NASA has announced a new asteroid, designated 2016 HO3, that is Earth’s constant companion. It was first spotted in April of this year. This asteroid revolves around both the Earth and the sun, in a sort of spiral pattern, keeping a constant distance from us. It’s a lot further out from us than the moon is, which is why we hadn’t seen it before. It’s also rather small.
"Since 2016 HO3 loops around our planet, but never ventures very far away as we both go around the sun, we refer to it as a quasi-satellite of Earth," said Paul Chodas, manager of NASA's Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California. "One other asteroid -- 2003 YN107 -- followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity. This new asteroid is much more locked onto us. Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth's companion for centuries to come."
The asteroid’s orbital pattern is a bit eccentric, which you can see in a video at the NASA story. They compared it to a game of leap frog around the sun. You have to wonder why an asteroid just takes up with a planet for a few centuries and then moves on… maybe it’s keeping an eye on us at a distance, to see if we’re worth invading. -via Metafilter
(Image credit: NASA/JPL-Caltech)