Surface processes in microgravity for landing and sampling site selection of asteroid missions—Suggestions for MarcoPolo-R

• Small asteroids’ surface properties are reviewed supporting next missions.
• Indicators of fresh material: albedo, colour and 1 μm band depth changes parallel.
• Smooth terrains are easy to navigate but sampling provide weathered material.
• MarcoPolo-R mission would identify formation of nanophase iron, amorphous particles.
• Surface age and transport process estimation will be supported by regolith density data.

Surface properties of small asteroids are reviewed in this work focusing on microgravity related processes in order to give constrains for targeting sample acquisition by next missions, especially for MarcoPolo-R proposed by ESA. Based on our current knowledge and the planned capabilities of this mission, good chance exists to get answers for the following basic questions. Formation method of nanophase iron and amorphous ingredients in the regolith could be determined, surface particle size and regolith density estimation would also be gained, and with extrapolation to the rest of the surface, knowledge on transport processes, ages and results of cratering under special gravity-strength regime will be improved.Searching for fresh material on asteroid surface in general requires sophisticated effort, as small craters often do not produce much ejecta in microgravity, but the bright annuli around them could be the result of local surface disturbance, while slopes often exhibit fresh material. To identify these locations high albedo, bluer colour and occasionally the depth of 1 μm absorption band could be useful as they often change parallel to each other. To identify the best area for sample acquisition addresses a strategic question: while smooth terrains with easy navigation and sample acquisition provide strongly weathered fine grains; steeper terrains give access to less weathered, material more representative for the whole asteroid, but navigation and mechanical sampling rise difficulties there.