Fig. 1

Silicate and icy regolith in milligravity conditions. a A 1-km cliff on the 4 km diameter comet 67P/Churyumov–Gerasimenko imaged early in the ESA Rosetta mission (12/2014). Four-panel NAVCAM mosaic acquired from 20 km radius about the comet center. Surface gravity g~0.1 cm s⁻², so a leaping astronaut would land a half hour later at ~1 m s⁻¹, either into soft materials or a solid icy crust. Boulders at the cliff base are up to tens of meters diameter. Material is a combination of ices and amorphous volatiles and silicates and organics, in loose and cemented forms. b Ponded and buried craters, large and small boulders, and slumps and streaks on a region of 433 Eros, a ~20 km diameter potato-shaped rocky asteroid (NASA NEAR mission, JHUAPL/Cornell). Gravity g~0.6 cm s⁻². Image is 600 m across, and camera pixel scale is 2 m. Material is ordinary chondrite (mostly silicate) composition, ground down by small impacts to fine sizes