Why Earth will temporarily get a ‘mini-moon’ in September

What is a ‘mini-moon’?

Mini-moons are asteroids that fail to escape Earth’s gravity and end up orbiting the planet for some time. They are usually very small and hard to detect — only four mini-moons of Earth have ever been discovered, and none are still orbiting Earth, according to a report by The Planetary Society.

“Some may actually have been space debris. The Gaia spacecraft was once mistaken for a minimoon, and so were rocket stages from the Chang’e 2 and Lunar Prospector missions,” the report said.

What do we know about 2024 PT5?

The asteroid was discovered with the help of the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS). It is estimated to be just 33 feet long and is too small to be visible to the naked eye or through typical amateur telescopes. However, the asteroid is within the brightness range of telescopes used by professional astronomers.

Carlos de la Fuente Marcos, professor at the Complutense University of Madrid and lead author of the study, told Space.com that 2024 PT5 has come to visit from “the Arjuna asteroid belt, a secondary asteroid belt made of space rocks that follow orbits very similar to that of Earth” at an average distance to the Sun of about 150 million kilometres.

The asteroid could possibly be a “piece of ejecta from an impact on the moon”, Paul Chodas, the director of the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory (JPL), told The New York Times. This means that 2024 PT5 could be a small fragment of the actual moon.

Some researchers suggest that chances are 2024 PT5 does not qualify as a mini-moon. An asteroid has to orbit the Earth fully at least once — 2024 PT5 will perform a horseshoe-shaped orbit. Lance Benner, the principal investigator of the asteroid radar research program at the JPL, told The NYT: “It certainly won’t complete one full revolution in the Earth-moon system this fall, so I’m not sure I would classify it as a mini-moon.”

Why is this significant?

The observations of 2024 PT5 will help scientists expand the knowledge of asteroids that pass close to the Earth and those that sometimes collide with it.

Many asteroids contain valuable minerals and water, which companies hope to extract one day and use for purposes such as rocket fuel.