An illustration of the temporary mini-moon 2024 PT5 around Earth, with the moon in the distance. (Image credit: Robert Lea (created with Canva))

Earth almost always has more than one moon. The others are just very small, and they never stay long — but they could provide accessible and unique insights into the solar system.

Temporary satellites, or mini-moons , are small asteroids that wander into Earth’s neighborhood and get captured briefly by our planet’s gravity. A typical one stays about nine months and circles Earth roughly three times before escaping back into orbit around the sun , Grigori Fedorets of Finland's University of Helsinki said in a presentation at the Europlanet Science Congress (EPSC) 2026 in The Hague in September.

Fedorets' modeling suggests that the largest mini-moon around Earth at any given moment is typically only about 75 centimeters (30 inches) across. An asteroid about 3 meters (10 feet) wide should be captured every 10 to 20 years.

"This is not just a theoretical construct.…