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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.
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The periods given in this list are sourced from the Light Curve Data Base (LCDB), which contains light curve data for more than 15,000 bodies. Most minor planets have rotation periods between 2 and 20 hours. As of 2016, a group of approximately 600 bodies, typically measuring 1–20 kilometers in diameter, have periods of more than 100 hours or 4 1⁄6 days. Among the § Slowest rotators, there are currently 11 bodies with a period longer than 1000 hours. 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, therefor, can not be merely held together by self-gravity, but must be formed of a contiguous solid.
§ Potentially slow rotators have only an inaccurate period, estimated based on a fragmentary light curve 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.
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. However, in most cases the difference between these two different measures is not significant. This is the case for all main-belt asteroids, which account for 97.5% of all minor planets.
Slowest rotators
This list contains the slowest-rotating minor planets with periods of at least 1000 hours, or 41 2⁄3 days. See § Potentially slow rotators for minor planets with an insufficiently accurate period—that is, a LCDB quality code of less than 2.
Potentially slow rotators
Potentially slow rotators have their rotation period estimated based on a fragmentary light curve. They are listed separately from the more reliable results above, that have a quality code (U) of 2 or higher. The periods for potentially slow rotators may be completely wrong (U = 1), have no complete and conclusive result (U = n.a.), a large error margins of more than 30% (U = 2-), or anything in between.