The Asteroid That Shadows the Earth

The Earth has a newly discovered neighbor in the form of a "quasi-moon" that appears to be following us around through space.

The newly discovered object, named 2023 FW13, is an asteroid measuring around 50 feet in diameter that orbits the sun at around the same rate as the Earth, and circles around our planet in a sweeping oval-shaped object as it does so.

Its looping orbit around the Earth makes it a quasi-moon or quasi-satellite, of which there are only a few others.

"It seems to be the longest quasi-satellite of Earth known to date," Adrien Coffinet, an astronomer and journalist who first categorized the asteroid as a quasi-moon after modeling its orbit, told Sky & Telescope.

Strangely, these objects are rarely orbiting the Earth due to the gravitational pull of our planet: rather, the quasi-moons are in resonance with the Earth, merely orbiting the sun at the same rate and location as the Earth.

"The dimension of the loop (about .18 astronomical unit in radius [around 16,700,000 miles] is so large that Earth plays essentially no role in its motion," Alan Harris, a research astronomer at the Space Science Institute, told Sky & Telescope. "[It's] in no way associated with Earth other than by chance."

These asteroids usually only stay in orbit around the Earth for a few decades, before flinging back off to orbit the sun solo. 2023 FW13, on the other hand, appears to have been orbiting the Earth since at least 100 BC, which would make it the most stable quasi-satellite of Earth ever found.

This quasi-moon asteroid is also expected to continue to follow this orbital path until around A.D. 3700. It was first observed on March 28th by the PanSTARRS observatory on Maui, Hawai'i, and was officially announced on April 1st after further observations from other observatories, Minor Planet Center (MPC) reported. MPC is the single worldwide location for receipt and distribution of positional measurements of minor planets, comets and outer irregular natural satellites of the major planets.

The Earth also has another quasi-moon named Kamo'oalewa, or 2016 HO3, which was discovered in 2016. This object is thought to have orbited the Earth for almost a century and is expected to remain in orbit for at least 300 more years, according to Jet Propulsion Laboratory, a research and development lab federally funded by NASA and managed by Caltech. One 2021 study published in the journal Communications Earth & Environment suggested that this asteroid could actually be a fragment of Earth's moon.

Luckily for us, these asteroids are some of the least likely to hit our planet, due to their resonant orbits.

"The good news is, such an orbit doesn't result in an impacting trajectory 'out of the blue,'" Harris said. "Such an orbit has greater long-term stability than other non-resonant orbits."

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