Yarkovsky effect

In physics, the Yarkovsky effect is a force felt by a body caused by the momentum carried away by the thermal photons that it emits. It was discovered by a Russian engineer named I.O. Yarkovsky a century ago. This effect causes perturbations in the orbit of asteroids, and is probably important in the transport of asteroids from the main belt to the inner solar system.

It is very hard to predict the exact impact that the Yarkovsky effect will have on a specific asteroid's orbit, however, due to the fact that it is affected by a great many variables that are hard to account for with limited observational information. The Yarkovsky effect depends upon the shape of the asteroid, its orientation, its rotation rate, and its albedo; these factors are further complicated by the effects of shadowing and thermal "reillumination", which are not relevant for bodies with convex shapes, and the effect of directly reflected sunlight (radiation pressure), which is usually neglected for spherical bodies with uniform albedo.

Even for the simple case of the pure seasonal Yarkovsky effect on a spherical body in a circular orbit with 90° obliquity, semimajor changes could differ by as much as a factor of two between cases with uniform albedo and cases with a strong north/south albedo asymmetry. For higher eccentricity, greater differences are possible. Depending on the orbit and spin axis, the Yarkovsky semimajor axis change may be reversed simply by changing from a spherical to a nonspherical shape.