Regolith is the layer of rocky or icy debris, sand, and dust made by meteoritic impact that forms the uppermost surface of planets, satellites and asteroids. It is a possible construction material in the form of sintered regolith bricks. Loose regolith may also be used as a radiation shield.
Landscapes with regolith formation have been found that look like they were shaped by the flow of water. Thoses formations were probably created by "gas-supported density flows". 
 Open Issues
- How radioactive is regolith?
- What are the compositions of the regolith near possible settlement sites?