关于这张图
This enhanced-color image from NASA Mars Reconnaissance Orbiter shows gullies in the northern wall of an unnamed crater in Utopia Planitia. The banked, sinuous shape of the gully channels suggest that water was involved in their formation. The source of this water however is a subject of debate. Hypotheses include melting of snow or near-surface ground ice. Other features also suggest the past (and possibly present) presence of snow or ground ice in this region. For example, the "mantle" deposit on the crater wall displays polygonal fractures. Polygons on Earth are associated with periglacial…
