The force arises because on a spinning asteroid, the dusk side
is warmer than the dawn side and emits more thermal photons, each photon carrying a small momentum.
For example, in analyzing 10,000 images, they found that more holes are produced over the dawn side of the earth than over the dusk side
. The down side faces the forward direction of the earth's orbit, so it shoudl sweep up more meteors, "just as a windshield wiper collects more drops in front of it than it does behind," says Sigwarth.
It would produce the Yarkovski effect wherein the dusk side
becomes warmer than the dawn side and cause the dusk side
to radiate more thermal protons that would cause the asteroid to alter its course.
Under these conditions, the Cluster data showed the waves on the dusk side
of the high-latitude magnetopause.