An Object from Deep Space Has Entered Earth's Orbit

The possible 'mini-moon' quietly started orbiting Earth three years ago, and was just detected by astronomers.
February 26, 2020, 5:30pm
A 'Mini-Moon' from Deep Space Has Entered Earth's Orbit
Image: Catalina Sky Survey via @WierzchosKacper

Earth has picked up a tiny asteroid hitchhiker, according to astronomical observations made this month.

Called 2020 CD3, the space rock was captured from deep space by our planet’s gravity, making it only the second temporary “mini-moon” that astronomers have spotted orbiting Earth.

The asteroid was discovered on February 15 by Theodore Pruyne and Kacper Wierzchos, a pair of astronomers based at the University of Arizona. On Tuesday, Wierzchos described the find as “a big deal” on Twitter and revealed that the object appears to have been tugged into orbit around Earth about three years ago.

The newly identified asteroid is only a few meters wide, but Pruyne and Wierzchos were able to detect it thanks to the NASA-funded Catalina Sky Survey (CSS), which is specially designed to flag and track near-Earth objects (NEOs). CSS was also the facility that spotted the first captured asteroid, called 2006 RH120, which got sucked into Earth orbit in 2006 and was ejected back out into heliocentric orbit in 2007.


“Finding 2020 CD3 was quite a surprise, and it is amazing to be able to discover such interesting objects,” Pruyne said in an email. “It is truly a statement of how monumental CSS has been to astronomy, and working for CSS is an honor.”

The International Astronomical Union’s Minor Planet Center, which manages the official catalogue of small celestial bodies, confirmed that 2020 CD3 is a temporary satellite on Tuesday.

But don’t get too attached to the new mini-moon, because current projections suggest that it will be tossed out of Earth orbit in April 2020. These predictions are based on more than 50 sightings of 2020 CD3, which scientists have used to generate possible orbits.

“Observations get reported to the Minor Planet Center,” explained amateur astronomer Tony Dunn, who has created several graphics of the object’s possible orbits using his “Gravity Simulator” software. “People then look at these orbits and favor or eliminate orbits based on what is realistic. Sometimes they discard what they feel are unreliable observations.”

Though only two of these captured asteroids have been imaged so far, there are likely more of them out there that are simply too faint and small to be detected. A 2012 study in the journal Icarus predicted that, statistically, there is at least one meter-scale asteroid orbiting Earth at any particular time.

For more than a century, skywatchers have claimed to have spotted these temporary satellites but CSS is the only facility so far that has captured definitive observations of them. The introduction of next-generation telescopes, such as the Vera C. Rubin Observatory in Chile, will likely lead to many more detections of these orbital stowaways.

Update: This article has been updated to include comments from Theodore Pruyne and Tony Dunn.