A Chip Off the Moon May Be Tailing Earth on Its Orbit Around the Sun

Researchers suspect the fragment may have been debris from a cratering event on the lunar surface

An image of a full moon. The moon looks silver with grey sploches.
Not much is known about mysterious quasisatellites because of their small dimensions, distance, and ability to conceal themselves in the shadows. Kamoʻoalewa is the first quasisatellite to move within observing range of large telescopes. Gregory H. Revera via Wikimedia Commons under CC BY-SA 3.0

The moon, Earth's natural satellite, is riddled with craters from celestial objects crash landing on its surface. After five years of observations, researchers now suspect that an elusive object orbiting Earth, known as 469219 Kamoʻoalewa, may be a fragment of the moon, flung out into space by one of these impacts. When viewed in infrared, the asteroid had silicates and mineral characteristics like the moon, reports Jeff Hecht for Sky & Telescope. Researchers report the first detailed observations of a quasisatellite this month in Communications Earth & Environment.

The 165-foot-long asteroid, also known as 2016 HO3, was discovered in 2016 when researchers spotted it with the Pan-STARRS PS1 telescope at the Haleakalā Observatory in Hawai'i, reports Robin George Andrews for the New York Times. The instrument specializes in detecting asteroids. However, scientists were still unsure about Kamoʻoalewa's origin.

Kamoʻoalewa, which means wobbling object in Hawaiian, is one of Earth's five known quasisatellites. As quasisatellites orbit the sun, they stick close to Earth but never circle our planet as they weave in and out of its own path around the sun, reports Passant Rabie for Inverse. Kamoʻoalewa swings between 9 million miles—about 38 times further than the moon—and at most, 25 million miles away from Earth, per the New York Times. Not much is known about mysterious quasisatellites because of their small dimensions, distance, and ability to conceal themselves in the shadows. Kamoʻoalewa is the first quasisatellite to move within observing range of large telescopes, Sky and Telescope reports.

"An object in a quasisatellite orbit is interesting because it's very difficult to get into this kind of orbit — it's not the kind of orbit that an object from the asteroid belt could easily find itself caught in," says Richard Binzel, a planetary scientist at MIT who was not involved in the study, to Maria Temming for Science News. Because its orbit is nearly identical to Earth's, researchers suspect Kamoʻoalewa may have come from within the Earth-moon system, Binzel adds.

Researchers began to unravel Kamoʻoalewa's origin in 2017 after it was illuminated by the sun. Astronomers gazed at the asteroid with two telescopes in Arizona: the Large Binocular Telescope and the Lowell Discovery Telescope. They used the brief period when the sun shined its light on the space rock to identify what its is made of. The research team collected additional data in 2019 and in the spring of 2021, Inverse reports.

Light reflected off the asteroid revealed that the rock consists of silicates and minerals. There is also evidence of space weathering events, such as micrometeorite bombardment and solar wind particles, per Inverse. Kamo'oalewa reflects sunlight at long and red wavelengths, similar to grains of silicate rock brought back to Earth from the Apollo missions, Science News reports, which supports the hypothesis that the quasisatellite may actually be a chunk of the moon. The object's slow orbit and size are also consistent with the moon origin hypothesis, Sky and Telescope reports.  

 "To me, the leading hypothesis is that it's an ejected fragment from the moon, from a cratering event," Binzel comments to Science News.

More evidence is needed to confirm if Kamo'oalewa is a chip off the ol' moon—and we may find out soon. The Chinese National Space Administration is already planning to collect and return samples from Kamo'oalewa on a mission set to launch in 2024 and arrive in 2025, per Sky and Telescope.

"There's so many different groups of asteroids in the solar system," first author of the study Benjamin Sharkey, a graduate student at the University of Arizona, tells Inverse. "What's really cool about this one is the fact that this is such a rarely studied type of asteroid — quasi satellites."