Megan Elwood Madden, of Jacksonville, Ill., a graduate student in geosciences, along with Robert Bodnar, University Distinguished Professor and Clifton C. Garvin Professor of Geosciences, and Donald Rimstidt, professor of geosciences, all in the College of Science, published "Jarosite as an indicator of water-limited chemical weathering on Mars" in the Oct. 14 issue of Nature according to a press release from Nature.

NASA's Mars Rover Opportunity recently found the mineral jarosite and possibly gypsum on Mars' surface, further adding to the speculation that water existed there in the past because those minerals "generally form in a wet environment," according to a Nature news release.

It was already well known from previous Mars research and meteorites that basalt is likely a common rock type on Mars, Elwood Madden said. Scientists are interested in the history of water on Mars since life as we know it cannot survive without liquid water. Ice can be found on Mars today; however, liquid water likely froze or evaporated some time in the past.

Using a computer-modeling program that uses thermodynamic data to determine the types of minerals that form from reactions between rocks and water, Elwood Madden looked at the way basalts weather, or react with water, under the conditions found on Mars and used the results to interpret how jarosite and gypsum might have formed. "We predicted jarosite likely did form from a reaction of basalt with liquid water," Madden said.

"On Earth, jarosite forms in acid mine drainage environments as sulphide minerals oxidize -- it has been found in Idaho or California, for example. It also forms while volcanic rocks are being altered by acidic, sulphur-rich fluids near volcanic vents. As such, jarosite formation is thought to need a wet, oxidizing and acidic environment."

However, it is preserved only in arid regions. The reason, Elwood Madden and Rimstidt said, is that jarosite forms when only a small amount of reaction has occurred and completely decomposes if more water is available. "This shows that the reaction on Mars ran out of water," Elwood Madden said.

"Either there was not enough water to begin with or it disappeared quickly," Rimstidt said.

Elwood Madden, Bodnar, and Rimstidt showed "that the water in which the minerals formed either evaporated or soaked into the ground after a short time," according to Nature.

Because water is important for life, the discovery could have implications of how long water was present on Mars and the likelihood of finding living organisms there now. "There's probably no likelihood of living organisms today, but we can't say there wasn't enough water a long time ago," Rimstidt said.

As to how much water was on Mars, the researchers do not know if there was a great deal for a short time or a little for a longer period. However, they can say there was a geologically short window in which liquid water was present, suggesting there also was a limited time period when conditions may have been hospitable for life, Rimstidt said.

The researchers will present the results of their work in November at the Geological Society of America meeting in Denver.

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