Fluvial erosion on Mars. Colour enhanced satellite image of the Candor Chasma region of the Valles Marineris canyon. It is thought that this canyon initially formed as the result of tectonic fracturing of the upper crust of Mars. The fractures, or joints, are visible as approximately vertical thin blue lines bordered by yellow areas (upper left to lower left). The yellow areas are halos, interpreted as areas of rock that have been chemically altered by fluid flowing through the joints. This image was obtained by the High Resolution Imaging Science Experiment (HiRise) camera on board the Mars Reconnaissance Orbiter, September 30th, 2006.