Where did Earth’s oddball ‘quasi-moon’ come from? Scientists pinpoint famed lunar crater
By DANIEL CLERY, Science.
Excerpt: Astronomers suspect an unusual near-Earth rocky object is not a typical escapee from the Solar System’s asteroid belt, but is instead a chunk of the Moon blasted into space eons ago by a spectacular impact. Now, a team of researchers has modeled what sort of lunar impact could have ejected such a gobbet of Moon and deposit it in a stable, nearby orbit. Surprisingly, only one strong candidate emerged: the asteroid strike that created the famous Giordano Bruno crater, the youngest large crater on the Moon, the group reports today in Nature Astronomy. ...The odd asteroid, known as 469219 Kamo‘oalewa, was discovered in 2016 ...measures between 40 and 100 meters across and rotates particularly fast—once every 28 minutes. It follows an elliptical orbit around the Sun that moves in sync with Earth, giving the impression that the asteroid orbits Earth, even though it is outside the planet’s gravitational influence. The asteroid’s curious orbit and small size led to it being chosen as the first target for China’s sample return mission Tianwen-2, set for launch in 2025. ...Interest in the asteroid heightened in 2021, when studies by the Large Binocular Telescope Observatory in Arizona first suggested its composition more closely resembles a Moon rock than a typical asteroid. The spectrum of the light reflected off Kamo‘oalewa revealed silicates more typical of a lunar sample...