Evidence for recent groundwater seepage and surface runoff on Mars

Relatively young Landforms on Mars, seen in high-resolution images acquired by the Mars Global Surveyor Mars Orbiter Camera since March 1999, suggest the presence of sources of liquid water at shallow depths beneath the marti an surface. Found at middle and high martian latitudes (particularly in the southern hemisphere), gullies within the walls of a very small number of i mpact craters, south polar pits, and two of the Larger martian valleys disp lay geomorphic features that can be explained by processes associated with groundwater seepage and surface runoff. The relative youth of the landforms is indicated by the superposition of the gullies on otherwise geologically young surfaces and by the absence of superimposed Landforms or cross-cutti ng features, including impact craters, small polygons, and eolian dunes. Th e limited size and geographic distribution of the features argue for constr ained source reservoirs.