The Opportunity Rover, one of the most successful explorers in history, has added another remarkable discovery to its résumé. Opportunity has found a type of clay that is deposited in water – not just any water, but water with the right chemistry for our kind of life. In the words of Project Manager Steve Squyres, "This is water you could drink."
What's the big deal? Haven't our intrepid Mars rovers already found lots of evidence for ancient Martian water? Yes, they have. But this discovery is different.
Water is one of the weirdest substances in the universe. One of the things that makes water weird is that it dissolves nearly everything it touches. In fact, when you pour water into a glass, the water instantly starts to dissolve the glass itself (just a little), so that there are tiny dissolved bits of glass in the water you drink. This property of water makes it fantastic stuff for life, but also makes it easy to contaminate and pollute water to the point where life can have problems.
In particular, water can become very basic (think oven cleaner) or very acidic (think stomach acid). Neither of these conditions is particularly suitable for life (though Earth life is so varied that some organisms have actually adapted to extremely acidic or basic conditions). Water does this by dissolving whatever substances it happens to touch.
Most water discoveries so far on Mars have indicated extremely acidic water, the kind that is great for dissolving rock, but not so great for quenching your thirst. The latest Opportunity discovery, however, is of a type of clay that is deposited only in neutral water. This water, neither acidic nor basic, is water we humans could actually have drunk.
The discovery doesn't prove that life once existed on Mars, but it brings us a lot closer to reconstructing an ancient environment where our kind of life could have existed. Pretty exciting stuff!
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