An insolation activated dust layer on Mars

•The Illumination of the dusty surface of Mars leads to a gas flow through the soil.•A pressure gradient within the top layer supports dust lift on Mars.•Experiments showed the thickness of the activated layer: 100–200μm.•Threshold wind speeds for saltation can be reduced by about 10%. The illuminated dusty surface of Mars acts like a gas pump. It is driven by thermal creep at low pressure within the soil. In the top soil layer this gas flow has to be sustained by a pressure gradient. This is equivalent to a lifting force on the dust grains. The top layer is therefore under tension which reduces the threshold wind speed for saltation. We carried out laboratory experiments to quantify the thickness of this activated layer. We use basalt with an average particle size of 67μm. We find a depth of the active layer of 100–200μm. Scaled to Mars the activation will reduce threshold wind speeds for saltation by about 10%.