The new moon, 2020 CD3, captured by the Gemini North telescope on Hawaii’s Maunakea The international Gemini Observatory/NSF’s National Optical-Infrared Astronomy Research Laboratory/AURA/G. Fedorets

Earth might have a tiny new moon. On 19 February, astronomers at the Catalina Sky Survey in Arizona spotted a dim object moving quickly across the sky. Over the next few days, researchers at six more observatories around the world watched the object, designated 2020 CD3, and calculated its orbit, confirming that it has been gravitationally bound to Earth for about three years.

An announcement posted by the Minor Planet Center, which monitors small bodies in space, states that “no link to a known artificial object has been found”, implying that it is most likely an asteroid caught by Earth’s gravity as it passed by.

BIG NEWS (thread 1/3). Earth has a new temporarily captured object/Possible mini-moon called 2020 CD3. On the night of Feb. 15, my Catalina Sky Survey teammate Teddy Pruyne and I found a 20th magnitude object. Here are the discovery images. pic.twitter.com/zLkXyGAkZl Advertisement — Kacper Wierzchos (@WierzchosKacper) February 26, 2020

This is just the second asteroid known to have been captured by our planet as a mini-moon – the first, 2006 RH120, hung around between September 2006 and June 2007 before escaping.

Our new moon is probably between 1.9 and 3.5 metres across, or roughly the size of a car, making it no match for Earth’s primary moon. It circles our planet about once every 47 days on a wide, oval-shaped orbit that mostly swoops far outside the larger moon’s path.

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The orbit isn’t stable, so eventually 2020 CD3 will be flung away from Earth. “It is heading away from the Earth-moon system as we speak,” says Grigori Fedorets at Queen’s University Belfast in the UK, and it looks likely it will escape in April.

However, there are several different simulations of its trajectory and they don’t all agree – we will need more observations to accurately predict the fate of our mini-moon and even to confirm that it is definitely a temporary moon and not a piece of artificial space debris. “Our international team is continuously working to constrain a better solution,” says Fedorets.

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