December 12, 2007 8:31 AM PST
Scientists theorize that the shiny patch, accidentally uncovered when one of Spirit's wheels spun, is made of nearly pure silica, which is the main ingredient in window glass. Scientists believe its high concentration indicates that it was formed by hot springs or a fumarole, in which acidic steam rises through cracks.
The importance of this discovery, according to NASA, is that, on Earth, these types of environments are teeming with life--raising hopes for finding microbes on Mars. On Earth, fumaroles are found in Hawaii and Iceland.
Photo by NASA/JPL/Cornell
