There's More Than One 'Moon' Orbiting Earth

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The gravitational dance between asteroid 2016 HO3, Earth and the Sun. NASA

Well, this is awkward. Earth's relationship with the moon is not a monogamous one. Scientists identified a second, mini-moon orbiting our planet in 2016 that has probably been around for about 100 years, said NASA.

This second moon looks to be a recently captured asteroid, and like a mistress, its subtle dance with Earth may be fleeting, only sticking around for a few centuries. Still, it's a remarkable event that proves just how dynamic our gravitational relationship is with near-Earth objects.

This moon isn't the only "mini-moon" orbiting Earth either. A group of international astronomers also discovered there are many natural objects in space that orbit our planet. They refer to these objects as "either temporarily captured objects (TCO) or temporarily captured flybys (TCF) depending on whether they make at least one revolution around Earth." While the astronomers use the term "mini-moons" to describe TCOs and TCFs, they said "micro-moon" is more appropriate since these objects only range between one to two meters in diameter. However, the one NASA discovered is much larger.

Getting to know our near-Earth companion

The video above from NASA showcases in detail the path of the new mini-moon's orbit as it bobs up and down like a tiny float in choppy water. As said, it's small, measuring in at only around 120 feet across and no more than 300 feet wide, which is probably why it has taken so long for scientists to spot it. (It was only just spotted in April 2016.) Its distance from Earth varies from between 38 and 100 times the distance of our planet’s primary moon.

The quasi-satellite was given the label of asteroid 2016 HO3, though surely it ought to be in line for a more charismatic title sometime soon. Scientists also assure that the space rock is no threat to our planet or to our main squeeze, 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," said Paul Chodas, manager of NASA's Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California. "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."

"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," he added.