JWST Characterization of Earth Quasi-Satellite (469219) Kamo`oalewa

Near-Earth asteroid (469219) Kamo`oalewa 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 February 2026. The JWST reflectance spectrum is notably less red (more neutral) from 1.0-2.5 mu m than previous ground-based spectrophotometric observations. New observations made with LBT in April 2026, observed and processed similarly to the 2021 observations, find zJ colors in agreement with JWST. Kamo`oalewa's infrared colors appear more similar to S, V, or E-type silicate 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 plus or minus 0.01 mu m. We do not detect a 2.0 mu m silicate absorption. Models of Kamo`oalewa's faint thermal emission (beginning near 4.5 mu m) find a mean diameter of D=18 plus or minus2 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. Kamo`oalewa's brightness variations over the course of the JWST program provides independent confirmation of its rotation period of 27.9 minutes, with an axis ratio about1.4 (D about15-21 m).