1,3,5,6,5,6,10,12- 1Max-Planck-Institut fuer Extraterrestrische Physik, HEG, Garching, Germany (tmueller@mpe.mpg.de)
- 2Department of Physics, University of Helsinki, Helsinki, Finland
- 3Space Telescope Science Institute, Baltimore, MD, USA
- 4Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
- 5Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
- 6European Space Agency – ESRIN, Frascati, Italy
- 7NASA Ames Research Center, CA, USA
- 8Jet Propulsion Laboratory, CA, USA
- 9Association of Universities for Research in Astronomy, Washington, DC, USA
- 10Jet Propulsion Laboratory, MD, USA
- 11Ondřejov Observatory, Ondřejov, Czechia
- 12Northern Arizona University, AZ, USA
The Apollo-type near-Earth asteroid (NEA) 2024 YR4 was discovered on 25 December 2024, only a few hours after it had passed Earth at a distance of approximately 2.2 lunar distances. In December 2028, it will again approach the Earth-Moon system, this time at a distance of about 20 lunar distances. As of this writing, it has a 3.8% impact probability with the Moon on 22 December 2032.
The orbit of 2024 YR4 is highly eccentric and has a low inclination (semi-major axis a = 2.52 au, eccentricity e = 0.66, inclination i = 3.4°), crossing the orbits of Earth (perihelion at 0.85 au), Mars, and even extending beyond the main asteroid belt (aphelion at 4.18 au). The object is estimated to be about 60 ± 7 meters in diameter (Rivkin et al. 2025a), with a rotation period of approximately 19.5 minutes, based on lightcurves showing ~0.4 mag variations (P. Pravec, SBO-NASA mailing list, 03-Jan-2025). An initial lightcurve inversion analysis by Bolin et al. (2025) suggests an oblate shape with an axial ratio of ~3:1 and a spin axis oriented towards (l, b) = (~42°, ~−25°). Its measured color indices are consistent with S-type or L-/K-type asteroids.
To date, no radar observations or successful occultation measurements have been obtained, and the size estimate is based solely on a simple radiometric analysis using single-epoch, three-band JWST/MIRI observations.
We conducted a combined JWST/NIRCAM and MIRI multi-epoch observing campaign (Rivkin et al. 2025b). Here, we re-analyzed all available MIRI imaging data from March and May 2025 using advanced post-processing and filtering techniques. Our flux extraction and uncertainty estimates were validated against faint calibration stars and then applied consistently across various data products: from single calibrated integration images and per-dither images to combined 4-dither, multi-integration mosaics per band. The observations on March 26, 2025 (r = 1.81 au, D =1.08 au, a = 28°) in filters F1000W, F1280W, and F1500W covered one full rotation of the asteroid, while the May F1000W observations (YR4 located at the inner asteroid belt region beyond 2 au, but still seen under a similar phase angle of about 28°) captured three full rotations.
We applied simple thermal models, including the Near-Earth Asteroid Thermal Model (NEATM; Harris 1998) and the Fast-Rotation Model (FRM; Lebofsky et al. 1978), to derive estimates of size, albedo, and beaming parameter. In parallel, we used thermophysical modeling (TPM; Lagerros 1998; Delbo et al. 2015, and references therein) to test various spin and shape solutions (Bolin et al. 2025; MacLennan et al. 2025), constrain thermal properties, and refine the size–albedo solution. The final TPM results are discussed in the context of other decameter-scale asteroids (e.g., Burdanov et al. 2025).
Our analysis also provides a basis for predicting future JWST observing opportunities for YR4 and offers improved constraints on non-gravitational forces acting on the asteroid, which are relevant for long-term orbit predictions and impact risk assessment.
Acknowledgement:
P.P. has been supported by the "Praemium Academiae" award by the Academy of Sciences of the Czech Republic, grant AP2401.
References:
- Bolin, B.T., Hanuš, J., Denneau, L., Bonamico, R., Abron, L.-M., et al., The Discovery and Characterization of Earth-crossing Asteroid 2024 YR4, The Astrophysical Journal Letters, 984, L25, 12 pp (2025)
- Burdanov, A. Y., de Wit, J., Brož, Müller, T.G., Hoffmann, T., et al., JWST sighting of decametre main-belt asteroids and view on meteorite sources, Nature, 638, 74 (2025)
- Delbo, M., Mueller, M., Emery, J., Rozitis, B, Capria, M.T., Asteroid Thermophysical Modeling, in Asteroids IV, Patrick Michel, Francesca E. DeMeo, and William F. Bottke (eds.), University of Arizona Press, Tucson, 895 pp, ISBN: 978-0-816-53213, p107-128 (2015)
- Harris, A.W., A Thermal Model for Near-Earth Asteroids, Icarus 131, 291-301 (1998)
- Lagerros, J.S.V, Thermal physics of asteroids, PhD Thesis, Uppsala University, 377L (1998)
- Lebofsky, L.A., Veeder, G.J., Lebofsky, M.J., Matson, D.L., Visual and Radiometric Photometry of 1580 Betulia, Icarus, 35, 336-343 (1978)
- MacLennan, E., et al., Shape and Spin Properties of 2024 YR4 from Multi-filter Lightcurve Observations, EPSC/DPS 2025 (2025)
- Rivkin, A.S., Müller, T.G., MacLennan, E., Holler B., Burdanov, A., et al., JWST Observations of Potentially Hazardous Asteroid 2024 YR4, Research Notes of the AAS, 9, 70 (2025a)
- Rivkin, A.S., et al., JWST MIRI and NIRCAM Observations of Potentially Hazardous Asteroid 2024 YR4, EPSC/DPS-2025 (2025b)
How to cite: Müller, T., MacLennan, E., Holler, B., Burdanov, A., de Wit, J., Rivkin, A., Conversi, L., Devogele, M., Dotson, J., Farnocchia, D., Glantzberg, A., Hammel, H., Micheli, M., Milam, S., Pravec, P., and Thomas, C.: A Thermophysical Model Study for 2024 YR4 based on JWST/MIRI Measurements, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-934, https://doi.org/10.5194/epsc-dps2025-934, 2025.
