Cold jets in the Martian polar caps

Mars seasonal polar caps display dark ice, local darker spots, aligned elongate patches, and radially dendritic forms that reverse albedo contrast. The unexpected variety and sequence of these features are explained on the basis of processes involving CO2, dust, sand, and H2O. These processes are largely related to the atmosphere being near its saturation temperature, and they have few terrestrial analogies. In the simplest case the ∼1 m thick seasonal cap, initially dusty, cleans itself and becomes translucent after sunrise and is impermeable over extensive regions except for local vents. The slab ice sublimates at the base and is levitated on high‐pressure gas, causing humidity exchange with deeper layers; subslab gas converging toward the vents erodes channels in the soil and ejects this material in high‐velocity jets. Recent spectral observations indicate great variety in the details.