Earth mini-moon 2024: Asteroid to enter Earth's orbit for two months - will it be visible and what is it?

The ‘mini-moon’, called 2024 PT5, should arrive on 29 September and is expected to befriend the regular moon for around two months. "A mini-moon is a small object orbiting another solar system body," said Daniel Brown, an associate professor in astronomy at Nottingham Trent University.

It can either be made of rock, which is an asteroid or a mixture of rock, dust and ice, which is a comet. "In either case, we have to think about these not orbiting around us forever but for a short amount of time," said Dr Brown.

2024 PT5 was first discovered in August last year, the day before it approached Earth at a distance of 353,200 miles (568,500km). It belongs to the Arjuna asteroid belt, a group of space rocks in the solar system that revolve around the Sun.

Dr Brown said the mini-moon will orbit Earth for 57 days before eventually swinging out of the planet's gravitational pull. "There is nothing explosive or dramatic happening to it for it to leave, it simply has too much energy to hang around us for too long," he said.

Scientists predict it will re-enter our orbit in 2055. It is not the first time Earth has had a ‘mini-moon’. Four years ago, scientists identified another mini-moon called 2020 CD3, which orbited the Earth for more than a year.

Will the mini-moon be visible to see?

Sadly spectators are unlikely to see the asteroid joining Earth's orbit. Its size, which is estimated to only be around 10m wide, will be too small for the human eye or even a small telescope to witness.

Professor Carlos de la Fuente Marcos told Space.com: "The object is too small and dim for typical amateur telescopes and binoculars. However, the object is well within the brightness range of typical telescopes used by professional astronomers."