A small asteroid has been discovered following the Earth around the Sun. This object is too far away to be a new Moon, but it’s definitely trapped in a tug-of-war between the gravitational attraction of our planet and the Sun.
The object, named 2016 HO3, was discovered on April 27, 2016, by the Pan-STARRS 1 asteroid survey telescope on Haleakala, Hawaii. Its size has not been confirmed yet, but it’s expected to be between 40 and 100 meters (120 and 300 feet).
"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 statement.
The looping around our planet is not precise; the combination of gravitational attraction between this object, the Earth-Moon system, and the Sun changes 2016 HO3’s orbit, making it drift a little ahead or behind every year. This cosmic ballet pushes the asteroid back and forth from our planet, but never further than 100 times the distance of the Moon.
"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," added Chodas.
2016 HO3 is what we call a corkscrew asteroid, objects that are picked up from the nearby population of rocky bodies but never fully captured by Earth’s gravity. Their orbit is not very stable and they usually leave just as quickly as they come in.
"One other asteroid – 2003 YN107 – followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity," said Chodas. "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."