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Possible new 'minimoon' discovered orbiting Earth

Tumbling through Earth's increasingly crowded orbit are about 5,000 satellites, half a million pieces of human-made debris and only one confirmed natural object: the moon (opens in new tab). Now, astronomers working out of the University of Arizona's Steward Observatory think they may have discovered a second natural satellite — or at least a temporary one. 

Meet 2020 CD3, Earth's newest possible "minimoon."

Video: Scientists track minimoon 2020 CD3 near Earth (opens in new tab)

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A minimoon, also known as a temporarily captured object, is a space rock that gets caught in Earth's orbit for several months or years before shooting off into the distant solar system again (or burning up in our planet's atmosphere). 

Related: Could the moon act as a fishing net for extraterrestrial life? (opens in new tab)

While astronomers suspect there is at least one minimoon circling Earth at any given time, these tiny satellites are rarely discovered, likely because of their relatively small size. Until now, only one confirmed minimoon has ever been detected: a 3--foot-wide (0.9 meters) asteroid called 2006 RH120, which orbited Earth for 18 months in 2006 and 2007.

Now, there may be a second. Kacper Wierzchos, a senior research specialist for the NASA and University of Arizona-funded Catalina Sky Survey, announced the discovery of a new temporarily captured object via Twitter (opens in new tab) Tuesday  (Feb. 25). The object appears to measure between 6.2 and 11.5 feet (1.9 to 3.5 m) in diameter and has a surface brightness typical of carbon-rich asteroids, Wierzchos wrote. 

According to an orbital model by amateur astrophysicist and San Francisco high school physics teacher Tony Dunn (opens in new tab), the potential minimoon has likely been trapped by Earth's gravity for about three years now and could make its exit in April 2020, resuming its regularly scheduled journey around the sun. 

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In a perfect universe, our departing minimoon would fly off and become trapped by the moon's gravity (opens in new tab), creating an even rarer class of object: a moonmoon (opens in new tab). Sadly, moonmoons remain only theoretical, and our possible new minimoon comes with some caveats of its own. 

While the object's existence has since been confirmed by several other observatories, further analysis is required to say for certain that the object is an extraterrestrial rock and not a large shard of space junk. Hopefully, we'll have an answer before April.

Originally published on Live Science.

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Brandon Specktor
LiveScience senior writer

Brandon has been a senior writer at Live Science since 2017, and was formerly a staff writer and editor at Reader's Digest magazine. His writing has appeared in The Washington Post, CBS.com, the Richard Dawkins Foundation website and other outlets. He holds a bachelor's degree in creative writing from the University of Arizona, with minors in journalism and media arts. He enjoys writing most about space, geoscience and the mysteries of the universe.