Earth’s been hiding a little secret from its partner, the moon. Turns out the Earth has had a “mini-moon” on the side for over a century, and even though the relationship has been exposed, the partnership is likely to continue for centuries to come.
The small asteroid, named 2016 HO3, was discovered on April 27 using the Pan-STARRS 1 asteroid survey telescope on Haleakala, Hawaii. What’s interesting about the asteroid is that because of its particular orbit around the sun, it’s a continuous companion to Earth. Although it is too far from us to be considered a true satellite, it is currently our best example of a near-Earth companion, or “quasi-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, in a NASA news release.
According to NASA, 2016 HO3 is at least 40 meters (120 feet) across but no larger than 100 meters (300 feet) wide, and it has likely orbited our planet for 100 years. What’s more, it is not planning on leaving anytime soon — it’s sticking around for centuries.
The asteroid has a very irregular orbit, which causes it to drift between 38 and 100 times the distance of our planet's loyal, primary moon. 2016 HO3’s orbit is also a little tilted, making it to bob up and down across Earth’s orbital plane (the flat, disk-shaped space that connects the center of the sun with the center of Earth).
Luckily, the asteroid poses no threat to Earth because it never gets closer than 14.5 million kilometers (9 million miles) to our planet.
"Earth's gravity is just strong enough to [...] hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon," explained Chodas. "The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon. In effect, this small asteroid is caught in a little dance with Earth."
Since this mini-moon is going to be hanging around for awhile, I think we should consider giving it a better name than 2016 HO3.