An asteroid near Earth could become a temporary moon, then a crash risk
Scientists have spotted a small asteroid that may circle Earth as a mini moon before shifting onto a path that could make it a hazard later in the century.
The asteroid, known as 2022 RD2, belongs to a rare class of space rocks called Arjunas. These objects travel around the sun on orbits that closely match Earth’s and sometimes drift near the planet at unusually low speeds. That sluggish pace can allow Earth’s gravity to trap them for a short time, creating what researchers call mini moons.
NASA has calculated the asteroid’s orbit and placed it on its risk list for potential impacts, though the agency’s Center for Near-Earth Object Studies has reached somewhat different conclusions about the asteroid's future trajectory.
If these predictions hold, 2022 RD2 could become one of the few known asteroids to shift from near-Earth object to temporary moon and later to a potential crash risk — all within a single lifetime.
A team of astronomers in Madrid says 2022 RD2 follows an especially unstable path. It has a Lyapunov time — a measure of how quickly an orbit becomes unpredictable — of less than 20 years, much shorter than that of most near-Earth asteroids. That rapid change means small gravitational nudges can push the rock onto dramatically different routes over just a few decades.
Their findings appeared this week in Research Notes of the American Astronomical Society. The paper’s authors, brothers Carlos and Raúl de la Fuente Marcos of the Universidad Complutense de Madrid, have previously reported on the "quasi-moon" 2025 PN7 and the mini-moon 2024 PT5, which briefly orbited Earth last year.
A key distinction, they note, is that mini moons get briefly captured by Earth’s gravity. But 2025 PN7 is more of a stalker, merely following Earth on its travels around the sun without becoming a true satellite.
The Arjunas interest researchers because of their scientific and practical potential, Carlos told Mashable.
"On the one hand, they are easier to access than other asteroids, so they can be used to test space technology or even to attempt commercial ventures on them such as mining," he said. "On the other hand, some of them are suspected lunar debris resulting from present-day impacts on the moon."
Simulations suggest 2022 RD2 could slip into a temporary orbit around Earth between 2043 and 2044, becoming a mini moon for several months. The team applied standard criteria for temporary captures: a close approach, a reduction in relative speed, and a period during which Earth’s gravity exerts enough control to form a true orbit.
After 2022 RD2 leaves Earth’s neighborhood, its path appears to grow more erratic. Some possible trajectories include collision paths beginning around 2080, according to the paper.
But NASA’s models put potential impact dates even later and estimate the odds at less than 0.1 percent, said Davide Farnocchia, a navigation engineer with the center. The asteroid is also relatively small, perhaps the size of a three-story building.
"So it wouldn't cause any significant damage even in the unlikely case it were on an impact trajectory," Farnocchia told Mashable.
Many recent mini moons and quasi-moons appear to belong to the Arjuna population — a loose cluster of Earth-like objects that trail our planet along its path around the sun. Their origins and composition remain largely unknown because only a few have been studied in detail. Some show similarities to the actual moon, Carlos said, but scientists need more data.
Although some small objects near Earth turn out to be old spacecraft or rocket boosters, the researchers say 2022 RD2 is almost certainly natural. And while their projections don't confirm a future collision, they can't yet rule it out.
"The study of this population is just beginning," Carlos said. "Paradoxically, being so close to us, they are comparatively difficult to study, as many of them have short visibility windows and far between."
