Astronomers Say Earth Has a Newly Discovered ‘Quasi-Moon,’ a Companion That Shares Its Orbit Around the Sun

Researchers are discussing 2025 PN7, a small celestial body that’s following a similar orbital path to our planet’s without being gravitationally tied to Earth

September 22, 2025

Sun shining light onto Earth as seen from space — Quasi-moons follow heliocentric orbits, centered around the sun, that are similar to Earth's. NASA's Johnson Space Center

Earth has a newly discovered—albeit temporary—companion in its journey around the sun.

In research published this month in Research Notes of the AAS, a non-peer reviewed publication from the American Astronomical Society that shares timely astronomical observations, scientists suggest 2025 PN7, a celestial body spotted by Hawaii’s Pan-STARRS observatory this summer, may be a quasi-satellite, also known as a quasi-moon.

“Quasi-satellites are in a resonant orbit but are not gravitationally bound to Earth, allowing for more sustained, though unbound, proximity,” the team writes in the research article. “Here, we present the newest member of this class, 2025 PN7.”

In other words, quasi-moons aren’t actually moons—they’re asteroids, as explained by the Planetary Society’s Asa Stahl last year. From our perspective, quasi-moons look like they’re orbiting Earth, but in reality, they follow a sun-centered orbit very similar to our planet’s. Mini-moons, on the other hand, are temporarily captured by Earth’s gravity, like the visiting object dubbed 2024 PT5 last year.

Astronomers have previously identified seven known quasi-moons of Earth. Among these celestial bodies, the new find would be the “smallest and the least stable,” astronomer Carlos de la Fuente Marcos, a co-author of the research from the Complutense University of Madrid, tells Live Science’s Elizabeth Howell in an email.

Amateur astronomer Adrien Coffinet was the first to point out that 2025 PN7 “seems to be a quasi-satellite of the Earth for the next 60 years,” which he posted on the Minor Planet Mailing List on August 30. After complimenting Coffinet’s find, another user added, “It has also been quasi for about the last 70 years (1955).”

“Quasi-satellites are especially interesting, because their cycling around Earth allows even very small asteroids like this one to be studied for years, and often decades, as they repeatedly come back to visit us,” amateur astronomer Sam Deen tells Sky & Telescope’s David L. Chandler.

Besides quasi-satellite motion, objects can tag along with Earth in other ways, too, according to the Planetary Society. These include Trojan orbits, which take celestial bodies in loops that are persistently ahead of or behind our planet, and horseshoe orbits, in which a body changes between being ahead and behind, keeping a greater distance than a quasi-satellite. In time, most of Earth’s known quasi-moons will start to follow Trojan or horseshoe orbits, while a number of asteroids tracing those orbits now will later turn into quasi-moons.

Fun fact: Trojan asteroids around Jupiter

Earth isn’t the only planet with Trojan asteroids. In fact, Jupiter’s Trojan asteroids form two large swarms ahead of and behind the gas giant. They will be studied by NASA’s Lucy spacecraft.

If 2025 PN7 really has been a quasi-moon for decades, why have astronomers only noted it now? Because it is small and faint, de la Fuente Marcos tells CNN’s Ashley Strickland. In fact, researchers estimate 2025 PN7 to be around 62 feet in diameter with a magnitude of about 26, meaning amateur telescopes don’t stand a chance of spotting it, per EarthSky’s Kelly Kizer Whitt.

What’s more, “currently available telescopes” can only detect the quasi-moon when it’s particularly close to Earth, as it was this summer, de la Fuente Marcos explains to CNN, so this provides few windows of opportunity for study.

Teddy Kareta, a planetary astronomer at Villanova University who was not involved in the research, tells CNN in an email that “based on what little we know so far, it’s almost certainly a rocky and natural object—sometimes old satellites and rocket junk end up in these very-near-Earth kinds of orbits, but we can often tell ‘natural’ (e.g., asteroidal) from ‘artificial’ (e.g., satellite) based on how their orbits evolve on short timescales.”

The research goes to show that even our own corner of the solar system can still have secrets in store for astronomers.

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