**DPS Pasadena Meeting 2000, 23-27 October 2000**

*Session 13. Asteroids II - Discovery and Dynamics*

Oral, Chairs: W. Merline, J. Burns, Tuesday, 2000/10/24, 8:30-10:00am, C106
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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

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