Earth has a new 'quasi-moon' after discovery of newfound asteroid 2023 FW13

The newfound space rock 2023 FW13 has an orbit that keeps it as a constant companion of Earth, like that of 2016 HO3, which is shown here.
The newfound space rock 2023 FW13 has an orbit that keeps it as a constant companion of Earth, like that of 2016 HO3, which is shown here. (Image credit: NASA/JPL-Caltech)

Astronomers have discovered yet another ancient cosmic companion of Earth.

The newfound asteroid 2023 FW13 circles the sun in sync with Earth, making it our planet's "quasi-moon." The space rock is in an orbit so elaborate that "it sweeps out halfway to Mars and in halfway to Venus," Sky & Telescope's David Chandler reported Friday (April 7).

The asteroid was first spotted on March 28 by scientists using the Pan-STARRS survey telescope, which snaps pictures of the night sky from its perch atop Haleakala, a dormant volcano on the Hawaiian Island of Maui.

Related: Photos of asteroids in deep space

The space rock's presence was soon confirmed using the Canada-France-Hawaii Telescope in Hawaii and the Kitt Peak National Observatory and Mt. Lemmon SkyCenter in Arizona. After passing all checks, its discovery was officially announced on April 1.

The news caught the attention of Adrien Coffinet, a journalist at the French news website Futura - Inspirons l'avenir. By chalking out the asteroid's path using an orbit simulator developed by amateur astronomer Tony Dunn, Coffinet was the first to find that 2023 FW13 travels around the sun in the same amount of time that Earth does, while also looping around our planet. These details led him to conclude that the space rock is likely a quasi-moon or quasi-satellite of Earth.

While 2023 FW13 — which could be about 65 feet (20 meters) wide, according to early estimates — tags along with Earth, astronomers say the sun has significantly more influence on the space rock. Earth disturbs the asteroid's orbit only slightly, in such a way that it always hovers in the planet's vicinity, Coffinet reported Thursday (April 6). Each year, the space rock ventures within 9 million miles (15 million kilometers) of Earth. For reference, at the closest point in its slightly elliptical orbit around Earth, the moon comes within about 223,693 miles (360,000 km) of our planet.

2023 FW13 is not the first object of its kind discovered in Earth's cosmic neighborhood. Astronomers think the space rock's orbit is similar to that of that asteroid Kamo'oalewa, also known as 2016 HO3, another Earth quasi-satellite spotted in 2016 that never drifts too far from the planet.

Since 2023 FW13's discovery, citizen astronomers scouring archival data have found sightings of the asteroid since 2012. Using all that data, they calculated past and future orbits of the space rock, and think it has been in our general neighborhood since 100 B.C. and will stay until at least A.D. 3700, according to Sky & Telescope's David Chandler. "If that's correct, 2023 FW13 would be the most stable quasi-satellite of Earth ever found," Chandler writes.

Like Kamo'oalewa, astronomers think 2023 FW13 does not pose a threat to Earth.

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Sharmila Kuthunur contributor

Sharmila Kuthunur is a Seattle-based science journalist covering astronomy, astrophysics and space exploration. Follow her on X @skuthunur.