List of slow rotators (minor planets)

This is a list of slow rotators—minor planets that have an exceptionally long rotation period. This period, typically given in hours, and sometimes called rotation rate or spin rate, is a fundamental standard physical property for minor planets. In recent years, the periods of many thousands of bodies have been obtained from photometric and, to a lesser extent, radiometric observations.

This plot shows the distribution of rotation periods for 15,000 minor planets, plotted against their diameters. Most bodies have a period between 2 and 20 hours.[1][lower-alpha 1]

The periods given in this list are sourced from the Light Curve Data Base (LCDB),[2] which contains lightcurve data for more than 15,000 bodies. Most minor planets have rotation periods between 2 and 20 hours.[1][3] As of 2019, a group of approximately 650 bodies, typically measuring 1–20 kilometers in diameter, have periods of more than 100 hours or 41⁄6 days. Among the slowest rotators, there are currently 15 bodies with a period longer than 1000 hours.[1] According to the Minor Planet Center, the sharp lower limit of approximately 2.2 hours is due to the fact that most smaller bodies are thought to be rubble piles – conglomerations of smaller pieces, loosely coalesced under the influence of gravity – that fly apart if the period is shorter than this limit. The few minor planets rotating faster than 2.2 hours, therefore, can not be merely held together by self-gravity, but must be formed of a contiguous solid.[3]

Potentially slow rotators have only an inaccurate period, estimated based on a fragmentary lightcurve and inconclusive measurement. They are listed separately from the more precise periods, which have a LCDB quality code, U, of 2 or 3 (unambiguous result). The periods for potentially slow rotators may be completely wrong (U = 1), have no complete and conclusive result (U = n.a.), or large error margins of more than 30% (U = 2−). A trailing plus sign (+) or minus sign (–) indicate slightly better or worse quality, respectively, than the unsigned value.[4]

As with orbital periods, a rotational period can be sidereal or synodic to describe a full rotation with respect to the fixed stars (sidereal) and Sun (synodic), respectively. In most cases, the periods given in this list are synodic, not sidereal.[5][6] However, in most cases the difference between these two different measures is not significant.[6] This is the case for all main-belt asteroids, which account for 97.5% of all minor planets.