Apache Point Rapid Response Characterization of Primitive Imminent Impactor 2024 RW₁

Abstract Imminent impactors may be detected only a few hours before their impact with Earth, providing a brief opportunity to characterize them before impact. We describe the characterization of imminent impactor 2024 RW 1 , which was discovered by the Catalina Sky Survey on 2024 September 4 at 05:43 UTC, before it entered the atmosphere near the northern Philippines at 16:39 UTC. We observed 2024 RW 1 with the Astrophysical Research Consortium Telescope Imaging Camera on the Apache Point Astrophysical Research Consortium’s 3.5 m telescope on 2024 September 4 at 10:16 UTC. We obtained g , r , i , and z photometry of 2024 RW 1 , yielding color indices of g – r = 0.47 ± 0.04, r – i = 0.13 ± 0.04, i – z = –0.11 ± 0.07, and g – i = 0.60 ± 0.04, corresponding to a spectral slope of 0.67 ± 0.40 %/100 nm. The closest match to an asteroid spectral type is with B-type asteroids from the C complex. We detect variations in the time-series photometry of the asteroid with an amplitude of ∼0.75, and a double-peaked rotation period of ∼1900 s. Assuming a visible albedo of 0.07 ± 0.03, a density of ∼1500 kg m −3 , and a calculated absolute magnitude of 30.92 ± 0.05, we estimate that the asteroid has a diameter of 3.3 ± 0.7 m and a total mass of ∼28,000 kg. Comparing our astrometric orbital solutions to NEOMOD3, the most likely source of 2024 RW 1 is the 3:1 main-belt mean-motion resonance (77% probability) followed by the ν 6 resonance (13% probability), consistent with its organic B-type nature.