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Ray's Clays

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Ray Arvidson, a geologist from Washington University, nearly jumped for joy when he discovered a mineral named, "Kaolinite" in some clays in the FIDO landing site area. If he would have found the same mineral in mud-like material on Mars, he would have "run down the street waving the papers!"

Ray Arvidson, Meredith Berwick, Ed Guiness

As far as we know it, in order to have life, a planet must have water. Kaolinite is a mineral that only forms in the presence of water, so if Ray and the Mars Exploration Rover team were to find this mineral in clay on Mars, it would confirm that liquid water once flowed on Mars, which opens up a wider possibility that life may have existed there at one time.

First of all, scientists were excited to see material on the ground that looked like cracked clay (or mud) because the texture of clay is fragile and the cracks don't last long, meaning recent storm activity must have taken place. Features like this are formed by rain, as sediments travel down a valley. As storms subside, fine grains collect together in a "slack." Slack is a term geologists use for mud puddles which form after rains slow down. "Just like a slacker is slow, this "slack" forms when wet material bonds with fine, slow moving grains of soil."

The cracks and texture of the soil provide evidence that some "liquid" slowed down here long enough to create clay. Now, the challenge was to discover what kind of liquid formed the clay. Was it water?

When clays get wet, they expand, and when the liquid evaporates, the clays shrink and crack as one can see in this image. These cracks become was Ray calls, "Mother Nature's collection bowls." The cracks contain minerals that were previously stripped from rocks upstream and flowed down the valley with the liquid, coming to rest deep within the clay. Ray and the science team thus decided to turn on the robotic geologists' infrared instruments to look for the release of energy signals given off by specific minerals.

After running through over 100 types of mineral spectra, the soil team found a "double-dip" fingerprint match to kaolinite in the cracks of the clay (see spectra chart). Since kaolinite only forms in the presence of water, these clays must have been formed by water. (The scientists had predicted the mineral would be kaolinite because the clays were a white color and kaolinite is a white mineral. Kaolinite is the mineral that makes both paper and Kaopectate white!)

Even more exciting is the new hypothesis that there must be a bigger source of kaolinite upstream of this location. Now the scientists want to go find the original source of the kaolinite to see if the water that flowed in this area came from an ancient ocean or out of ancient volcanoes.

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Last Updated: 17 August 2002

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