Lifting Dust on Mars by Greenhouse Effects and Thermophoresis

Introduction: Dust is continuously lifted from the Martian surface and put into atmospheric suspension. This is well visible during dust devil activity [1] and planet encircling dust storms [2]. The mechanism for the atmospheric dust entrainment has been debated for a long time. Wind stress can easily put dust into suspension under Earth conditions, i.e. at ~1000 mbar surface pressure. In principle the same mechanism is able to lift particles from the Martian ground as well and will do so occasionally. However, wind speeds have to be much higher than on Earth due to the low atmospheric pressure of 1 to 10 mbar [3]. Wind speeds necessary to initiate dust lift-off depend on the atmospheric pressure and have to be much larger than 30 m/s on Mars at the highest pressures. These speeds are not available continuously. While gas drag decreases in strength with decreasing pressure, thermophoretic forces on dust particles increase in strength and are especially strong in the low atmospheric pressure range given on Mars. The lift provided by thermophoresis might facilitate the entrainment of dust from the surface.