Does Earth Have a New Moon? Kinda But Not Really
This week NASA’s Jet Propulsion Laboratory announced news of an object traveling around the Sun in an orbit that keeps it relatively close to our own planet. The object, a near-Earth asteroid (NEO) less than 300 feet (100 m) across, is designated 2016 HO3 and has in some reports been called a “new” or “mini” moon of Earth…but that’s not entirely true. More accurately 2016 HO3 is what’s known as a quasi-satellite, and is in a temporary (albeit long-lived by human standards) orbit that takes it on a “leapfrog” path around Earth, never getting closer than 38 times the distance to the Moon—about 9.1 million miles.
So while our planet shapes and sort of shepherds the orbit of NEO 2016 HO3, it’s not a true satellite.
“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.”
Asteroid 2016 HO3 was first spotted on April 27, 2016, by the Pan-STARRS 1 asteroid survey telescope on Haleakala in Hawaii. It’s likely been traveling around the Sun alongside us for much of the 20th century, and will be sticking around for a while before it eventually heads off on its own again.
“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.”
Watch a video of how this object moves in its looping orbit over the course of an Earth year.
2016 HO3 isn’t the first such object to partner with Earth for an extended orbital dance; the 65-foot (20-meter) 2003 YN107 mentioned above entered a corkscrew orbit around our planet in 1999 before departing a few years ago (it will return again in about 50 years) and the 1,000-foot-wide 2010 TK7 is currently in a tall looping orbit around Earth-Sun L4, a Lagrange point that lies 60º ahead of Earth in its orbit around the Sun. TK7 is really an Earth trojan rather than a moon or satellite, and never gets closer than about 24 million miles.
Like YN107 and TK7, 2016 HO3 is only a temporary visitor. But it’s nice to know we have some friends out there along for the ride.