Thermophysical characterization of the potentially hazardous near-Earth object 2024 YR4
Abstract
The asteroid 2024 YR_4 is a potentially hazardous Apollo-type near-Earth object. Its highly eccentric orbit produces close Earth-Moon encounters roughly every 4 years. Based on the astrometry collected during the discovery apparition, the asteroid had a 4% probability of a lunar impact on 2032 December 22. A collection of light curves, including JWST-NIRCam data, allowed us to constrain the rotation period, spin pole, and convex shape solutions for the object. We analyzed two sets of JWST-MIRI observations obtained in three filters on 26 March 2025. The extracted photometry reveals rotationally driven thermal flux variations. The combination of a spin-shape model from light-curve inversion and the absolutely calibrated three-band mid-infrared light curves is well reproduced by a convex spin-shape solution with a spin pole at (λ_ecl, β_ecl) = (232 ±1̧irc, -11 ±3^̧irc), a sidereal period of 19.4633 (± 0.0001),min, and axis ratios of a/b ≈ 1.28 and b/c ≈ 1.45. The corresponding equivalent-volume diameter is +1.8 _ -3.6 ,m, with a geometric V-band albedo of p_V = 0.11^ +0.05 _ -0.03 (assuming H_V = 24.14 ±0.25,mag). A high thermal inertia Γ $>500,J,m-2,K^-1,s$^ -1/2 and low surface roughness are required to explain the observed MIRI data. The rapid rotation, in combination with the high thermal inertia, leads to significant heat transport to the night side, producing a broad nearly isothermal equatorial band. The near-Earth asteroid thermal model has limited reliability for this object, requiring an extreme beaming parameter η > 3, whereas the fast-rotating model and a full thermophysical model provide consistent and reliable estimates of the size and albedo. The combination of high eccentricity and high thermal inertia implies seasonal skin depths of up to ∼3,m and radiative timescales of weeks to months. Although seasonal heating is negligible for the March 2025 observations because of the near-equator-on viewing geometry, the seasonal Yarkovsky drift is expected to be dominant over the diurnal component and might become measurable during future encounters. Although JWST astrometry from February 2026 rules out any possible impact on the Earth or the Moon for at least 100 years, the spin, shape, and radiometric constraints presented here provide an important benchmark for future potentially hazardous objects.