A curious space rock has just gotten curiouser. The asteroid Kamo`oalewa has an odd orbit that makes it almost a mini-moon of Earth – and now it may really earn that title, as new observations show that it could in fact be a fragment of the Moon.
Discovered in 2016, Kamo`oalewa measures about 40 m (130 ft) wide and rotates once every 28 minutes or so. Technically it orbits the Sun, but it also kind of orbits Earth at a distance 13.6 times further than the Moon, alternating between swinging out ahead of us and lagging behind. That makes it a “quasi-satellite.”
Despite its relative proximity to Earth, Kamo`oalewa is tricky to study, being small, faint and only visible for a few weeks every April. So for the new work, astronomers peered through that window earlier this year to study the elusive rock using the Large Binocular Telescope (LBT) and the Lowell Discovery Telescope (LDT).
The team measured the object’s spectrum, the pattern of light that reflects off its surface. Because different elements reflect and absorb different wavelengths of light, scientists can use an object’s spectrum to determine what it’s composed of. In this case, Kamo`oalewa was mostly silicate-based.
That fingerprint didn’t match any other known near-Earth asteroid, the team says. The closest match was to lunar rocks brought back by Apollo astronauts, suggesting Kamo`oalewa is a piece of the Moon that broke off at some point, perhaps during some kind of impact event. That would make it the first known asteroid of lunar origin, and its unusual orbit lends weight to that hypothesis.
"It is very unlikely that a garden-variety near-Earth asteroid would spontaneously move into a quasi-satellite orbit like Kamo`oalewa's," says Renu Malhotra, co-author of the study. "It will not remain in this particular orbit for very long, only about 300 years in the future, and we estimate that it arrived in this orbit about 500 years ago."
Further work by the team will focus on tracking down Kamo`oalewa’s origins in more detail.
The research was published in the journal Nature Communications Earth and Environment.
Source: University of Arizona
