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Poynting-Robertson Effect



The Poynting Robertson effect actually _decelerates_ dust grains and
smallish meteoroids (10^-3 cm up to about 1 cm in diameter) in solar orbit.
It originates because in the rest frame of the orbiting object sunlight
actually arrives with a small component of its Poynting vector anti-parallel
to the meteoroid's velocity vector. This has the effect of making the
object spiral inward to eventual destruction in the Sun. For smaller
objects the dominant radiation pressure effect is to blow them out of the
solar system.

Interestingly enough, for objects ranging from a few centimeters up to a few
tens of meters there is another effect of radiation pressure called the
Yarkovsky effect. In this case the thermal radiation from the meteoroid
acts like a reaction thruster. As the object rotates the re-radiated energy
can alter its orbit substantially. Depending on rotation rate and whether
its rotation is prograde or retrograde the object can spiral in or out. For
stuff larger than kilometer scale there is negligible radiation effect. For
stuff smaller than micron scale the dominant non-gravitational force is ram
pressure from the solar wind.

George Spagna **********************************************
Department of Physics * *
Randolph-Macon College * And so some day, *
P.O. Box 5005 * The mighty ramparts of the mighty universe *
Ashland, VA 23005-5505 * Ringed round with hostile force *
* Will yield and face decay *
phone: (804) 752-7344 * and come crumbling to ruin. *
FAX: (804) 752-4724 * - Lucretius, De Rerum Natura *
e-mail: gspagna@rmc.edu **********************************************
URL: www.rmc.edu/~gspagna/gspagna.html