In looking back on the months of Mars exploration, what is the most striking, surprising new view of Mars obtained by the rovers?
"That's hard to say this early in the game. I think it's going to take a long time for the science community to fully digest our results," said Steve Squyres of Cornell University in Ithaca, New York and principal investigator for the Mars Exploration Rover project.
But Squyres added: "What's emerging to me is a picture of Mars as a planet that's made of basaltic rock, and with groundwater that's dilute sulfuric acid. The acid interacts with the rock, dissolving things out of it, and then can evaporate away and leave interesting sulfate salts behind. When you have a little interaction and a little evaporation, you get the kind of deposits -- like a little bit of magnesium sulfate salt in the soil -- that we see at Gusev. When you have a lot of interaction and a lot of evaporation, you get the kind of sulfate-rich evaporate beds we see at Meridiani."
Taking this into consideration, the life on Mars issue, Squyres said, means grappling with a key notion. "I think that we've got to start considering how easy it might or might not be for life to take hold in this kind of sulfur-rich, low-pH [measure of acidity] environment."
I'm not sure anyone knew how bad it actually could be. When asked about the possibility of extremophiles, Knoll didn't deny the possibility but suggested that extremophiles on Earth depended on inputs of nutrients from neighbouring, more pleasant ecosystems.