Image 2-7
Martian Spiders

In this image from the Mars Reconnaissance Orbiter, unusual spider-shaped cracks can be seen in the surface of Mars. Scientists call them "araneiform," which means spider-like. They are believed to have been formed when frozen carbon dioxide gas sublimates, or turns directly from solid to gas. This occurs as the Martian winter ends and temperatures begin to increase. Frozen carbon dioxide trapped beneath the surface turns to gas and forms these fissures as it escapes back to the atmosphere.