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[13.04] The Yarkovsky Effect on Regolith-Covered Bodies

J.N. Spitale, R. Greenberg (LPL)

Our numerical solution to the heat equation allows us to evaluate orbital element changes for small, rocky bodies caused by the Yarkovsky effect over a wide range of parameters. We have corroborated previous calculations and extended the theory to very large eccentricities and arbitrary spin states[1]. We now investigate the Yarkovsky effect throughout a similar parameter space for 10- and 100m bodies possessing insulating surface layers (e.g. regolith) of 0.01 and 0.001 body radii.

For bodies on orbits with eccentricities less than about 0.7, the pure seasonal extreme of the Yarkovsky effect (on semimajor axis) is substantially inhibited (10 or more times slower) by the addition of a regolith. This result appears to contradict that of [2]. For bodies on orbits with very high eccentricity, this effect is generally weaker (not always much weaker) than for the regolith-free case, but has a complicated dependence on the semimajor axis (da/dt varies drastically with a).

In [1], we observed that da/dt associated with the diurnal component of the Yarkovsky effect grows with e and, under some circumstances, can be very fast (up to 50 times faster than for e=0) for high-eccentricity orbits. The addition of a regolith can cause significantly faster da/dt for orbits with eccentricities less than about 0.7, but not much change in the strength of the effect for higher eccentricity orbits. Similar to the seasonal case, the behavior can be fairly complicated for these high-eccentricity orbits.

Also, the Yarkovsky effect can cause the eccentricity and inclination of orbits of small, regolith-free bodies to increase or decrease quite rapidly, depending on the spin axis orientation, though such effects might be averaged away if the spin axis reorients rapidly enough.

The Yarkovsky effect depends very strongly on the amount of regolith covering a body.

References:

[1] Spitale, J. N. and R. Greenberg {\em Icarus} in press

[2] Vokrouhlický, D. and M. Broz (1999) {\em A&A} \textbf{350}, 1079--1084