Gullies inside Newton Crater - Terra Sirenum (Natural Colors; credits: NASA/MGS/MSSS)

Caption NASA originale:"Both pictures show gullies (gully--->plur.: gullies: "gole" o "crepacci scoscesi") on the walls of two different meteor impact craters that occur in Newton Basin in Sirenum Terra, Mars. This picture, showing gullies in a crater at 42.4°S, 158.2°W, exhibits patches (patch-->geol.: "placche" o "macchie") of wintertime frost on the crater wall and dark-toned sand dunes on the floor. Its resolution is 1,5 meters (5 feet) per pixel - objects the size of school buses can be resolved in the full size image. The gullies in these craters originate at a specific layer and may have formed by release of groundwater to the martian surface in geologically recent times".