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.
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.
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