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Arxiv: JWST sighting of decameter main-belt asteroids and view on meteorite sources Published: 2/3/2025 9:00:03 PM Updated: 2/3/2025 9:00:03 PM

Paper abstract: Asteroid discoveries are essential for planetary-defense efforts aiming toprevent impacts with Earth, including the more frequent megaton explosions fromdecameter impactors. While large asteroids (>=100 km) have remained in themain belt since their formation, small asteroids are commonly transported tothe near-Earth object (NEO) population. However, due to the lack of directobservational constraints, their size-frequency distribution--which informs ourunderstanding of the NEOs and the delivery of meteorite samples toEarth--varies significantly among models. Here, we report 138 detections of thesmallest asteroids (\gtrapprox 10 m) ever observed in the main belt, whichwere enabled by JWST's infrared capabilities covering the asteroids' emissionpeaks and synthetic tracking techniques. Despite small orbital arcs, weconstrain the objects' distances and phase angles using known asteroids asproxies, allowing us to derive sizes via radiometric techniques. Theirsize-frequency distribution exhibits a break at {~}100 m (debiasedcumulative slopes of q = -2.66\pm0.60 and -0.97\pm0.14 for diameterssmaller and larger than ~ 100 m, respectively), suggestive of a populationdriven by collisional cascade. These asteroids were sampled from multipleasteroid families--most likely Nysa, Polana and Massalia--according to thegeometry of pointings considered here. Through additional long-stare infraredobservations, JWST is poised to serendipitously detect thousands ofdecameter-scale asteroids across the sky, probing individual asteroid familiesand the source regions of meteorites "in-situ".