Asteroid will soon enter Earth’s orbit as a temporary “mini moon”

Earth will soon host a “mini-moon.”

Two astronomers in Spain who reported the discovery say an asteroid will fly past Earth next week and then orbit the planet for about two months while temporarily captured by Earth's gravity.

The asteroid, designated 2024 PT5, is 10 meters long – about the length of a standard school bus. The space rock poses no threat to Earth and is not expected to stay there for long before swinging back out into space on an orbit around the Sun.

“It will not complete an orbit around Earth, 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 remain there until November 25, just over 56 days, Marcos said.

It doesn't happen every day that Earth gets a new companion, but such mini-moon events are not entirely unusual.

Astronomers in Arizona discovered another mini-moon in Earth's orbit in February 2020 – a tiny asteroid called 2020 CD3. Its diameter was estimated to be between 1.8 and 3.3 meters, and it orbited the Earth for more than a year before being ejected back into space.

Later 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.

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

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

“A short mini-moon episode can last hours, days, weeks, or a few months, and the affected object does not even complete one orbit of 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 orbits of the Earth.”

The upcoming visit of asteroid 2024 PT5 will be brief.

The space chunk will be too small and faint to be seen with conventional 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 more about the asteroid's surface composition and its rotation rate, he said. These observations could help researchers figure out its origin, which in turn could shed light on other asteroids, including ones that could be dangerous to Earth.

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