Fastest-spinning near-Earth asteroid: half-meter impactor 2024 XA1 clocks a 1.63-second rotation record

A stone roughly half a meter across was photographed by the Lijiang 2.4-meter telescope one hour before it entered Earth's atmosphere. A year and a half later, it has become the fastest-rotating known near-Earth asteroid: one full rotation every 1.63 seconds. The research, led by Zhang Xiliang and Fan Xiangyu of Yunnan Observatories, Chinese Academy of Sciences, was published in The Astronomical Journal on October 16 and brought to public attention by Science and Technology Daily on October 25. It resets two boundaries at once: how fast an asteroid can spin, and how much information can be extracted from a single streak of light on an image.

The event: the 11th impact warning, ten hours ahead

At 05:54 UTC on December 3, 2024, the Bok Telescope at Kitt Peak, Arizona spotted a one-meter-sized moving target. Ten hours later it entered the atmosphere over eastern Siberia and became a fireball. This was the 11th successfully predicted asteroid impact (13 such events are known to date, all meter-scale objects, with warning times ranging from 2 to 21 hours). ESA's Meerkat system issued an alert two hours after discovery; one hour before the fall, the Lijiang telescope waited at the predicted position and captured images in the final window. At the time, the Yunnan Observatories team's contribution was "we photographed it"; now it is "we read it."

A trailing image as a time series

The difficulty lay in the image morphology. The asteroid was moving so fast that it left not a point but a bright streak on the CCD. Conventional astronomical photometry assumes one frame corresponds to one moment in time, and completely fails on trailed images. The team's method treats the streak as a time axis: brightness is extracted segment by segment along the motion track, then verified by comparing model images against the original frame, fully reconstructing how brightness changed over time (the light curve). The rotation period is read from the periodicity of that curve: 1.63 seconds, nearly 40% faster than the previous record of 2.58 seconds held by 2024 BX1.

Why 1.63 seconds is a verdict on internal structure

Spin rate is a lie detector for a body's interior. Rubble piles held together loosely by their own gravity have a spin limit: spin too fast, surface centrifugal force exceeds gravity, and the whole thing flies apart. The critical period depends on density—about two hours for typical asteroid density. Note: hours. The surface centrifugal acceleration at a 1.63-second period far exceeds gravity, leaving only one possible answer: this is not a rubble pile, but a monolithic body whose solid form is maintained by the mechanical strength of the rock itself.

How could a half-meter stone hold together? The team offers two possible origins: it could be a fragment ejected when a larger body collided and broke apart, or the YORP effect (tiny torques from sunlight reflected off the surface) gradually spun it up over time. Both point to the same kind of birth: it is a survivor of a larger destructive event, with no internal cracks for centrifugal force to exploit.

Whether it hits is one question; whether it spins is another

The methodology applies more broadly than this one stone. As of October 10, 2026, 42,752 near-Earth asteroids have been confirmed, of which 2,542 are potentially hazardous. The difficulty of warning has never been discovery—it is characterization: meter-scale objects are small, faint, and fast, observation windows are measured in hours, and physical parameters are nearly impossible to obtain. The trailed photometry pipeline established here turns "a bright streak" into a source of three parameters: period, shape, and structure. In the next short-warning event, this method can directly output the quantities most needed for impact energy assessment.

One common misconception worth correcting: asteroid defense exercises never target 1.63-second spinners like this one—they burn up in the atmosphere, often without even a fireball reaching the ground. The real threat is potentially hazardous objects above 140 meters, and their rotation and structure parameters are obtained with exactly the same photometric technique. Reading the streak of a half-meter stone is a rehearsal for reading the streaks of much larger rocks.

References

• Zhang Xiliang, Fan Xiangyu et al.: Light-curve reconstruction and rotation period study of 2024 XA1, The Astronomical Journal (published 2026-10-16)
• Science and Technology Daily: One rotation every 1.63 seconds! Chinese researchers confirm the fastest-rotating known near-Earth asteroid (2026-10-25)
• Fenucci et al.: The fall of asteroid 2024 XA1 and the location of possible meteorites (Icarus, 2025)
• Global Times: Chinese-led research team identifies fastest-rotating near-Earth asteroid (2026-10)
• Guangming Online: A near-Earth asteroid hit Earth—and Yunnan observed it! (2024-12-10)