LEE%SU-STAR@sri-unix.UUCP (06/09/84)
Could you explain the radiation drag mechanism?. I don't quite see how it causes orbital decay, although it is clear that such an effect depends on the surface area/mass ratio of theorbiting particle. Emilio P. Calius Stanford U. ------
REM%MIT-MC@sri-unix.UUCP (06/12/84)
From: Robert Elton Maas <REM @ MIT-MC>
Date: 8 Jun 1984 2249-PDT
From: LEE at SU-STAR
Could you explain the radiation drag mechanism?.
Here's my quick attempt: Radiation is doppler-shifted depending on
direction of motion of particle. The difference of energy&momentum
between the front and back of the particle causes it to slow down in
its orbit, causing it to fall into the object it is orbiting (Vega in
this case). For average particles area is proportioal to diameter
squared whereas mass to diameter cubed, and both lightpressure and
gravity are proportional to distance-from-star to the minus 2 power,
so very tiny particles have more area*lightpressure than mass*gravity,
thus are thrown out to deep space by lightpressure even if not
orbiting, but slightly-larger particles have more mass*gravity than
area*lightpressure, so they eventually fall inward after they stop
orbiting. Very large particles take a very long time before they
significantly slow down orbiting, so in their case lightpressure vs
gravity is moot. But tiny and medium-small particles are removed from
orbit, to deep space and into the star respectively, after just a
short time in the life of a star.