been simulating these minimoons and determined the Earth definitely has more than one moon at any given time.
While the typical minimoon might hang around for around nine months, some might orbit for decades.
Just because they're small doesn't mean they aren't important! These little guys are made from material as old as our solar system. The problem with scooping them up (or down) is their size, and unstable orbit.
These objects don't orbit in a pretty ellipse like ‘The Moon' but instead are tugged by the Earth, the sun and the moon. Our poor minimoons are in an interplanetary tug of war, being thrown around and orbiting erratically.
According to PhysOrg.com, "In 2006, the University of Arizona's Catalina Sky Survey discovered a minimoon about the size of a car. Known by the unimaginative designation 2006 RH120, it orbited Earth for less than a year after its discovery, then resumed orbiting the Sun."
To find and track the minimoons, the researchers used a supercomputer to simulate 10 million asteroid passes, then took 18,000 of those that would be captured by our gravity and tracked their progress around the planet.
Just because the big moon is famous doesn't mean it's the only one out there; watch out for the little guys too!