Mars Rover Investigates Possibility of Ancient Microbial Life
Riding with Robots writes "The robotic geologist Spirit, now scurrying to reach a safe haven before the harsh Martian winter sets in, has found signs that explorers say point to hot springs or fumaroles in the Red Planet's distant past. That possibility is not only interesting geologically, but potentially biologically, since those kinds of environments on Earth teem with microbial life. Meanwhile, on the other side of the planet, Opportunity continues its descent into a deep crater, where it has found other clues about the ancient waters of Mars."
It wasn't merely as insurance against a failure. It was also insurance against landing someplace utterly boring with one of them. Their landing method wasn't capable of getting into the places they knew were interesting, so they picked spots where they had a good chance of landing within driving distance of something that looked interesting from orbital images.
They originally thought they struck out with Spirit. Sure they had a few rocks to grind on, but they were all ejecta from the lava plains. Basalt isn't very interesting if you're looking for evidence of past water.
However, as the mission wore on, they realized they would probably have time to drive to Columbia Hills, which they in fact accomplished, and that turned out to be a trove of information. These possible fumeroles are on the far side of Columbia Hills from where they landed.
Opportunity was just lucky from the beginning. Sucker landed right inside a crater. The Spirit team was more than a little jealous.