Earth gains a new mini-moon: Asteroid 2024 PT5 joins the orbit

From September 29 to November 25, Earth will have two natural satellites. In addition to the Moon, asteroid 2024 PT5, also known as the mini-moon, will orbit the Earth.

Asteroid 2024 PT5 was identified on August 7 of this year using the ATLAS (Asteroid Terrestrial-impact Last Alert System). This is a tool that detects potentially Earth-threatening asteroids. The object is about 10 metres in diameter, which makes it too small and not bright enough to observe with the naked eye or even through amateur telescopes.

Professors Carlos de la Fuente Marcos and Raúl de la Fuente Marcos from the Complutense University of Madrid published their research findings in The Research Notes of the AAS. They reported that Earth can regularly capture asteroids from near-Earth objects (NEO) and pull them into orbit, creating mini-moons. They stated that the shape of asteroid 2024 PT5 was discovered during routine monitoring of newly identified objects.

How can Earth capture an asteroid and turn it into a mini-moon? This is not a very common phenomenon, although quite a few asteroids fly close to our planet, sometimes even at distances shorter than the distance to the Moon. Usually, they pass Earth without becoming moons, continuing their journey on their orbit, explained Damian Jabłeka, deputy director of the Silesian Planetarium.

He added that even the smallest celestial bodies can be considered natural satellites if they get into Earth's orbit and stay there for a while. For this to be possible, certain conditions must be met.

Sometimes, the combination of the distance, direction of flight, and speed of such a small celestial body causes it to be captured by the gravitational pull of our planet and start orbiting. All objects, including artificial satellites that we send into space, must have an appropriate speed to maintain their orbit, not fall to Earth, or fly off into space. It is quite a coincidence for a celestial body to find itself at the right distance from Earth, moving at the right speed and in the right direction emphasized Damian Jabłeka.

Prof. Carlos de la Fuente Marcos from the Complutense University of Madrid, quoted by Space.com, explained that to become a mini-moon, an approaching body must get to a distance of about 2.8 million kilometres from Earth and move "slowly," at a speed of about 2,200 kilometres per hour.

Damian Jabłeka noted that so far, no asteroid has started orbiting Earth permanently, "because the presence of the Moon and the Sun causes them to fly off into space after a few orbits."

The expert added that the celestial bodies that have been on Earth's orbit for longer have so far been two objects: asteroid 2006 RH120, which was the second moon of Earth from July 2006 for almost a year, and 2020 CD3, which - according to researchers - orbited our planet for up to three years. There are also examples of short-term captures, such as: 1991 VG and 2022 NX1, which as a mini-moon will likely return in 2051.

After leaving Earth's orbit, asteroid 2024 PT5 will be closest to Earth on January 9, 2025, and then leave the vicinity of the planet to return to the asteroid belt. It will reappear near Earth only in 2055.