  The most likely cause of levitation of dust above the surface of
atmosphereless planets is the electrostatic mechanism. However, the crucial
problem in the explanation of this effect is a determination of the reason why
a large electric charge (units or even dozens of elementary charges) required
for take-off can be accumulated on the smallest dust particles. Due to the
photoeffect the charge of such value could be easily accumulated on a solitary
dust particle, but if a dust particle has not yet taken off, the average value
of its charge is several orders of magnitude lower because of the extremely low
charge density on the planet's surface. The paper shows that surface charge
density is really small only for averaging over regions of macroscopic size,
and on a submicron scale the surface appear to be a collection of chaotic
"spots" with charges of different signs. The positively charged "spots" are
only slightly larger than the negatively charged spots, which explains the
small value of the charge density averaged over macroscopic regions. "Spots"
arise due to fluctuations in the fluxes of the photoelectrons taking off and
falling back the surface, and the charge density inside the "spots" is
sufficient to allow a takeoff of particles with the dimensions less than or on
the order of 0.1 micron in the field of a double layer.
