An Update on Asteroid 2024 YR4 from JWST

The chances of the asteroid 2024 YR4 striking Earth in 2032 have tumbled from a peak of 3.1% in February 2025 to nearly zero today, though a collision with the Moon is still possible. Brand new JWST observations give a fresh perspective on this near-Earth asteroid.

From Discovery to Today

On 27 December 2024, the Asteroid Terrestrial-impact Last Alert System (ATLAS) spotted an asteroid, cataloged as 2024 YR4, with a slim chance of a collision with Earth on 22 December 2032. As observations rolled in, the probability of 2024 YR4 slamming into Earth crept upward, reaching a peak of 3.1% on 18 February 2025. Just a few days later, revised estimates of the asteroid’s orbit reduced the odds of an Earth impact to just 0.004%. Though 2024 YR4 no longer poses a threat to Earth, there is still a small chance it will hit the Moon in 2032.

A New Look at 2024 YR4

As reported today in Research Notes of the AAS, a team led by Andrew Rivkin (The Johns Hopkins University Applied Physics Laboratory) used JWST to observe 2024 YR4 in March 2025. Using the Mid-Infrared Instrument (MIRI) and the Near-Infrared Camera (NIRCam), the team determined the size, albedo, and spectral energy distribution of the asteroid.

By modeling the asteroid’s thermal emission, Rivkin’s team estimated 2024 YR4’s diameter to be 60 ± 7 meters (197 ± 23 feet). This is consistent with previous size estimates that used measurements of the asteroid’s apparent magnitude and estimates of its albedo, or the fraction of light that is reflected from its surface. As a comparison, the asteroid that caused the Tunguska event — an air burst that toppled millions of trees, shattered windows, and sparked forest fires — is thought to have been in the range of 40–100 meters (130–328 feet).

Further Findings and Future Directions

The asteroid’s albedo is between 0.08 and 0.18, with a best-fit value of 0.13. Many classes of asteroids have albedos in this range, so this estimate doesn’t place 2024 YR4 in any particular class. However, Rivkin’s team noted that these values are compatible with previous spectra of the asteroid that suggest an S-type (stony) classification.

The team also estimated the potential impact of a 2024 YR4-like asteroid, finding that a collision with Earth would release the energy equivalent of 2–30 megatons of TNT, with a blast damage radius of up to 80 kilometers (50 miles).

Future modeling using sophisticated thermophysical models will help to define the asteroid’s properties further. And in early 2026, researchers may have another chance to observe 2024 YR4 with JWST and refine their understanding of a potential lunar impact in 2032.

Citation

“JWST Observations of Potentially Hazardous Asteroid 2024 YR4,” A. S. Rivkin et al 2025 Res. Notes AAS 9 70. doi:10.3847/2515-5172/adc6f0