Earth has a companion

From the “What the…?!” files, it turns out that Earth has a newly discovered companion. No, we’re not cheating on the Moon, and it’s been hanging around for a century. But we’re just finding out about it.

On April 27, 2016, observers at the Pan-STARRS 1 asteroid survey telescope on Haleakala, Hawaii, part of the project to catalogue all near-earth objects in our solar system, discovered Asteroid 2016 HO3. It’s small—somewhere between 40 and 100 metres (120-300 feet; the exact size isn’t determined yet), and has an orbit around the sun that brings it between 38 times and 100 times the distance of the Moon—not very close, in other words.

The distance of Asteroid 2016 HO3 from Earth is why it’s not a true satellite (moon), but a near-earth companion. It’s been orbiting around the sun for about a century, and Earth’s gravity is likely to keep it doing so for centuries to come. It isn’t a threat to earth.

“In effect, this small asteroid is caught in a little dance with Earth,” according to Paul Chodas, manager of NASA's Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory. And they’ve been “dancing” like this for nearly a century, but we’ve just found it.

The reason it was found at all is because of the grossly underfunded cataloguing project of the “Planetary Defense Coordination Office” (yes, that’s a real thing). So, we know about it in large part because we realised it would be a good idea to know about asteroids in our own neighbourhood that might crash into earth one day. Serendipity, maybe.

This isn’t the first time an asteroid like this has been found, though. Another asteroid, 2003 YN107, had a similar orbit for awhile about ten years ago, then pissed off. Maybe it didn't like the dance music in our solar system. But that means there could be more that scientists just haven't found yet.

Science is fascinating, of course, and so are new discoveries. But it’s a little freaky to learn that Earth has had a companion since around World War One, and we never knew about it until around six weeks ago.

Mostly, though, it’s just fascinating.