China's Tianwen-2 spacecraft has achieved a remarkable feat, chasing Earth's tiny quasi-moon, Kamoʻoalewa, for an astonishing 400 days and 1 billion kilometres. This mission has returned the first close-up image of Kamoʻoalewa, taken from just 20 kilometres away on July 2, 2026. The image reveals an uneven, angular body, only a few tens of metres across, leaving scientists intrigued about its origin and composition.
The spacecraft's long journey and approach to Kamoʻoalewa have provided valuable insights. Initially, the leading theory suggested that Kamoʻoalewa was a fragment blasted from the Moon, influenced by a 2021 study by Benjamin Sharkey. However, recent developments have cast doubt on this hypothesis.
One significant challenge arises from a population study by Marco Fenucci and colleagues, who modelled both ordinary near-Earth asteroids and fragments from the Giordano Bruno impact on the Moon. Their findings indicate that the main-belt population is more likely to produce Kamoʻoalewa-like objects, challenging the lunar origin theory.
Another intriguing development is the reanalysis of Kamoʻoalewa's spectrum by Pengfei Zhang's team. They found that the absorption feature aligns with LL chondrites, a type of stony material associated with asteroids like Itokawa. This discovery suggests an origin in the Flora asteroid family, followed by extensive weathering of the surface material.
Furthermore, Sharkey's new observations using the James Webb Space Telescope reveal a less red spectrum than previously thought, resembling silicate asteroid classes rather than weathered lunar material. These results collectively imply that Kamoʻoalewa may not be lunar rock, challenging the initial hypothesis.
While the image provides valuable information about Kamoʻoalewa's shape and size, it cannot definitively determine its origin. The spacecraft's next milestones, including lower-altitude mapping and sample collection, will be crucial in resolving the ambiguity. The returned sample will enable laboratory measurements to compare Kamoʻoalewa's composition with lunar samples and known meteorite groups, providing the ultimate answer to its mysterious origin.
