DURING SOUTHERN WINTER, carbon dioxide gas condenses onto the polar cap as a thin slab of translucent CO2 ice. When the Sun rises in spring, the ice sublimates from the bottom of the layer, and the growing gas pressure lifts the slab off the ground. Gas then breaks through the slab in places, erupting in jets that carry dust scavenged from under the slab. The jets leave dark dust marks on the surface of the ice cap. TES made polar cap temperature measurements that led to the development of the model for the jets. Click on the image to download a larger version (5.6 MB). Arizona State University/Ron Miller