JWST reveals Kamo`oalewa asteroid is enstatite-rich, not lunar-like, with 18-meter diameter
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[Submitted on 22 Jun 2026 (v1), last revised 29 Jun 2026 (this version, v2)]
Summary
JWST observations of near-Earth asteroid (469219) Kamo`oalewa — a stable quasi-satellite of Earth and target of China's Tianwen-2 mission — reveal a less red (more neutral) reflectance spectrum than previously thought. The infrared colors resemble S, V, or E-type silicate asteroids rather than space-weathered lunar-like silicates. A faint silicate absorption at 0.93 μm is detected, but no 2.0 μm absorption. Thermal emission modeling gives a mean diameter of 18±2 meters and a best-fit visible albedo of 0.59, suggesting an oldhamite-bearing enstatite-rich composition. Brightness variations confirm a 27.9-minute rotation period with an axis ratio of ~1.4.
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Twitter / XJWST reveals Kamo`oalewa asteroid is enstatite-rich, not lunar-like, with 18-meter diameterarxiv.orgKey quotes
· 5 pulledThe JWST reflectance spectrum is notably less red (more neutral) from $1.0-2.5$ $\mu m$ than previous ground-based spectrophotometric observations.
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.
Models of Kamo`oalewa's faint thermal emission (beginning near 4.5 $\mu m$) find a mean diameter of $D=18\pm2\mathrm{m}$ and best-fit visible albedo $p_V = 0.59^{+0.25}_{-0.17}$
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 $\sim1.4$ ($D\sim15-21$ m).
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