March 3, 2004
Dr. Ed Weiler: three and a half years ago, several of us on this stage to tell you about our plans to send two rovers to Mars to investigate water on Mars. We'd just suffered two failures. You're about to hear that Opportunity has landed in an area of Mars where liquid water drenched the surface and was around for a habitable time. Today's results are a giant leap.
Steve Squyres: Ever since Opportunity touched down on Jan 24 we saw this marvelous outcrop right in front of us we've been trying to puzzle out what it has to tell us. For the last two weeks we've been attacking it with everything we have. Every piece of our payload have been used. Over the last couple of weeks the puzzle pieces were falling into place. We've concluded that these rocks were soaked in liquid water. Were they laid down in liquid water? we don't have an answer yet. Were they acted upon and altered by liquid water. We believe yes. First, the little spherules like blueberries in a muffin are embedded int his rock and weathering out of it. Three ideas, lapilli, little volcanic hailstones, one possibility. Two, droplets of volcanic glass or impact. We've looked at these things very carefully. Probably concretions. If so, it's pointing towards water. Second piece of evidence is that when we looked at it closeup, it was shot through with tabular holes. Familiar forms. When crystals grow within rocks, precipitated from water. If they're tabular, as they grow you can get tabular crystals and water chem changes and they go away or they weather away. Next piece of evidence comes from APXS. We found it looked like a lot of sulfur. That was the outside of the rock. We brought with us a grinding too, the RAT and we ground away 2-4 mm and found even more sulfur. Too much to explain by other than that this rock is full of sulfate salts. That's a telltale sign of liquid water. Mini-TES also found evidence of sulfate salts. Most compelling of all, the Mossbauer spectrometer in the RATted space showed compelling evidence of Jerosite, an iron sulfate hydrate. Fairly rare, found on earth and had been predicted that it might be found on Mars some day. This is a mineral that you got to have water around to make. We believe that this place on Mars had a groundwater environment that would have been suitable for life. Habitable place at one point in time. This is a place where minerals precipitated out from liquid water. One of the best kinds of rocks that preserve evidence for life are rocks where minerals precipitate and trap and preserve evidence of past life. These are very, very interesting rocks. Just as a teaser, we have tentative evidence that not only were they modified by liquid water, they may have been laid down by water. Once we have finished up on El Capitan, we're driving to Big Bend and we'll take some very detailed pictures to try to determine whether these rocks were laid down in liquid water.
John Grotzinger: Geological field trip to el capitan location. All the observations fit together in a very specific way to narrow down the case for a specific story of what we have. This movie will show opportunity ledge, about 20 meters wide, 20-35 cm high. Color change, fault, ubiquitous layering. El Capitan, has well preserved textures and layering. We see lamination, the voids steve was taking about and the blueberries. Another still shows this fine layering and one of these spherules. Laminations don't deflect around it. These spherules are concretions that result in the displacement of materials rather than pushing the layers down like they would if they were lapilli. Also, randomly distributed, not in layers. These tabular voids show greatest width in the middle and tapering at the ends. Reminds us of gypsum. Requires water percolating through the pore network. Their absence may be evidence of fluid erosion too. In the next slide, we have where we're going in the future, 7 days of experiments to evaluate rock Last Chance. See layers that are cross-bedded, (only a hint) it requires sediment particles be moved in a flowing current, could be air, could be water, could be volcanic gasses. Experiments designed to help test that out.