Scientists have found signs that water may once have gurgled up
through the Martian soil in hydrothermal vents similar to those
in Yellowstone National Park. The site of these proposed vents
could possibly contain preserved traces of ancient Martian life,
scientists say. That assumes, of course, that life might once
have existed on Mars. No firm evidence for that idea has ever
been found, however. The vents evidence comes from NASA's Mars
Exploration Rover Spirit. The robotic explorer found deposits of
pure silica, a form of the element silicon that occurs when hot
water reacts with rocks (quartz is a pure silica), in Mars'
Gusev Crater in 2007. The discovery was announced briefly at the
time, but scientists have now had time to fully analyze the
deposits. The results are detailed in the May 23 issue of the
journal Science. The silica was found when Spirit was exploring
the Columbia Hills, which rise 300 feet from the middle of the
flat lava plain that fills Gusev Crater. Scientists were
uncertain about just