Slow Rotating Asteroids: A Long Day's Journey Into Night (Abstract)

Volume 37 number 2 (2009)

Brian D. Warner

Abstract

(Abstract only) While there is no formal definition of a “slow rotator” among asteroids, anything with a period of at least 24 hours can be considered to be at least at the fast end of the group. These objects are of particular interest to those studying the evolution and dynamics of the asteroids within the solar system for several reasons. Most important among them is to generalize theories regarding the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect, which is the thermal re-radiation of sunlight that can not only affect the orientation of an asteroid’s spin axis but its rate of rotation as well. In those cases where the spin rate is decreased, an asteroid can eventually be sent into a state of “tumbling” (NPAR—non-principal axis rotation) that can last for millions of years. However, not all slow rotating asteroids appear to be tumbling. This is not expected and so careful studies of these objects are needed to determine if this is really the case or if the tumbling has reached a condition where the secondary frequency—the precession of the spin axis—has been reduced to near zero. Furthermore, there appears to be an excess of slow rotators among the Near-Earth asteroids (NEA) and inner main-belt populations. Determining whether or not this is true among the broader population of asteroids is also vital to understanding the forces at work among the asteroids.