Starting in late September, Earth will briefly gain a new celestial companion. Unlike the familiar moon, which has orbited Earth for over 4 billion years, this newcomer — an asteroid named 2024 PT5 — will be a temporary visitor, captured by our planet’s gravity. For nearly two months, it will act as a “mini-moon,” looping around our planet before escaping back into space.

What’s a Mini-Moon?

Earth’s gravitational pull is strong, and occasionally it captures small asteroids that stray too close. These objects temporarily fall into orbit, joining our planet for a short time. 2024 PT5 will begin its journey around Earth on September 29, 2024, and by November 25, it will be flung back into the vastness of space. This marks the latest in a series of mini-moon events, which happen more often than you might think.

A team of astronomers first detected the asteroid on August 7, 2024, using NASA’s Asteroid Terrestrial-impact Last Alert System (ATLAS). This system, which includes telescopes located in Hawaii, Chile, and South Africa, is designed to spot space rocks that might pose a danger to Earth. But instead of being a threat, 2024 PT5 will merely be a transient guest in our planetary system.

The researchers led by Carlos de la Fuente Marcos, a professor at the Universidad Complutense de Madrid, explain that objects in the Arjuna asteroid belt—where 2024 PT5 originated—follow orbits similar to Earth’s. Occasionally, these objects come close enough at low speeds to be temporarily trapped by Earth’s gravity. In this case, 2024 PT5 will not complete a full orbit. Instead, it will stay within Earth’s gravitational reach for about two months, the researcher added.

A Brief but Exciting Encounter

Mini-moon events typically fall into two categories. Some asteroids become “temporary captured orbiters,” circling Earth for months or even years. NASA reported the discovery of one such mini-moon, known as 2020 CD3, in early 2020. This object, just over three meters wide, orbited Earth for about three years before breaking free. It’s very rare to spot these cosmic hitchhikers due to their small size, but advances in astronomical tools are making it easier to find them.

Others, like 2024 PT5, are “temporary captured flybys,” making brief appearances without completing an orbit. This particular mini-moon will fly close but won’t be visible to most stargazers. It is just about 10 meters in size — too small and dim to be seen without professional equipment.

In fact, Marcos notes that even the most powerful amateur telescopes won’t catch a glimpse of 2024 PT5. To observe this object, you would need a telescope with at least a 30-inch diameter and specialized detectors. However, professional astronomers plan to take advantage of the brief visit. They will conduct spectroscopic and photometric observations with their powerful tools to understand the asteroid’s composition and origin better.

Intriguingly, some scientists speculate that 2024 PT5 could be a fragment of Earth’s own moon, potentially ejected during a past collision. That would be very remarkable if confirmed, showing how objects like asteroids and debris are constantly interacting with planetary bodies.

Although only a few mini-moons have been detected so far, researchers believe there could be dozens, maybe even hundreds, waiting to be found. The discovery of Earth’s mini-moons also raises bigger questions about how often these asteroids swing by other planets. If our planet can trap small rocks, it’s likely that Mars, Venus, and of course the gas giant Jupiter have mini-moons of their own.

The latest findings appeared in the journal Research Notes of the American Astronomical Society (AAS).