A laboratory study on sand grain impacts and their role in releasing fine dust into the Martian atmosphere

Abstract

<p>Dust in the Martian atmosphere is (under regular conditions) not larger than a few micrometers in diameter.<br />Liberation through impacts of sand grains during saltation is thought to be one source of this fine dust within <br />the atmosphere, as windspeeds usually do not exceed the threshold windspeed needed to pick up the highly <br />adhesive smallest particles directly.<br />We conducted a laboratory experiment to take a closer look at these saltating impacts and the resulting PSD of <br />the Ejecta on a microscopic scale: A small number of particles of about 200μm in diameter impacted a <br />simulated Martian soil (bimodal <em>Mars Global Simulant</em>). Impacts occurred at flat angles in fine vacuum <br />(10<sup>-2 </sup>mbar) with an impact speed of ∼ 1 m/s. The ejected dust was captured on adjacent <br />microscope slides and its size distribution was analyzed.<br />We find that the probability for ejection decreases dramatically with decreasing size. However, in spite of <br />strong adhesive forces, individual impacts still emit dust of 1μm and less. In fact, the probability <br />of ejecting dust of a given size can be characterized by a power law in the decade between 0.5μm <br />and 5μm (diameter).</p>