MER press briefing, March 3, 2004
March 3, 2004Edit
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.
Benton Clark: Spectrometer science. You won't see pictures, instead see graphs, the two German instruments and mini-TES. Before we landed we had picked this area because TES on MGS had said it had interesting mineral content. First chart shows the APXS samples. Red is the original soil right off the lander. In the blue dots you see sulfur is much higher in the outcrop. Chlorine about the same. Bromine showing up on the right side. We had known that sulfur was high on Mars from Viking. Inferred at that time that it could be salts. When we analyzed rocks at Pathfinder and Gusev, the rocks didn't contain salts. At Meridiani that was different. At Meridiani, chlorine in green is small, sulfur is in yellow. Sulfur jumped up at McKittrick before we RATted. In third bar, the sulfur jumped up (after RAT) and at Guadalupe, we have the record on Mars, almost 5 times the amount. We interpret this sulfur to be sulfate so we expect magnesium sulfate, epsom salts, on Mars with less water it's called kesorite. Kesorite plus the chlorides add up to a salt concentration that may be 40% of the outcrop. This is astounding. No longer can be considered to be a volcanic construct. Only way you can form such large concentrations is to dissolve it in water and have that water evaporate. Further evidence is that the chlorine didn't go up. Also, bromine showed up high. Up at Guadalupe we have highest level of sulfur and down at McKittrick we have highest level of bromine and chlorine. We have an evaporative sequence. There should be additional salts in such a sequence. Next graph is the Mossbauer spectrum that has detected 4 types of minerals in McKittrick sample, including Jerosite, a large fraction of the iron, about a third. It forms in water at a fairly acid PH. Finally we have mini-TES that has looked inside RAT holes and found evidence of sulfate in the spectrum.
Joy Crisp: After a more close-up investigation we're going to want to broaden our view. How extensive was this liquid water. Our near long term plans include looking at younger material above the outcrop and on nearby plains. We'd also like to drive to Endurance crater. This graphic is a rover Pancam view of Endurance and a smaller crater between it and the rover. This MOC image shows large crater with bright rim around it. We're interested in finding out what that bright rim is made of. We've attributed it to being the older etched unit that underlies the hematite unit across the Meridiani plains. Is it the same as the outcrop bedrock? Endurance is 30 m deep so we would like to visit it. There's mottled plain to the south that we'd like to get to if possible. This MOC image is 3 miles across showing mottled terrain. We would like to find out if the bright material is the same or different from our outcrop rock. We will drive around and try to determine the water history for this area.
James Garvin: What an amazing time to be alive and doing science on Mars. What immediate scientific impact on our program. How can we use these results to target our program. Mars Reconnaissance Orbiter will do remote sensing from orbit and look for new landing sites. We have earth laboratories and we'd like to bring some of that stuff home to earth. We now have a possible target for a Mars sample return mission. These rovers are the first step to take us to see the new Mars.
Q. Does the data suggest how long the water was there or how deep?
Steve: I want to again differentiate between a standing body of water and water percolating up. We don't know if this bedrock was created in standing water. Best way to address the age problem is to see how extensive this stuff is, how thick this layer might be. Best way is to bring some of it back.
Q. How might you modify what you were going to do given more money and these findings?
James: over the last two years we have worked with our science community to craft a series of missions over the next decade. We've crafted those based on forecasting science. We have resilience in the science elements to follow up on these results from orbit and landers. blah, blah, Mars Lab, Astrobiology Lab, Sample return...
Ed. There are three things in the next decade. Sample return is clear. Both for scientific and in prep for human landings. Clear that we need in situ astrobiology missions. Third priority is to land some things that will prepare for human landings, test for toxicity, etc.
Q. any more on age?
Steve: getting at the duration of this specific formation event is going to be very hard. I'm intrigued by the possibility that something cool could turn up at our other landing site. If you want access to geologic information on these flat plains you need a hole. We got lucky at Meridiani. At Gusev, we landed 250 meters from a crater. These two sites are of different ages so if we find evidence of water at Gusev that would be interesting.
Q. If you found rocks like this on earth what are the changes you'll find life there.
John: I think the answer is simple, on earth, finding fossils in ancient rocks is very rare. Preservation is the problem. You target strategies to go looking for rocks where things would be preserved. This location could be a good candidate. You need to get around and look at a lot of rocks and different samples because there's a tremendous bias for preservation. It's a challenge.
Ben: In addition to physical evidence you can have chemical indications. (lost signal, sorry)
Q. what are key pieces of evidence for soaking rather than small amounts.
Steve: massive quantities of sulfates. with this quantity you have to have had a lot of water involved.
Q. Given geological context, if you find there was standing water, what does that imply about how large a body of water?
Steve: that's part of the reason I haven't fallen over that particular cliff yet. It's difficult at this site to point to a well defined basin. Mars can change its topography, eroded, tilted tectonically. This stuff may be fairly old. Fact that we don't see a well-defined basin I don't think argues compellingly against these rocks having been laid down in liquid water.
Q. Are there any geologic formations on earth that are similar.
John: whether this rock is the result of the accumulation of basaltic ash for which Hawaii is an example or if it precipitated from a salty sea. In another week or ten days we'll be able to get at that.
Q. Don't know how long ago the water was there? Millions of years, centuries?
Steve: when I said I didn't know, it's because I didn't know. In order to date this stuff you need laboratory quality equipment. In order to say how long it was there you need a complete stratigraphic section and we've only seen a small part.
Q. How long before you get up to Endurance crater, and secondly, what about the hematite?
Steve: it's gonna take us another week or 10 days in this crater. We want to go to Big Bend and look at ripples and cross-beds (if that's what they are). We don't yet know what those spherules are. There's a depression filled with these guys and we're going to go there and try to get a handle on what they're made of. Then we head out. As soon as we crawl out we'll find new and interesting things and want to take a good look around for a few sols then head across the countryside towards the crater. I think we'll make good time. Spirit is far out ahead but I think that's gonna change. We're looking at 50-100 meters per day at Meridiani. Several weeks before we get there. That is gonna be one heck of a view. With respect to the hematite, I've always looked at it as a chemical beacon visible from space saying that something interesting chemically happened here. There certainly is a lot of hematite here. I don't think we'll have a good answer until we crawl out of this crater. Mini-TES says highest concentration is above the crater.
Q. What might have happened here, lakes, rivers?
Steve: two possibilities. One, volcanic eruption and ash layers with lots of pore space then water percolates through that rock and deposits sulfates. Spherules grow, crystals grow and go away. Fundamentally alteration of the ash. Totally different scenario, you had a salty sea with currents, maybe waves, then as that stuff evaporates away, salt crystals settle out. Maybe that happens multiple times. Then you have water percolate through them and spherules and crystals grow. We may not find out.
Q. what do you mean habitable.
Steve: an environment suitable for life as we know on this planet. With respect to what this tells us about the atmosphere, not a whole lot. Could be groundwater, no surface water. If that's the case then it won't tell us a whole lot about climate. There's nothing like this going on Mars today.
Q. Can you say specifically what measurements in the next few sols to determine precipitated or percolation.
John: first look at last chance to examine some form of cross-bedding. Different geometries can tell us if there was a flow of fluids or an accumulation of sediment in a current. Minerology and geochemistry we hope to address formation process. The Dells and Slick Rock next. Most abundant set of MI pictures, some 2x10 images.
Q. What do we know about blueberries at this point.
John: We're going to wind up at the berry bowl, a hollow with lots of berries touching each other. There we can hopefully get their content.
Ben: keep in mind that we've only measured two spots on this outcrop and they're different.
Q. Cross bedding indicates strong current environment.
John: we're uncertain about the cross-bedding. We're hopeful and we're allocating time to test it. If there is cross bedding then we have to look at geometry in relation to grains that make them to understand the regime that created them.
Steve: at Bonneville we'll have access to a wider range of materials. Right now on the surface we're seeing basalt so there's volcanic activity. We need to get access to a wider range of materials.
Q. Is there any operational consideration that might constrain new outline of science.
Joy: no operational limitations. We foresee at least several more months. Something may break eventually and we have no way of predicting that. In terms of energy, thermal and mobility we don't see any reason why we can't keep going.
Q. Are you able to analyze rocks at opportunity to see if the rocks are basaltic?
Steve: By looking at the elemental and mineral composition we can say with a high-degree of probability at Gusev that the rocks are basalt and with certainty at Meridiani that it's not a pure basaltic rock.
Ben: one of the things we haven't done at Opportunity is measure a dark rock and there are some at the surface.
Q. If the water on Mars is briny, could it continue to exist?
Steve: it could, but you might have to go pretty deep to find it, 10s 100s of meters, maybe. As you go deeper it gets warmer.
Q. Are you announcing that water was stable on the surface of Mars in the past.
Steve: This could have taken place beneath the surface. This could be a groundwater thing.
Q. If there are organisms that like salt and there are microbes in Antarctic ice, can you look for life on Mars?
Ben: We do not analyze organic compounds on this mission. There will be future missions that may analyze organic compounds.
James: We can speculate but we don't know. Pessimistic view is that liquid water might be really deep.
Q. Some scientists suggest water could be near the surface in ice and might be released at an impact.
James: Phoenix mission targeted for ice-bearing soils will explore ice using its tools.
Ben: an impact crater could create conditions that would be warmer for thousands of years.
Q. Personal feelings about this important findings?
Steve: It's been interesting to watch all of the reactions. We all went in with our own prejudices, hopes, and desires. As we've accumulated the evidence the puzzle was coming together. It's been interesting to watch as we all came to the conclusion that water was involved. Some people made the leap right away, others took longer. It feels good. We worked for years to make this happen. On the other hand, we're just getting started. Maybe much better stuff out there. We're enjoying this but also chomping at the bit to get out there and look at more.
Ben: This group of scientists and engineers have been working unbelievably hard. Every day discoveries. Just the tip of the iceberg on this stage.