Earth's Temporary Mini-Moon: Asteroid 2024 PT5 to Orbit This Fall

Asteroid 2024 PT5 becomes Earth's temporary mini-moon for 56 days starting Sept 29. No impact risk. Next return 2055.

Earth to Gain a Temporary Mini-Moon

Starting September 29, Earth will briefly host a second moon. Asteroid 2024 PT5, a small space rock, will enter a temporary orbit around our planet for 56.6 days before drifting back into its solar orbit on November 25. The phenomenon was reported in the Research Notes of the American Astronomical Society.

Discovery and Characteristics

Astronomers detected 2024 PT5 on August 7 using the NASA-funded ATLAS telescope in South Africa. Led by Carlos de la Fuente Marcos of Complutense University of Madrid, the team estimates its diameter at roughly 37 feet (11 meters), with a possible range of 16 to 138 feet (5–42 meters). That makes it potentially larger than the Chelyabinsk meteor that exploded over Russia in 2013, but it poses no danger. At its closest, it will stay about 2.6 million miles (4.2 million kilometers) from Earth—roughly ten times the distance to the Moon.

How Mini-Moons Form

Mini-moons come in two types, explains de la Fuente Marcos. Long-term captures, called temporarily captured orbiters, complete multiple laps over years. Short-term captures, or temporarily captured flybys like 2024 PT5, last only days to months. Earth's last long-term mini-moon was asteroid 2020 CD3, which circled for a few years before detection. Such short-term events occur several times per decade, while long-term ones happen once every 10–20 years.

Required Conditions

For an asteroid to become a mini-moon, it must approach Earth slowly and closely: within 2.8 million miles (4.5 million kilometers) at speeds under 2,237 mph (3,600 km/h). Robert Jedicke, a solar system expert at the University of Hawaii, notes that almost all asteroids approach too fast or at the wrong angle. Only rare gravitational nudges allow a slow, well-angled asteroid to be captured.

Origin and Future Observations

2024 PT5 likely hails from the Arjuna asteroid group, whose members share Earth-like orbits. Researchers plan further study using the Gran Telescopio Canarias and Two-Meter Twin Telescope in Spain's Canary Islands, though it will be too faint for amateur telescopes. After its mini-moon phase, the asteroid will make a close approach on January 9, 2025, and may return as a mini-moon in November 2055 and early 2084, offering repeated opportunities for study.