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Pasadena, CA. — NASA’s news Tuesday that the Meridiani Planum landing site on Mars was once “drenched in water” qualifies as a genuine “ah-ha moment,” said University of Tennessee geologist Hap McSween.

“It’s a major discovery. I’ve always believed water could be there. I just didn’t quite believe that we were going to be able to answer this question so unambiguously,” he said Tuesday from NASA’s Jet Propulsion Laboratory in Pasadena, Ca. “Mars has always been a hard place to work, but the Meridiani Planum has been very kind to us.”

McSween is a co-investigator and science team member on the current Mars Exploration Rover Mission. He is at JPL with UT assistant professor Jeff Moersch, who is also a co-investigator, and UT senior Sandra Ciccollela. UT graduate students Keith Milam, Karen Stockstill and Livio Tornabene have also spent time at JPL since January helping to analyze data from the rovers.

The discovery of past water does not automatically suggest the presence of life, McSween said.

“The presence of water does not always equal life, but it allows you to contemplate it,” he said. “Life as we know it requires liquid water. This discovery also tells us that the environment was warm enough for the water to be liquid. Now, it’s worth looking.

“There is almost certainly still water on Mars underground, but liquid water is not stable anywhere on the surface of Mars today. We’re looking at something that happened in the distant past, when Mars was a different place than it is now, a warmer, wetter planet.”

McSween was involved in selecting the rock outcroppings to be explored by Opportunity last week. Now, he said, he and Moersch are focused on the Gusev crater and the work of the Spirit rover.

“We are grinding into a rock that looks like lava, which will tell us about the composition of the martian crust. The meteorites we have examined in the past are different from the rocks we are examining now.

“We are trying to reconstruct the geologic history of the whole planet. We’ve only had samples from one period of time before. Now we have samples we can study that are much older, and are giving us a different answer.”