When you look up into the night sky, you can almost always see our celestial neighbor the moon. That rock in the sky isn’t going anywhere, but what you might not know is that from time to time we pick up hitchhikers. Astronomers have recently discovered an asteroid that is orbiting Earth acting as a sort of minimoon.
The asteroid, with the scientific — if not particularly interesting — name of 2016 HO3, was discovered back in April. The Pan-STARRS 1 survey based on Haleakala, Hawaii found the asteroid which is approximately 40 – 100 meters in size. Before anyone asks, the asteroid does not pose any risk to us here on Earth. At its closest, it will still be more than 9 million miles away from us.
2016 HO3 is a sneaky asteroid too. Though it was only discovered a few months ago, it is likely to have been following us around for at least a century. It is in such a stable orbit around our planet that it may stick around for centuries to come. Paul Chodas (NASA Jet Propulsion Laboratory) described why the asteroid is called a quasi-satellite:
Since 2016 HO3 loops around our planet, but never ventures very far away as we go around the Sun, we refer to it as a quasi-satellite of Earth. In effect, this small asteroid is caught in a little dance with Earth.
2016 HO3 might be dancing with Earth, but its orbit is more of a drunk gyration than an elegant dance. The video below explains how the asteroid’s orbit coincides with ours.
Sky and Telescope describes its orbit in more detail than I would be able to muster:
2016 HO3’s orbit takes it alternately sunward and ahead of Earth for six months at a time, before our planet’s gravity grabs it and drags it back, forcing it to play catch up. This strange motion is slightly tilted relative to the ecliptic plane, resulting in a corkscrew twist in the orbit over several decades.
You can read more about the history of Earth’s quasi-satellites, and other information about Temporary Captured Objects at the source link below.Source: Sky and Telescope
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