Spectral Constraints on the Surface Material of Asteroid (469219) Kamoʻoalewa

Abstract

Recent JWST observations reveal that the Earth’s quasi-satellite (469219) Kamoʻoalewa possesses a high geometric albedo and a flat near-infrared spectrum, in contrast with earlier ground-based observations, posing new challenges to its compositional identification. This study evaluates the potential surface composition of Kamoʻoalewa by combining its ground-based visible spectrum with JWST photometric and spectral data. Integrated constraints from spectral profiles and absolute reflectance identify FeO-free synthetic anorthite and aubrites as the primary candidate materials. While spectrally featureless and indistinguishable in the visible and near-infrared, these two candidates can be resolved in the mid-infrared by the thermal emission spectrometer onboard China’s Tianwen-2 mission. Importantly, a subtle absorption feature in the 1.2–2.1 μm range detected by JWST–absent in common silicate minerals–may serve as the key to identifying Kamoʻoalewa’s true nature, suggesting it likely represents a novel, previously uncharacterized class of small body.