The mysterious object known as Kamoʻoalewa appears to be a wandering fragment of the moon, the researchers report online November 11 on Communications Earth & Environment.
The violent history of the moon is written on his face. Over the course of billions of years, space rocks have perforated craters on its surface, expelling debris. Now, for the first time, astronomers may have spotted the rubble of one of those ancient collisions in space.
Discovered in 2016, Kamoʻoalewa, also known as 2016 HO3, is one of the five known quasi-satellites of the Earth. These are rocks that attach quite close to the planet as they orbit the sun. Little is known about Earth’s entourage of space rocks because these objects are so small and faint.
Kamoʻoalewa, for example, it is the size of a Ferris wheel and it moves away from the Earth between 40 and 100 times as much as the moon, since its orbit around the sun is intertwined in and out of that of the Earth. This left astronomers to wonder about the nature of such rocks.
“An object in a quasi-satellite orbit is interesting because it is very difficult to enter this type of orbit, it is not the type of orbit in which an object in the asteroid belt could easily find itself trapped”says Richard Binzel, a planetary scientist at MIT not involved in the new work. Having an orbit nearly identical to that of Earth immediately raises the suspicion that an object like Kamo’oalewa originated in the Earth-Moon system, he says.
The researchers used the Large Binocular Telescope and Lowell Discovery Telescope, respectively in Safford and Happy Jack, Arizona, to scan Kamoʻoalewa in the visible and near-infrared wavelengths. “The real treasure is in the infrared”says Vishnu Reddy, a planetary scientist at the University of Arizona in Tucson. Light at those wavelengths contains important clues to minerals in rocky bodies, helping to distinguish objects such as the moon, asteroids and terrestrial planets.
Kamoʻoalewa: maybe not just speculation
Kamoʻoalewa reflected more sunlight at longer or redder wavelengths. This pattern of light, or spectrum, looked unlike any other known near-Earth asteroid, Reddy and colleagues found. But they looked like grains of silicate rock from the moon brought back to Earth by Apollo 14 astronauts. “For me”, says Binzel, “The main hypothesis is that it is a fragment ejected from the moon, by a crater event”.
Martin Connors, who was involved in the discovery of Earth’s first known quasi-satellites but was not involved in the new research, also suspects that Kamo’oalewa is a small fragment of the old moon. “This is a well-founded proof”says Connors, a planetary scientist at Athabasca University in Canada. But, he warns, “This does not mean that it is right”.
More detailed observations could help confirm that Kamoʻoalewa is made of lunar material. “If you really wanted to put that nail in the coffin, you would want to go visit, or meet with this little quasisatellite and make many close observations”says Daniel Scheeres, a planetary scientist at the University of Colorado Boulder not involved in the work. “The best thing would be to get a sample.”
The Chinese space agency has announced plans to send a probe to Kamo’oalewa to collect some rock and bring it back to Earth at the end of this decade.
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