This image shows a geological feature know as recurring slope lineae on the surface of Mars. These flows, which occur seasonally, are suspected by NASA to be the result of seeping water.
The lineae tend to occur around bedrock cliffs and rocky outcrops. The ones in this image are situated on the edge of the Hale Crater, and they stand out more than usual because of their unusually reddish colour. NASA suggests that could be because they contain oxidised iron compounds, like rust — a tell-tale sign of the presence of water. This image was captured by the HiRISE satellite. [NASA]