Our Moon seems careless.
A new analysis has shown that a piece of rock found near Earth's orbital path and the Sun appears to be made from the same material as that of the Moon. This suggests that it was thrown into space at some point. It remains to be determined how and when this happened.
Named 469219 Kamooalewa by astronomers, the rock was already interesting before this latest development.
This object is part of a group of asteroids called the Apollo asteroids. They orbit Earth around the Sun more or less the same as Apollo, but Kamooalewa, also known as a quasi satellite, is able to stay close to Earth for long periods and multiple orbits.
Kamooalewa, which is only 46 to 58 meters in diameter (150-190 feet) can be seen in the Earth's skies for a few weeks each April. It was only discovered in 2016, so it's been difficult to learn more.
Researchers used the Large Binocular Telescope (Mount Graham International Observatory) to help them learn more. 2017 observations included the asteroid spectrum, which is the distinctive pattern created by Kamooalewa's reflection of light from the Sun.
Initial results revealed that Kamooalewa had a spectrum that was very similar to the one generated by the Apollo missions' lunar rocks. It is unlike any other asteroids. The researchers were puzzled by this result and wondered if the asteroid was made from the same material as the Moon.
Ben Sharkey, an astronomer at the University of Arizona, stated that he had compared every near-Earth asteroid spectrum available to him and found no match.
It is obvious to collect more data when you come across something unusual. Kamooalewa found this difficult because it had a limited viewing window and because the COVID-19 global epidemic resulted in reduced telescope operations at observatories around Earth, including Mount Graham.
Researchers were only able to observe more of the mysterious rock from the sky until April. These observations confirmed their earlier findings that Kamooalewa, for some unknown reason, reflects light more like the Moon, than any other asteroids.
There are many possible explanations for Kamooalewa’s origin. It could have been captured from another asteroids to its current orbit.
According to researchers, this is highly unlikely. Kamooalewa’s orbit deviates very little from Earth's plane, unlike other asteroids. Kamooalewa has the same orbital period and inclination as Earth.
Renu Malhotra, a University of Arizona planetary scientist, says that it is unlikely that an asteroid of garden variety near Earth would move into a quasisatellite orbit such as Kamooalewa’s.
"It won't stay in this particular orbit for too long, only about 390 years in the future. We estimate that it entered this orbit around 500 years ago."
Another possibility is Kamooalewa could have originated from a population of near Earth asteroids. This population hangs out in a region of Earth's orbit known for being gravitationally stable, called a Lagrangian Point. We will need to discover evidence that this population of asteroids exists in order to confirm this.
The best possible fit, based on the current information, is that Kamooalewa was either a fragment that fell off in a lunar collision event (pretty plausible given the amount of impact craters our satellite has) or an asteroid which drew too close in orbit to Earth and Moon and was broken up by gravitational interactions.
The researchers believe that the Moon chunk scenario is the most appropriate, given Kamooalewa’s spectrum.
Nature Communications published the study.
