The Earth stands alone in the solar system as a habitable world, as far as we know. But that doesn’t mean we don’t get visitors, most often in the form of (usually harmless) asteroids. Some even choose to stick around for a while, gaining a moonlike status.
The latest sojourning object is an asteroid that astronomers are calling 2025 PN7. Spotted this summer, it has an orbit that’s similar to Earth’s own trajectory around the sun, meaning it’s like a car traveling in the same highway lane as our planet. It’s what’s known as a quasi-moon. And of the handful of known quasi-moons, this one could be the smallest, perhaps no longer than 52 feet. (That’s shorter than a typical bowling lane.)
Some asteroids near Earth come from the main asteroid belt orbiting the sun between Mars and Jupiter. Others are chunks of the moon that have been ejected after a major meteorite impact. Because scientists have few telescopic observations of 2025 PN7, there are “no real hints about its origins, only speculations,” said Carlos de la Fuente Marcos, an astronomer at the Complutense University of Madrid and an author of a study about the quasi-moon’s discovery published this month in the journal Research Notes of the American Astronomical Society.
But one thing about the asteroid is certain: It is a temporary visitor.
2025 PN7 is part of a sparsely populated fleet of space rocks that briefly linger around, trail or lead Earth as the planet swings around the sun. And like the rest of its flock, this asteroid will eventually shoot off elsewhere into space — perhaps in about 60 years.
Earth has a number of mini-moons and quasi-moons. Mini-moons are objects that orbit our planet. But they make for fickle fans: They tend to swing around Earth for only a matter of months. One example was 2024 PT5, which joined our planet last fall and then headed its own way at the end of November.
Unlike mini-moons, quasi-moons orbit the sun, not Earth. And they are more dedicated followers than the more mercurial mini-moons: They can spend hundreds or thousands of years in lock step with Earth’s own orbit. This protracted proximity makes them good targets for planetary science missions. Another quasi-moon, Kamoʻoalewa, is the destination of Tianwen-2, a Chinese mission that aims to collect a geologic sample to bring to Earth for study.
Scientists spotted 2025 PN7 on Aug. 2 with the Pan-STARRS observatory at the University of Hawaii. The asteroid was then found in archival images going back several years, allowing astronomers to determine its precise orbit.
It seems to have shifted into its quasi-moon orbit in 1957 — just in time to witness the launch of Sputnik 1, Earth’s first artificial satellite.
The astronomers estimate that in August 1980, 2025 PN7 got as close to Earth as 2.5 million miles — about 10 times the distance between Earth and the moon. At its farthest, the quasi-moon may be about 11 million miles away.
Simulations show that it will have a 126-year residency in Earth’s orbit. In 2083, it will leave and lose its quasi-moon status.
2025 PN7’s title of tiniest quasi-moon is pending. Astronomers try to estimate an asteroid’s size based on how much sunlight its surface is reflecting. 2025 PN7 has proved difficult to observe, meaning the nature of its surface is unknown. “We cannot really tell its true size,” Dr. de la Fuente Marcos said. It might be up to 160 feet long. Additional observations, when possible, will determine whether it keeps its accolade as the tiniest of the known quasi-moons.
Either way, 2025 PN7’s newfound presence is welcome. Near-Earth asteroids — when they aren’t threatening to crash into the planet — fascinate astronomers because they offer clues about the evolution of the inner solar system.
“It is even cooler when they get captured and they stay close to the Earth for quite some time,” said Federica Spoto, an asteroid dynamics researcher at the Harvard-Smithsonian Center for Astrophysics who was not involved with the study.
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