Research Note

Vanishing torque from radiation pressure

¹ Department of Space Studies, Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, Colorado 80302, USA e-mail: davidn@boulder.swri.edu
² Observatório Nacional, R. Gal. José Cristino 77, 20921-400 Rio de Janeiro, Brazil
³ Institute of Astronomy, Charles University, V Holešovičkách 2, 18000, Prague 8, Czech Republic

Received: 31 July 2007
Accepted: 5 November 2007

Abstract

Context.Pioneering works on the effect of solar irradiation on the rotation of small objects in interplanetary space raised the possibility that the radiation pressure from solar photon absorption could modify the objects' spin states. Later numerical studies found that the torque from radiation pressure, when averaged over spin and orbital periods, vanished for all studied asteroid shape models.

Aims.We demonstrate that the average torque from radiation pressure vanishes for any surface shape deformation.

Methods.We have calculated the torque analytically. The main assumption of our calculation is that the object rotates around its principal axis of inertia.

Results.We show that the average torque vanishes for any surface shape deformation because the individual radiation-pressure contributions from configurations separated by π in orbital longitude cancel each other out.

Conclusions.Unlike the thermal radiation and reflection of solar photons from surface, which can produce important effects over planetary timescales, the radiation pressure cannot change asteroid rotation.