Why Mars Is Red

If we feel any disappointment at the loss of our cherished Martian canals, at least we can still enjoy the image of the “angry red planet.” Yet the source of the reddish hue is not the bloody spirit of the Roman god of war, but simple iron ore. The Martian surface contains large amounts of iron oxide, red and rusting. As Viking 1 and Mars Pathfinder images revealed, even the Martian sky takes on a rust-pink tinge during seasonal dust storms.
The dust is blown about by winds that kick up in the Martian summer. These winds play a prominent role on Mars, forming vast dunes and streaking craters. An especially large dune is found around the north polar cap.