In a mad rush to gain hits to their sites, media outlets are at it again with headlines such as: “SURPRISE: Earth has two moons” and “Earth now has a second moon” or even “Earth has a second mini-moon, says NASA.”
So did NASA say anything about a moon? No.
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While headlines such as the ones above sound great, they are not an accurate description of the asteroid NASA astronomers discovered.
The asteroid, now named 2016 HO3, was first sighted on April 27, 2016. The Pan-STARRS 1 asteroid survey telescope, operated by the University of Hawaii’s Institute for Astronomy, made the discovery.
The object is likely to be larger than 120 feet (40 meters) but smaller than 300 feet (100 meters); however, the exact size has yet to be confirmed. 2016 HO3 is in orbit around the Sun, keeping it a constant companion of Earth. NASA researchers believe that this will be the case for centuries to come.
‘Quasi-satellite’ is not a moon
As 2016 HO3 orbits the Sun, it also circles the Earth, although it is too far away to be considered an actual satellite of our planet. However, it is the best example of a near-Earth companion, or “quasi-satellite.” Paul Chodas, manager of NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory, said in a statement:
“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.
“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.”
Asteroid 2016 HO3 spends around half of the time closer to the Sun than Earth during its yearly travel. It also passes ahead of our planet and about half of the time farther away, which causes it to fall behind.
According to NASA, its orbit is also tilted a little, causing it to bob up and then down once each year through Earth’s orbital plane. In effect, this small asteroid is caught in a game of leapfrog with Earth that will last for hundreds of years. The asteroid’s orbit undergoes a slow, back-and-forth twist over multiple decades. Chodas added:
“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.
“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.”