Earth had a brief mini-moon that was a piece of the true moon

An enormous rock orbiting close to Earth seems to have originated from the moon, the second such object recognized to exist, with perhaps greater than a dozen awaiting discovery.

The asteroid, known as 2024 PT5, is about 10 metres vast. Noticed in August, it was later snared by Earth’s gravitational pull, turning into a second moon of our planet, known as a mini-moon, between September and November.

Re-examining the asteroid, Teddy Kareta at Lowell Observatory in Arizona and his colleagues have discovered that its look doesn’t match that of most different recognized asteroids. Nevertheless, mild mirrored by the asteroid to infer its composition – wealthy in pyroxene however low in olivine – revealed that it does match samples from the moon collected by the Apollo 14 mission in 1971.

“Apollo 14 primarily sampled the lunar highlands,” says Kareta, the lighter parts of the moon that we are able to see from Earth. This means one thing slammed into this area in comparatively current historical past – perhaps the previous 200,000 years – and blasted rocks into area together with 2024 PT5, he says. “So, if we had to bet which part of the moon this thing came from, it probably came from the highlands.”

This might make 2024 PT5 the second recognized asteroid to have originated from the moon, after an object known as Kamo‘oalewa was also found to have a lunar origin in 2021. Both objects are known as quasi-satellites, because they share a similar orbit to Earth, and are also red from their exposure to the sun. “It’s like rocks getting a sunburn,” says Kareta.

The existence of a second moon asteroid is “really exciting”, says Kareta. “It means there’s a bunch of these things out there. Nature doesn’t just make two of something.” Kareta predicts there are about 16 moon asteroids orbiting close to Earth, based mostly on how usually they may be produced and the way lengthy they need to keep in area.

Renu Malhotra on the College of Arizona, a part of the crew that deduced the lunar origin of Kamo‘oalewa, says that moon asteroids in all probability solely stay noticeable close to Earth for just a few million years, till their orbits are “diffused into bigger space”. Then they vanish among the many hundreds of different near-Earth asteroids. “It would be very hard to tell where they came from,” she says, as a result of they’re so small and faint.

Such lunar asteroids are unlikely to be seen too regularly as a result of they would want simply the proper situations to kind. If an impression on the moon is just too low vitality, the resultant particles would merely fall again to the lunar floor. An excessive amount of vitality, and the particles is flung into the broader photo voltaic system.

“The preferred location is the trailing hemisphere,” says Malhotra, the half of the moon pointing backwards in its orbit, which would cut back the rate of the particles and stop it leaving the Earth-moon system.

China plans to launch a mission to go to Kamo‘oalewa in 2025 known as Tianwen-2, which might give us insights on these objects. “These would be the most fresh, pristine asteroids generated in recent times,” says Malhotra. “They might contain fingerprints of their impact history.”