¹Benjamin N. L. Sharkey, ²Vishnu Reddy, ³John W. Noonan, ⁴Theodore Kareta, ¹James M. Bauer, ⁵Bryan J. Holler, ¹Yaeji Kim, ⁶Albert R. Conrad
The Astrophysical Journal Letters, 1010, L31
Open Access Link to Article [DOI: 10.3847/2041-8213/aea6b6]
¹Department of Astronomy, University of Maryland College Park, MD 20742-2421, USA
²Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
³Department of Physics, Edmund C. Leach Science Center, Auburn University, Auburn, AL, USA
⁴Department of Astrophysics and Planetary Science, Villanova University, Villanova, PA, USA
⁵Space Telescope Science Institute, Baltimore, MD, USA
⁶Large Binocular Telescope Observatory, Tucson, AZ, USA

Near-Earth asteroid (469219) Kamoʻoalewa is a uniquely stable quasi-satellite of the Earth and a target of the Tianwen-2 spacecraft mission. Here we report observations taken with JWST’s NIRSpec instrument in integral field unit (IFU) mode in 2026 February. The JWST reflectance spectrum is notably less red (more neutral) from 1.0 to 2.5 μm than previous ground-based spectrophotometric observations. New observations made with the Large Binocular Telescope (LBT) in 2026 April, observed and processed similarly to the 2021 observations, find zJ colors in agreement with JWST. Kamoʻoalewa’s infrared colors appear more similar to typical silicate-rich asteroids and unlike the reddened, space-weathered lunar-like silicates suggested by previous observations. In agreement with the ground-based spectrum, we detect a faint silicate absorption feature at 0.93 ± 0.01 μm. We do not detect a 2.0 μm silicate absorption. Models of Kamoʻoalewa’s faint thermal emission (beginning near 4.5 μm) find a mean diameter of D = 18 ± 2 m and best-fit visible albedo p_V = 0.59^+0.25_−0.17, with models as low as p_V = 0.36 providing adequate model fits. This combination of color, albedo, and absorption bands is similar to oldhamite-bearing enstatite-rich compositions. Kamoʻoalewa’s brightness variations over the course of the JWST program provide independent confirmation of its rotation period of 27.9 minutes, with an axis ratio ∼1.4 (D ∼ 15–21 m).