Earth gained a new moon, but it won’t stay long

For the next couple months, Earth will have a temporary “mini-moon.” Known as asteroid 2024 PT5, this small celestial body is approximately 33 feet (10 meters) in diameter and was only detected on August 7 by the Asteroid Terrestrial-impact Last Alert System in South Africa. It was captured by Earth’s gravity September 29 and is expected to remain bound to the Earth-Moon system until November 25 before continuing on its heliocentric trajectory.

Mini-moons occur when small near-Earth objects – NEOs – pass close enough to Earth to become temporarily bound by the planet’s gravity. These events have been documented but remain rare. In the case of 2024 PT5, it will not complete a full orbit around Earth, which classifies it as a “temporarily captured flyby.” The asteroid is expected to remain in Earth’s gravitational influence for a brief period before the Sun’s gravity reasserts control and draws it away.

2024 PT5 is part of a group of asteroids known as the Arjunas, which have orbits that are nearly identical to Earth’s. They periodically pass near the planet at slow enough velocities to be temporarily captured. Researchers note that 2024 PT5 will follow a trajectory similar to the asteroid 2022 NX1, which was captured twice by Earth’s gravity in 1981 and 2022.

The asteroid’s small size and faint brightness are likely to make it undetectable by casual observers. Professional astronomers may attempt to observe it using telescopes with at least a 30-inch (76-centimeter) diameter and equipped with advanced detectors such as CCD or CMOS sensors. These instruments are required due to the low brightness of 2024 PT5, which would be invisible to standard amateur telescopes. 

After completing its temporary flyby, 2024 PT5 is expected to return to its solar orbit, with another close approach anticipated on January 9, 2025. Following that, the asteroid will leave Earth’s vicinity until its next predicted return in 2055. 

Events like the capture of 2024 PT5 are considered important for scientific study because they allow researchers to observe the gravitational influences of Earth on small celestial bodies. Observations may contribute to a better understanding of how such objects behave when temporarily captured. Studies of NEOs like 2024 PT5 are also considered valuable for improving predictive models used in tracking potentially hazardous objects.

The temporary capture of asteroids has been studied for its implications in planetary defense, with researchers seeking to understand the potential risks of future NEOs. 2024 PT5 poses no danger to Earth, but its brief stay may offer scientists an opportunity to refine tracking methods and study the behavior of similar objects that pass close to the planet. 

Over the next several months, 2024 PT5 is expected to be monitored by astronomers to collect data on the object’s size, composition, and trajectory. Such observations are expected to improve the understanding of these temporary mini-moon events, which occur periodically but are difficult to observe due to their short duration and the faintness of the objects involved.