Rubin telescope should find more of Earth's mysterious 'mini-moons' — including some we can study up close

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...