Lunar origin of Earth quasi-satellite Kamoʻoalewa

Abstract

Asteroid Kamoʻoalewa is an Earth quasi-satellite that orbits the Sun along the same path as Earth. Its visible and near-infrared reflectance spectrum, observed from Earth-based telescopes, is highly reddened and differs from typical spectra of main belt asteroids, but resembles that of space-weathered lunar samples, suggesting a lunar origin. However, whether Kamoʻoalewa originated from the Moon remains unknown. Here, we report that Kamoʻoalewa’s spectrum closely matches the in-situ spectra observed by Yutu-1 and Yutu-2 rovers, and the laboratory-measured spectra of Chang’E-5 lunar soils, which supports its lunar origin. We further find, based on the Moon Mineralogy Mapper’s hyperspectral observations, a widespread presence of spectra similar to that of Kamoʻoalewa on the lunar nearside, particularly in regions around Tycho, Aristarchus, Glushko, Thales, and Proclus craters. Our modeling of impact-induced fragments and their subsequent dynamical trajectories indicates that only those ejected from Tycho crater could escape the Earth-Moon system and become current Earth’s co-orbitals, suggesting that Tycho is the most likely source crater of Kamoʻoalewa. The lunar origin of Kamoʻoalewa sheds new light on the formation of near-Earth objects and promises to advance our understanding of the Moon’s youthful geological features and complex anorthositic crust through the sampling of this asteroid by the forthcoming Tianwen-2 mission.