Small asteroid spotted circling Earth

by Lucas Joel
Tuesday, September 13, 2016

Researchers recently discovered an asteroid that circles our planet as we circle the sun. Credit: Callan Bentley.

Earth has a companion other than the moon, according to scientists at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., who identified a previously unseen asteroid that circles around our planet as it follows its own orbit around the sun.

Astronomers first spotted the asteroid — estimated to be between 40 and 100 meters wide and dubbed 2016 HO3 — on April 27, 2016, using the Pan-STARRS 1 asteroid survey telescope on Haleakala, Hawaii. “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,” said Paul Chodas, manager of NASA’s Center for Near-Earth Object Studies at JPL in a press release. “Our calculations indicated 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and [that] it will continue to follow this pattern as Earth’s companion for centuries to come.”

The orbit of Earth’s tagalong takes it closer to the sun for about half the year, while for the other half the asteroid is closer to Earth. When the asteroid occasionally drifts farther from our planet, “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 [or about 38 million kilometers],” Chodas said. “The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon [about 14.6 million kilometers]. In effect, this asteroid is caught in a little dance with Earth.”

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