Apache Point rapid response characterization of primitive imminent impactor 2024 RW$_1$

TL;DR

This paper details rapid observational characterization of the imminent impactor 2024 RW$_1$, including its spectral type, rotation, size, and probable origin, providing crucial data shortly before atmospheric entry.

Contribution

It presents the first rapid response observational analysis of an imminent impactor, including spectral, photometric, and orbital data, shortly before impact.

Findings

Spectral type consistent with B-type asteroid from C-complex.

Estimated diameter of approximately 3.3 meters.

Likely origin from the 3:1 main belt resonance.

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 10:16 UTC. We obtained g, r, i, and z photometry of 2024 RW$_1$, yielding color indices of g-r = 0.47$\pm$0.04, r-i = 0.13$\pm$0.04, i-z = -0.11$\pm$0.07, and g-i = 0.60$\pm$0.04, corresponding to a spectral slope of 0.67$\pm$0.40~$\%$/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 $\sim$0.75, and a double-peaked rotation period of $\sim$1900 s. Assuming a visible albedo of 0.07$\pm$0.03, a density of $\sim$1500 kg/m$^3$, and a calculated absolute magnitude of 30.92$\pm$0.05, we estimate that the asteroid has a diameter of 3.3$\pm$0.7 m and a total mass of $\sim$28,000 kg. Comparing our astrometric orbital solutions to NEOMOD3, the most likely source of 2024 RW$_1$ is the 3:1 main belt mean motion resonance (77\% probability) followed by the $\nu_6$ resonance (13\% probability), consistent with its organic B-type nature.