DPS 2001 meeting, November 2001
Session 54. Asteroid Discovery and Dynamics II
Oral, Chairs: D. Durda, P. Michel, Saturday, December 1, 2001, 11:05am-12:35pm, Regency E

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[54.03] The Yarkovsky effect: Role of asteroid shape and albedo distribution

J.N. Spitale, R. Greenberg (University of Arizona)

The Yarkovsky effect is a recoil felt by a body in response to the momentum carried away by the thermal photons that it emits. Its effect on the orbital elements of asteroids has been investigated by many authors for ideal bodies, that is, spherical bodies with uniform albedo and thermal properties. The results of those studies show that the Yarkovsky effect is probably important in the transport of asteroids from the main belt to the inner solar system.

More realistic calculations can yield Yarkovsky perturbations for specific solar system bodies. Such results could lead to more precise NEA ephemerides, which would be important for radar observations, direct observations of Yarkovsky displacements, and NEA hazard detection (and perhaps mitigation). To develop such a tool, we use the finite-difference approach (Spitale and Greenberg; Icarus 149:222), suitably modified to study bodies with nonspherical shapes and nonuniform albedo. The effects of shadowing and thermal ``reillumination'', which are not relevant for bodies with convex shapes, are included. The effect of directly reflected sunlight, which is usually neglected for spherical bodies with uniform albedo, is also included.

Even for the simple case of the pure seasonal Yarkovsky effect on a spherical body on a circular orbit with 90o 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 and are investigated using the numerical approach. Depending on the orbit and spin axis, Yarkovsky semimajor axis evolution may be reversed by changing from a spherical to a nonspherical shape.

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