Asteroid 2024 YR4 Is Carrying Heat Into Its Night
It spins once every 19.46 minutes, yet its surface barely follows day and night. JWST data show asteroid 2024 YR4 moving heat into a broad, nearly even-temperature belt.
The Twenty-Minute World
Asteroid 2024 YR4 briefly became famous for the wrong reason: early observations left a small chance that it would strike the Moon in 2032. The impact corridor is now closed, but the James Webb Space Telescope has revealed a different kind of extreme.
A study published on 16 September in Astronomy & Astrophysics combines visible-light curves with three bands of Webb mid-infrared data. Its preferred model gives the asteroid a rotation period of 19.4633 minutes and an elongated shape, with one principal axis roughly 1.28 times another.
This asteroid turns a full day into less than a coffee break.
The Night That Stays Warm
The infrared brightness changed as the object rotated, but ordinary asteroid-temperature assumptions could not reproduce the pattern cleanly. The researchers found that the surface needs high thermal inertia — above 500 joules per square metre per kelvin per square-root second — together with low surface roughness.
That combination lets stored heat move far beyond the sunlit face. In the model, rapid rotation produces a broad equatorial belt with nearly even temperatures across day and night.
- A standard near-Earth asteroid thermal model required an extreme beaming value above 3.
- A fast-rotator model and a full thermophysical model gave consistent size and reflectivity estimates.
- Seasonal heating reaches as much as about three metres below the surface in the model.
Webb did not resolve rocks or dust on the asteroid. These properties are inferred from the way its thermal glow changes, not from a close-up surface image.
The Danger Clock Closed
Discovery-era astrometry once left about a 4 percent lunar-impact probability for 22 December 2032. Webb observations from February 2026 ruled out an impact with either Earth or the Moon for at least a century. The label "potentially hazardous" describes its orbit and size class; it is not a current impact forecast.
The paper predicts that seasonal heating should push the asteroid's orbit more strongly than the ordinary day-night Yarkovsky effect. Future close encounters can test that drift.
2024 YR4 is no longer an approaching impact story. It is now a benchmark for how a dangerously fast, thermally stubborn small world carries sunlight into darkness.