Mysterious near-Earth asteroid turns out to be a piece of the Moon

Asteroid 2024 PT5, which came close to Earth last year, was likely ejected into space from the moon’s surface in a collision thousands of years ago. Now it can help us learn about how our moon is linked to space rocks.

Asteroid 2024 PT5. Source: phys.org

Mysterious guest

A small near-Earth object, 2024 PT5, caught the world’s attention last year after a telescope found it had been close to our planet for several months but not orbiting it. The asteroid is about 10 meters wide and poses no threat to Earth, but its orbit around the Sun closely matches the orbit of our planet, hinting that it may have originated somewhere nearby.

As described in a study published in Astrophysical Journal Letters, scientists have gathered additional evidence that 2024 PT5 is of local origin: it appears to be composed of rock that broke away from the moon’s surface and was ejected into space after a violent impact.

Asteroid detection

“We had a general idea that this asteroid may have come from the moon, but the smoking gun was when we found out that it was rich in silicate minerals—not the kind that are seen on asteroids but those that have been found in lunar rock samples,” said Teddy Kareta, an astronomer at the Lowell Observatory in Arizona who led the study.

“It looks like it hasn’t been in space for very long, maybe just a few thousand years or so, as there’s a lack of space weathering that would have caused its spectrum to redden.”

The asteroid was first detected on August 7, 2024, by a telescope in Sutherland, South Africa, part of the University of Hawaii’s Asteroid Terrestrial-impact Last Alert System (ATLAS). Kareta’s team then used observations from the Lowell Discovery Telescope and NASA’s Infrared Telescope Facility (IRTF) at the Mauna Kea Observatory in Hawaii to reveal that the spectrum of reflected sunlight from the surface of the small object did not match the spectrum of any known type of asteroid; instead, the reflected light was more consistent with lunar rock.

Object 2024 PT5 and space debris

The second clue appeared while observing the movement of the object. Along with asteroids, space age debris such as old rockets from historic launches can also be found in Earth-like orbits.

The difference in their orbits relates to how each type responds to the pressure of solar radiation, which arises from the pulse of photons – quantum particles of light from the Sun that exert a tiny force when they collide with a solid object in space. This exchange of momentum from many photons over time can nudge the object slightly, speeding up or slowing it down. While a man-made object, such as a hollow rocket booster, will move like an empty tin can in the wind, a natural object such as an asteroid experiences much less impact.

To exclude that 2024 PT5 is space debris, scientists at NASA’s Center for Near-Earth Object Studies (CNEOS), led by the agency’s Jet Propulsion Laboratory in Southern California, analyzed its motion. Accurate calculations of the object’s motion under gravity allowed them to find additional motion caused by solar radiation pressure. It appeared that these effects were too small for the object to be artificial, proving that 2024 PT5 is most likely of natural origin.

Asteroid and lunar studies

The discovery of 2024 PT5 doubles the number of known asteroids thought to originate from the Moon. Asteroid 469219 Kamo’oalewa was found in 2016 with an Earth-like orbit around the Sun, indicating that it could also have been ejected from the Moon’s surface after a strong impact. Since telescopes become more sensitive to smaller asteroids, more potential lunar boulders will be detected, creating an exciting opportunity not only for scientists studying the rare asteroid population, but also for scientists studying the Moon.

While a lunar asteroid may be directly related to a particular impact crater on the Moon, its study may provide insight into cratering processes on the mottled lunar surface. In addition, material from deep beneath the lunar surface — in the form of asteroids passing close to Earth — may be available for future scientists to study.

According to phys.org

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