Telescope-to-Fireball Characterization of Earth Impactor 2022 WJ1

Comparing how an asteroid appears in space to its ablation behaviour during atmospheric passage 21 and finally to the properties of associated meteorites represents the ultimate probe of small near-Earth 22 objects. We present observations of 2022 WJ1, an Earth impactor which disrupted over the North 23 American Great Lakes on 19 November 2022, from the Lowell Discovery Telescope and from multiple 24 meteor camera networks. As far as we are aware, this is only the second time an Earth impactor 25 has been specifically observed prior to impact to characterize its composition. The orbits derived 26 from ground-based meteor cameras and telescopic observations submitted to the Minor Planet Center 27 (MPC) result in impact trajectories that agree to within 40 meters, but no meteorites have been 28 found as of yet. The telescopic observations suggest a silicate-rich surface, and thus a moderate-to29 high albedo, which results in an estimated size for the object of just D = 40 − 60 cm. Modeling the 30 fragmentation of 2022 WJ1 during its fireball phase also suggests an approximate half-meter original 31 size for the object as well as an ordinary chondrite-like strength. These two lines of evidence both 32 support that 2022 WJ1 was likely an S-type chondritic object and the smallest asteroid compositionally 33 characterized in space. We discuss how best to combine telescopic and meteor camera datasets, how 34 well these techniques agree, and what can be learned from studies of ultra-small asteroids.