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The Yarkovsky Effect - Part 1 of 7

On Wed, 24 Mar 1999, Julia kindly wrote:

So it turns out having to do with thermo-dynamics and other influencing
factors and maybe not as anomalous as previously thought, depending on
size, density, location, velocity, rotation, etc. of asteroids.

And Ron kindly answered:

Yes, it applies to all small asteroids. However, Jupiter's gravitational
effect on the asteroid belt applies as well, and is the bigger factor of
the two. If you are doing long term calculations of an asteroid's orbit,
you are going to have to incorporate the Yarkovksy effect. For
short-term calculations, the Yarkovksy effect is so small it can be
ignored.



W.K. Hartmann et al. (1999) Reviewing the Yarkovsky effect: New
light on the delivery of stone and iron meteorites from the asteroid
belt (MAPS 34, 1999, A161-A167, excerpts + summary):

Abstract

Two variants cause drifts in orbital elements, notably semimajor axes.
The "classic" or "diurnal" Yarkovsky effect is associated with diurnal
rotation at low obliquity.
More recently, a "seasonal" effect has also been described, associated
with high obliquity.
Studies of these Yarkovsky effects combined with studies of resonance
effects help clarify meteorite delivery.
If there were no Yarkovsky drift, asteroid fragments could reach a
resonance only if produced very near that resonance.
However, objects in resonances typically reach Earth-crossing orbits
within a few million years, which is inconsistent with stone meteorites'
cosmic-ray exposure (CRE) ages (5-50 Ma) and iron meteorites' CRE ages
(100-1000 Ma).
Large objects in the asteroid belt are "fixed" in semimajor axis, but
bodies up to 100 m in diameter are in a constant state of mixing and
flow, especially if the thermal conductivity of their surface layers is
low.
Small asteroid fragments may reach the resonances after long periods of
drift in the main belt.

Yarkovsky drift effects, combined with resonance effects, appear to
explain many meteorite properties, including:

(1) the long CRE ages of iron meteorites (due to extensive drift
lifetimes in the belt);
(2) iron meteorites' sampling of numerous parent bodies;
(3) the shorter CRE ages of most stone meteorites (due to faster drift,
coupled with weaker  strength and more rapid collisional erosion
(4) the abundance of falls from discrete impact events near resonances,
such as the 8 Ma CRE  age of chondrites.

Other consequences include:

- the delivery of meteorite parent bodies to resonances is enhanced
- proportions of stone and iron meteorites delivered to Earth may be
different from the  proportions at the same sizes left in the belt
- the proportions at the same sizes left in the belt may differ from the
ratio produced in  asteroidal collisions
-  Rabinowitz’s 10-100 m objects may be preferentially delivered to
near-Earth space
- the delivery of C-class fragments from the outer belt may be
inhibited, compared to classes  in other parts of the belt.


Best wishes,

Bernd

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