to the moons

Scientists may have just discovered the Moon's large adult son

A new study examines Kamo`oalewa, one of Earth's quasi-satellites.

Benjamin Sharkey, a PhD student at the University of Arizona, began looking at a small, nearby space rock named Kamo'oalewa in 2017. At visible wavelengths, Kamo'oalewa was your average near-Earth asteroid. But once Sharkey began observing it in infrared light, things started to get weird.

“So when we were observing at visible wavelengths ... we're sort of saying, okay, this is an asteroid that we've kind of seen before,” Sharkey tells Inverse. “As we kept looking in the infrared, that was the process where we went, ‘Hold on, this is doing something weird.’”

Kamo'oalewa had similar light spectra to those of samples of the Moon brought to Earth by the Apollo mission. This suggests that the asteroid may have once been a part of Earth’s Moon, and was later ejected by an ancient impact.

The findings are detailed in a study published in the journal Nature.

What is a quasi-satellite?

A quasi-satellite is a space rock that follows the Earth in a similar orbit around the Sun, staying close to the planet without actually orbiting it. Earth has five quasi-satellites, including Kamo'oalewa (the name is derived from the Hawaiian words ka or “the,” and moʻo or “fragment”.)

Kamo'oalewa was discovered in 2016 by Hawaii’s Pan-STARRS 1 asteroid-hunting telescope. The asteroid is about 165 feet long, and gets as close as about 9 million miles away from Earth (that’s approximately 38 times further away than the Moon is to Earth).

Was Kamo`oalewa violently ejected from the Moon?

Juan A. Sanchez/PSI.

“If you're looking at it from the perspective of Earth, it looks like it's looping around the Earth but it's not exactly doing that,” Sharkey says. “But it's orbiting the Sun in a way that is so similar to the Earth that it is staying very close to where the Earth is.”

Scientists believe Kamo’oalewa has been accompanying Earth on its orbit around the Sun for the past 100 years.

Due to its small size, the asteroid has been shrouded in mystery since its discovery. But the recent study sheds light on its origins.

WHAT’S NEW —Vishnu Reddy, an associate professor in cosmochemistry and planetary astronomy at the University of Arizona, and his student Sharkey used the Large Binocular Telescope (LBT) to gaze up at Kamo’oalewa.

LBT has two gigantic mirrors, each measuring at roughly 28 feet. This allowed the scientists to get a closer look at Kamo’oalewa than ever before.

Kamo’oalewa’s orbit around the Sun allowed them to make periodical observations of the asteroid, learning more about it every time. The team began initial observations in 2017, then again in 2019, and made a final round of observations in the spring of 2021.

“So [we had] sort of three stages of looking at the data and going, hold on, let's keep looking at it,” Sharkey says.

In order to find out what the asteroid is made of, the researchers analyzed the sunlight being reflected off the surface of Kamo’oalewa. They found that the spectral characteristics of the asteroid are consistent with silicate minerals, or rocky material that has been affected by space weathering events such as micrometeorite bombardment and solar wind particles.

That same effect is consistent with samples of the Moon.

“There's an asteroid that looks pretty similar to the Moon, and is hanging out nearby to the Earth and the Moon,” Sharkey says. “So you start to say, is this a part of the process of how material moves from one thing to the other?”

By looking at the Moon, scientists have discovered several impact craters that were carved out by space objects crashing into the Moon. Hundreds of lunar meteorites have also fallen onto Earth, meaning that material frequently gets ejected from the Moon.

After closely observing Kamo’oalewa, scientists believe that the nearby asteroid may have once been a part of the Moon before getting sliced off and eventually finding its own orbit in space.

“There’s so many different groups of asteroids in the Solar System,” Sharkey says. “I think what's really cool about this one is the fact that this is such a rarely studied type of asteroid — quasi satellites.”

“Whenever you're able to study a new population, that really tells you a lot about how they're all related and you can come up with different theories of how asteroids have moved around throughout the history of the Solar System,” he adds.

WHAT’S NEXT — Scientists will get to learn even more about Kamo’oalewa soon.

The China National Space Administration (CNSA) is planning a sample return mission to Kamo’oalewa, which is set to launch in the year 2025. It could uncover if its origins can be traced to the Moon — or if something entirely different is afoot. The paper hypothesizes that it could also be an asteroid captured into a quasi-satellite origin or from a population of “Trojan” asteroids that trail the Earth.

“With spacecraft study, you can actually really say definitively what the origins could be,” Sharkey says.

Abstract: Little is known about Earth quasi-satellites, a class of near-Earth small solar system bodies that orbit the sun but remain close to the Earth, because they are faint and difficult to observe. Here we use the Large Binocular Telescope (LBT) and the Lowell Discovery Telescope (LDT) to conduct a comprehensive physical characterization of quasi-satellite (469219) Kamoʻoalewa and assess its affinity with other groups of near-Earth objects. We find that (469219) Kamoʻoalewa rotates with a period of 28.3 (+1.8/−1.3) minutes and displays a reddened reflectance spectrum from 0.4–2.2 microns. This spectrum is indicative of a silicate-based composition, but with reddening beyond what is typically seen amongst asteroids in the inner solar system. We compare the spectrum to those of several material analogs and conclude that the best match is with lunar-like silicates. This interpretation implies extensive space weathering and raises the prospect that Kamo’oalewa could comprise lunar material.
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