Summary
A preprint analysing the Rubin Observatory’s Data Preview 2 asteroid catalogue reports two asteroids larger than 2 km completing a rotation in about five minutes. Its method adjusts the complexity of each asteroid’s light-curve model and can retain multiple possible periods when one cannot be selected reliably.
An arXiv preprint analysing the Vera C. Rubin Observatory’s Data Preview 2 (DP2) catalogue reports two asteroids larger than 2 km that each complete a rotation in about five minutes. One, asteroid 491384, is about 2.5 km in diameter; the researchers describe it as the largest known ultra-fast rotator so far.
The study also identifies 66 asteroids rotating faster than the classical 2.2-hour spin barrier. The authors say the two kilometre-scale objects must have significant internal cohesion to withstand their rapid spin.
How the catalogue analysis found the rotations
Astronomers can estimate an asteroid’s rotation from changes in its brightness over time. But survey observations may be sparse and irregular, making it possible for period-search methods to produce several plausible answers.
The researchers developed a method that fits the brightness pattern with a Fourier series—a mathematical way to represent a repeating variation—and chooses the series order separately for each asteroid. When the data do not support one reliable rotation period, the method reports alternative periods with associated probability estimates rather than forcing a single answer.
Applying the method to the Rubin DP2 solar-system-object catalogue, the team determined reliable periods for a large sample of asteroids and found the 66 super-fast rotators. The abstract does not give the sample’s total size.
Why five-minute spins matter
The 2.2-hour spin barrier is a reference point for asteroids: a loosely bound body held together mainly by gravity is expected to have difficulty remaining intact if it rotates much faster. Faster rotation can therefore indicate that a body has internal strength or cohesion beyond gravity alone.
That makes the reported periods notable for objects measured in kilometres, rather than only for small asteroids. The preprint’s authors infer that 491384 and 566130 have significant internal cohesion, allowing them to withstand the forces associated with such rapid rotation. The work is presented as a preprint, and the periods are reported approximately as five minutes.