  In this work we present laboratory measurements on the reduction of the
threshold friction velocity necessary for lifting dust if the dust bed is
illuminated. Insolation of a porous soil establishes a temperature gradient. At
low ambient pressure this gradient leads to thermal creep gas flow within the
soil. This flow leads to a sub-surface overpressure which supports lift imposed
by wind. The wind tunnel was run with Mojave Mars Simulant and air at 3, 6 and
9 mbar, to cover most of the pressure range at martian surface levels. Our
first measurements imply that the insolation of the martian surface can reduce
the entrainment threshold velocity between 4 % and 19 % for the conditions
sampled with our experiments. An insolation activated soil might therefore
provide additional support for aeolian particle transport at low wind speeds.
