The Earth gains a second moon, sort of
In a move that should delight astronomers and annoy astronomy teachers with smartass students, the Earth just picked up a second moon. Sort of.
NASA recently discovered the whimsically named asteroid, 2016 HO3, which is currently locked into an orbit around the sun that also keeps it within the orbital pull of Earth. It sometimes moves out far ahead of the Earth before being pulled back, then it soon trails far behind us before gravity re-exerts itself.
At its closest point from the Earth, the asteroid is around 38 times the distance of our incumbent moon ( which is roughly 238,900 miles away); at its furthest, it is around 100 times the distance. It has never been closer than nine million miles. That distance eliminates it as a true satellite of Earth, and instead makes it a “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, of 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 object is also tiny, no bigger than 100 meters. That makes its discovery on April 27, 2016 by NASA’s awesomely named Planetary Defense Coordination Office fairly incredible. That will also make getting a closer look from a spacecraft difficult (but not impossible).
The asteroid is locked in a circular orbit around the Earth, and an elliptical orbit around the sun. It will one day break away, but it poses no threat to us. It will remain in orbit around Earth for a few centuries more at least before it goes walkies.
“The asteroid’s loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth’s gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon,” said 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.”
So huzzah! Earth has a second moon! Kinda! We may never see it, but it’s there. Oh yes, it’s there.