Earth has just lost its second moon... but for how long? 🌙

For just a few months, Earth hosted a "second moon," much smaller than our faithful historical companion. This fleeting phenomenon, known as 2024 PT5, captivated astronomers before departing to continue its journey around the Sun.

An asteroid measuring 11.2 meters (about 37 feet) in diameter, 2024 PT5 approached our planet on September 29, 2024. About two months later, on November 25, it left Earth's orbit. However, this singular object hasn't bid farewell forever, promising a possible return.


Scientists, such as Carlos de la Fuente Marcos from the Complutense University of Madrid, have studied its trajectory. They found that this mini-asteroid likely originated as a fragment of the Moon, detached during an ancient impact. This origin makes it a temporary member of the Arjuna asteroid group, whose orbits, being close to Earth's, make them prone to gravitational capture.

According to Fuente Marcos, these asteroids, which approach at low speeds and come within 4.5 million kilometers (about 2.8 million miles) of Earth, can occasionally be temporarily trapped. However, such captures remain rare and short-lived.

The next visit of 2024 PT5 is scheduled for January 9, 2025. The asteroid will then pass at a distance of 1.8 million kilometers (about 1.1 million miles) from Earth, too far and too fast for another capture. Its subsequent returns in 2055 and 2084 will feature similar close approaches, with conditions unfavorable for it to become a mini-moon again.

Mini-moon captures remain rare. Over a century, only two long-term captures have been documented, compared to several short-term captures every decade. However, increased efforts to monitor near-Earth objects are raising the chances of identifying these visitors.

Fuente Marcos remains optimistic: he expects new surprises. For him, these small asteroids are furtive and regular travelers, enriching our understanding of Earth's gravitational environment.

What is an Arjuna asteroid?

Arjuna asteroids are a special class of small celestial bodies whose orbits are very similar to Earth's. They travel around the Sun at an average distance of 150 million kilometers (about 93 million miles).

These asteroids have nearly circular trajectories and low speeds relative to Earth, which makes them more likely to be temporarily captured as mini-moons. Their origin is still mysterious: some might result from ancient collisions between celestial bodies, while others could be fragments ejected from planets or moons.

Arjuna asteroids are key study subjects for better understanding gravitational interactions and the potential threats posed by near-Earth objects.