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March 4, 2004 Sorry it's been so long since I've done one of these updates! The story of the Meridiani outcrop has grown very interesting, and it has taken up much of my time and attention.
By now you've probably heard that we think the rock that makes up this outcrop was once pretty well soaked in liquid water. There are four lines of evidence that support this idea. One is that we now think it's pretty likely that the little round things in the outcrop (the "blueberries") are what geologists call "concretions". They seem to be different in composition from the stuff in which they're embedded, they don't deform the layers around them, they're not concentrated along layers, and we sometimes see layers running through them... all of which are consistent with the idea that they're concretions. And if that's what they are, then they point to water, since concretions form when minerals are precipitated from groundwater.
The second piece of evidence is some weird little holes that are shot through many parts of the outcrop. The holes are tabular in shape, and they look just like what happens when crystals of certain minerals (gypsum could be one example) form from liquid water in a rock. The crystals grow in tabular shapes, and then later they either dissolve or erode away, leaving funny chicken-scratch looking holes behind. You might be able to come up with some other explanation for these things, but they're awfully darn similar to features found in rocks on Earth where this has happened. It seems to be the most likely explanation.
The third piece of evidence is that there is a huge amount of sulfur in this rock. There's so much sulfur that we think there has to be a lot of some kind of sulfate salt in the rock, which is very hard to account for unless water was involved.
And finally, we see a mineral called jarosite in this rock, which is an iron sulfate hydrate. There's a lot of jarosite there, and jarosite is a mineral that requires water for its formation.
So water once flowed through these rocks. It changed their
texture and their chemistry, and it left behind the clues that we've been able to read. It's a nice conclusion, and we feel pretty confident about it.
The really cool thing here, of course, is that a groundwater environment like this would have been suitable for some simple forms of microbial life. That doesn't mean life was there, of course! But we flew this mission because we wanted to find out if Mars ever had habitable environments. And the answer, we now believe, is that it did.
After we announced all this to the world yesterday, I had a
reporter ask me if this finding meant "mission accomplished". My answer was, effectively, "yes and no". On the one hand, we set out to learn something about Mars, and we've done it. If both rovers died tomorrow, heaven forbid, I think this mission now would always be thought of as a success.
On the other hand, we've still got two very healthy rovers on the surface of Mars, and a lot more work to do. At Gusev, the best stuff may lie ahead, either in Bonneville crater or off towards the Columbia Hills. And at Meridiani, who knows what wonders lie outside this little crater that we landed in. In some sense, I'm not going to feel like we've really accomplished our mission until we've learned everything about Mars that we can possibly learn with these two wonderful machines of ours... and
that is still a long way off.
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