Discovery of 2 km ultra-fast rotating asteroid in Rubin DP2 catalog via varying Fourier order method

Time-resolved photometry from large surveys can produce rotation periods for huge numbers of asteroids, but only if each period's reliability is assessed automatically, since sparse and irregular sampling generates many false periodogram minima.

The authors present an improved method that determines asteroid rotation periods using a Fourier series whose order is chosen individually for each object. This offers substantial advantages over lower-order methods, especially when a unique spin period cannot be reliably determined; in those cases the method reports the set of alternative periods along with corresponding probability estimates.

Applying the method to the NSF-DOE Vera C. Rubin Observatory Data Preview 2 (DP2) catalog of solar system objects, they derived reliable periods for a large sample of asteroids. Among them they found 66 super-fast rotators, spinning faster than the classical 2.2 h spin barrier. Two stand out: asteroids 491384 and 566130 are both larger than 2 km yet complete a full rotation in only about five minutes.

To survive such a fast spin, these bodies must have significant internal cohesion. At a diameter of about 2.5 km, asteroid 491384 is the largest ultra-fast rotator known so far.