Somewhere along the way our planet picked up a stray. Like a lost puppy, a tiny asteroid has been tagging along in Earth’s orbit for at least a century—and it'll probably follow along for at least a few hundred years more. Officially known as 2016 HO3 the space rock has faithfully dogged at Earth's heels as the planet makes its way around the sun.
Scientists at the Pan-STARRS 1 telescope on Haleakala, Hawaii spotted the little asteroid back on April 27. While it might seem curious that the rock could orbit with Earth under the radar, there are two main reasons it has gone unnoticed for so long, Mike Wall reports for Space.com.
First, it really is little: Scientists estimate that the asteroid is only about 130 to 330 feet wide, making it a tiny speck in the vastness of space. Second, its orbit takes it so far away from the Earth that 2016 HO3 is only considered a “quasi-satellite,” as opposed to the moon.
"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," Paul Chodas, manager of NASA's Center for Near-Earth Object Studies, says in a statement. "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."
The astronomers that detected the asteroid were keeping a lookout for rogue rocks that potentially pose a threat. But there’s no danger of the tagalong crashing into the planet. Its looping orbit is far enough from Earth that if it does eventually break free in a few hundred years, it will most likely drift back off into space, Brad Plumer writes for Vox. Even at its closest point, 2016 HO3 is at least about 9 million miles away.
"One other asteroid—2003 YN107—followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity,” Chodas says. “This new asteroid is much more locked onto us.”
However, that doesn’t meant that there aren’t more dangerous ones out there. A NASA audit in 2014 found that researchers only know about 10 percent of the near-Earth objects more than a few hundred feet wide floating around in space, Plumer writes.
For now, the space agency is working to improve its asteroid detection abilities, as well as devising ways to deflect any dangerous ones that may be heading our way. Luckily, 2016 HO3 seems friendly enough.