[31.04] Asteroid Spin States Produced by Thermal Torques

DPS 35th Meeting, 1-6 September 2003
Session 31. Asteroid Dynamics I
Oral, Chairs: W. F. Bottke, Jr. and J. S. Stuart, Friday, September 5, 2003, 10:30am-12:00noon, DeAnza I-II

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[31.04] Asteroid Spin States Produced by Thermal Torques

D. Nesvorny (Southwest Research Institute), D. Vokrouhlický (Institute of Astronomy, Charles University), W. F. Bottke (Southwest Research Institute)

Recent observations suggest that physical phenomena other than collisions determine the spin states of small main-belt asteroids. Indeed, diameter D < 40 km asteroids in the Koronis family have peculiar rotation rates and preferentially aligned spin axes (Slivan, 2002, Nature 419, 49). Here we show that that these spin states can be naturally explained by accounting for thermal (YORP) torques (Rubincam 2000, Icarus 148, 2), which modify asteroid spin states over time, and in some cases, allow them to become trapped in spin-orbit resonances. We predict that many D < 40 km main-belt asteroids evolved by YORP torques to have either long (P > 7 hours) or short (P < 3 hours) spin periods and preferential obliquities of 0, 55, or 180 degrees. This prognosis is testable by lightcurve observations.

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