The color of Mars: Spectrophotometric measurements at the Pathfinder landing site

We calculate the color of the Martian sky and surface directly using the absolute calibration of the Mars Pathfinder (MPF) lander camera, which was observed to be stable during the mission. The measured colors of the Martian sky and surface at the Pathfinder site are identical to the Viking sites, i.e., a predominantly yellowish brown color with only subtle variations. These colors are distributed continuously and fall into five overlapping groups with distinct average colors and unique spatial characteristics: shadowed soil, soil, soil/rock mixtures, rock, and sky. We report that the primary difference between the sky color and the color of the rocks is due to a difference in brightness. Measurements of the sky color show that the sky reddens away from the Sun and toward the horizon and that the sky color varies with time of day and is reddest at local noon. We present a true color picture of the Martian surface and color enhancement techniques that increase image saturation, maximize color discriminability while preserving hue, and eliminate brightness variations while preserving the chromaticity of the scene. Although Mars has long been called the "red" planet, quantitative measurements of the surface color from telescopic and surface observations indicate a light to moderate yellowish brown color. The Pathfinder camera measurements presented here support the claim that the red planet is not red but indeed yellowish brown.