Asteroid will soon enter Earth's orbit as a temporary “mini-moon.”

Earth is expected to host a visiting “mini-moon.”

An asteroid is expected to fly past Earth next week and then orbit the planet for about two months while temporarily captured by Earth's gravity, according to two astronomers in Spain who reported the discovery.

The asteroid, named 2024 PT5, is 33 feet long — about the size of a regular school bus. The space rock poses no threat to Earth and is not expected to remain there long before swinging back into space on an orbit around the sun.

“It will not complete a single orbit around Earth, but only a portion of it,” said Carlos de la Fuente Marcos, co-author of a study on the asteroid published this month in the American Astronomical Society's journal Research Notes.

The asteroid is expected to enter Earth's orbit on Sunday and will lurk there until Nov. 25, just over 56 days, Marcos said.

It's not every day that Earth adopts a new companion, but such mini-lunar events are not uncommon either.

Astronomers in Arizona discovered another minimoon visiting Earth – a tiny asteroid called 2020 CD3 – in Earth's orbit in February 2020. It was estimated to have been 6 to 11 feet in diameter and orbited the Earth for more than a year before being ejected back into space.

Subsequent studies found that asteroid 2020 CD3 was most likely captured by Earth's gravity in 2017, three years before it was discovered in our backyard on the planet.

Previously, in June 2006, an asteroid called 2006 RH120, which orbits the Sun and passes close to Earth every few decades, was captured by Earth's gravity and remained until about September 2007.

Minimoons typically come in two “sizes,” Marcos said: short or long.

“A short mini-lunar episode can last hours, days, weeks or a few months, and the affected object does not complete a single orbit around the Earth,” he said in an email. “On the other hand, long mini-moon episodes last at least a year and probably longer, and the affected object completes one or more revolutions around the Earth.”

Asteroid 2024 PT5's upcoming visit will be brief.

The space rock will be too small and faint to be seen with normal telescopes and binoculars. Marcos said he and his colleagues plan to study it using the Gran Telescopio Canarias, a ground-based observatory in the Canary Islands.

Scientists hope to learn something about the asteroid's surface composition and its rotation speed, he said. These observations could help researchers figure out its origin, which in turn could shed light on other asteroids, including those that could be dangerous to Earth.

An asteroid early warning system called ATLAS (short for Asteroid Terrestrial-Impact Last Alert System) discovered PT5 in early August 2024. The ATLAS telescopes were funded by NASA and developed by the University of Hawaii.