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Mars Up Close

  • By Lexi Krock and David Levin
  • Posted 12.30.08
  • NOVA

Ever since Spirit and Opportunity began relaying images from Mars in January 2004, scientists following them have employed an unusual lexicon, referring to martian "blueberries," "popcorn," and "deep-fried," "batter-coated" blobs. The intrepid Mars Exploration Rovers are discovering a landscape never seen before as well as offering new perspectives on a central question: Did liquid water ever flow on Mars? In this narrated tour, allow Steve Squyres, the mission's principal science investigator, to guide you through a handful of each rover's most stunning finds.

Launch Interactive Printable Version

NASA's Steve Squyres narrates a virtual tour of some of the Mars Exploration Rovers' most revealing discoveries.

Transcript

Mars Up Close

Posted December 30, 2008

SECTION 1: SPIRIT

STEVE SQUYRES: I'm Steve Squyres. I'm the Scientific Principle Investigator for the Mars Exploration Rover Mission. This is the landing site for the Spirit Rover. It's in a place called Gusev Crater. Gusev we picked 'cause it's a big hole in the ground with a dried up river bed flowing into it. It's a crater about 160 kilometers in diameter. The thing that's special about it is that flowing into the southern side of the crater, breaching its rim, there is an ancient channel, and it's a clear indicator, we think, that there must have once been a lake there long ago, and so we went to Gusev in hopes of finding sediments that had been laid down long ago in a lake. As it turned out what we got was a bit different from that, but that's what we went looking for.

This is the first good view that we got of the surface of Mars with Spirit after we landed. This picture was taken while we were still on the lander. We went to Gusev hoping to find ancient lake bed deposits. And we looked around and boy, it looked really smooth, it looked really flat, and we thought "yeah, maybe this is what a Martian dry lake bed looks like." As we looked more carefully though, we began to realize that maybe we hadn't found quite found what we'd come looking for. The rocks didn't seem to show sedimentary layering, they looked like they might be volcanic rocks. With time we came to realize that what we had hoped to find at Gusev crater was going to be a bit more elusive than we had originally realized. Mars had sort of faked us out.

When we first landed we took a look around, we saw a bunch of rocks. They looked suspiciously like volcanic rocks, despite the fact that we were expecting sedimentary rocks. And this was sort of a disappointment. But there was a hope among many people on the team that they might be something different. That they could be a limestone, that they could be sulfates, that they could be something exotic, something really different. So the one that we picked was the rock called Mazatzal.

We spent, oh gosh, it must have been something like 8 or 9 or 10 days at Mazatzal, it certainly was more than a week. And we drilled a hole in it with our RAT, we brushed the surface of it, we really cleaned it off and looked at it in detail. But when we ground through that with our Rock Abrasian Tool and looked underneath it was just a regular old basalt just like everything else.

Pot of Gold was a strange one. We landed on these flat plains, covered with lavas and when we landed we could see off in the distance a beautiful range of hills called the Columbia Hills. So after about 100 or so days of looking at the plains we decided we were gonna just to put the pedal down and go as fast as we could and try to get over to the hills before the rover died. We got to the base of the hills and everything changed. Suddenly we found ourselves among geologic materials completely different from everything that we had seen out on the plains, and the first rock that we got a good look at in the hills was Pot of Gold. I gotta be honest with you, we still don't really understand this rock. It's got this bizarre texture, it's got these little tentacle like things sticking out of it. A couple things about it have suggested to us that it did form as the result of action or interaction with liquid water. One is that when you look at the chemistry of this thing it is fairly rich in some elements like sulfur, chlorine, it's also got this mineral hematite in it which is sometimes formed as a result of the action of water as well. I wish that I understood it better than I do and I wish we'd find some more rocks like it, but so far it is strictly one of a kind.

So we got to the base of the Columbia Hills, we took a look around, and we realized that up the hill from us there appeared to be outcrops of real bedrock. And to a geologist, bedrock is very important, so we were really seeking bedrock. We had to fight to get to Clovis. Our vehicles were not designed for mountaineering. So when we got to the Columbia Hills we didn't even know if we could get up them. We got up to Clovis though and there, finally, we found ourselves on bedrock. It turned out to be totally different from anything that we saw out on the plains. So we put a hole in this thing, we looked at it with our microscope, then we stuck our spectrometers in, and it found a rock that had lots of sulfur in it, lots of chlorine in it, lots of bromine in it, lots of phosphorus, a number of different elements that are commonly formed in minerals that are easily transported by water. Now if you find all of these elements concentrated in a rock, that's a sign that water interacted with this rock. So we've got a number of different clues that the bedrock of the Columbia Hills has, in fact, interacted with water.

SECTION 2: OPPORTUNITY

STEVE SQUYRES: Meridiani. Meridiani Planum. That's where Opportunity landed. Very different from the Spirit landing site. The thing that drew us to Meridiani was not the topography, what drew us here was the composition of the surface. There's an infrared spectrometer on a spacecraft called Mars Global Surveyor that looked down from orbit and made a map of the chemistry of the surface of Mars, and in this location, and very few others, that infrared spectrometer discovered the presence of a mineral called hematite. It is a mineral that often, not always, but often forms as a result of the action of liquid water. Now it was a gamble. There are other ways to make hematite too that don't involve water, so we didn't know what we were going to find here, but we had a hint, visible from orbit, that this was a place where water might have once been.

Wow, this picture, boy this brings back some memories. This was a miracle. We landed at the Meridiani site with Opportunity, not knowing what we would see, expecting it to look different from anything else on Mars before. My biggest fear at Meridiani was that we would land on flat, sandy plains and there'd be nothing to see in every direction. No rocks, just sand, as far as the eye could see. In fact, what happened was we hit the ground, we bounced, we bounced, and bounced, with our airbags and we bounced and we rolled and we rolled and we rolled right into a little, 20 meter, impact crater. Right into it. I mean Tiger Woods could not have done this. We open our eyes, and the very first picture, the absolute first picture to come down from the spacecraft, showed layered bedrock 8 meters away from us. It was astonishing. And what we came to realize as we began to look at this bedrock in more detail was that the layering preserved a record of conditions that had existed at Meridiani Planum a long time ago and it was then our job to try to read that record and figure out what had actually happened here.

When we first looked down at the soil of Meridiani with our cameras we noticed that it was covered with what sort of looked like gravel all around the vehicle. And when we looked at them closely some of them, a lot of them, seemed to be really kind of spherical. So we rolled off the lander and down onto the soil and we whipped out our microscope and we took our very first picture of the soil in front of the lander and in that image there were two objects that were astonishingly round, I mean these things were spherical. And all of a sudden we realized "Hey, we're dealing with something really odd here." This is the one that kind of rocked us back on our heels and made us think, "We got a situation on our hands that's going to be very, very difficult to figure out here but it may be something really special." Though, boy I'll tell you, when we saw this one we didn't know what it was, we just did not know what we were dealing with yet.

After taking a look at the spherical objects on the soil in front of us and realizing the soil was just covered with these things, we decided to drive over and look at the outcrop. And this is a microscopic imager picture, it's only about 3 centimeters across, of the rock in front of us and it revealed to us our next astonishing discovery and that is that these little spherical objects are embedded in the rock, like blueberries in a muffin, that's when we started calling them blueberries. And the rock erodes away, it gets sandblasted over time, and then these hard blueberries erode out of the rock and fall out and tumble down the slope, where you find them on the soil. Now we knew where the blueberries were coming from, we didn't know what they were yet, but we knew at least where they were coming from.

This is a trench. We didn't bring a shovel with us. It would be nice to be able to drill deep holes, we didn't have that capability on this vehicle, but we did have the capability to dig trenches in the soil using the wheels, we sort of drive the rover back and forth, working one wheel down into the soil and digging a trench that's about 15 centimeters deep. What the trench showed us was a profile through the soil and we didn't know how these blueberries were distributed in the soil, there were certainly a lot on the top, we were wondering if it was densely packed with blueberries all the way down. In fact, it's not. The soil is mostly just basaltic sand, sand with the composition of basalt, and then it turns out it just has a layer of these blueberries sprinkled on top but very few of them in the soil below.

About 700 meters away from where we landed there was a much larger crater, one that we named Endurance Crater. It was about 150 meters in diameter, about 20 meters deep, and we had pictures from orbit that suggested that it had layered rocks exposed in the wall of the crater. Now if that was the case, that meant that we could use those layers to see what had come before the watery conditions that we had discovered over at Eagle Crater. We went down into Endurance Crater and what we found there was in fact that these layered rocks extend for many, many meters down. It seems to be blueberry-laden, sulfate salt-rich rocks all the way down, for like 10 meters down into this crater. And so what that says is that the period of water activity was significantly longer, it was more water, it was a longer duration, it was a habitable environment for much longer than just the rocks at Eagle revealed.

When we got deep down into Endurance Crater we found a lot of things changed. The chemistry changed, the texture of the rocks changed, and the blueberries changed. Up in the upper reaches of the crater the blueberries were nice clean perfectly round hematite spheres. You get down in the crater and you see this stuff that doesn't look like these perfect spheres anymore, it looks almost like popcorn or berries that have been sort of dipped in batter and deep fried. I mean I don't know what's going on here, they appear to have some kind of coating on the outside of them. When you look at these spherical objects deeper down in the crater you get a sense that many of them are conventional blueberries, if you can use such a phrase, similar to the ones that we see up the slope, but they've got a coating of salts on the outside of them and we don't entirely understand this yet, we're still trying to figure out what happened here.

This is a close-up of a rock that we called El Capitan. This is one of the first rocks that we looked at up close in Eagle Crater. You can see the fine laminations, the layering in the rock, you can see some embedded blueberries. And then there's something else in this one too and this was an intriguing thing about this rock. There are a number of places in this rock where it is cut through by little gashes in the rock. And they cut through the rock at all sorts of crazy angles, they're typically maybe a centimeter or so in their length, maybe a millimeter or two wide, and these are things that on Earth form when you have crystals of some mineral. Crystals grow in place if the rock is saturated with water, pushing aside or replacing the minerals that are there, and so now you have these tabular crystals all through the rock and then something changes, the water chemistry changes and the crystals dissolve away, or simply it dries up and over eons erosion erodes away the softer crystal leaving a hole in the rock around it, and so these weird tabular shaped holes in the rock were another hint that water was involved in the formation of these rocks.

This is the Berry Bowl, this was a fun one. We had these spectrometers that are very good at determining the chemical elements in the minerals in specific rock targets and we were really, really interested in finding what the blueberries were made of. The problem is, blueberries are little, they're only 4 or 5 millimeters across, and the field of view of our spectrometers is a lot bigger than that. So what we did was we looked for a place where there are a bunch of blueberries clustered together. And we looked and looked and we finally found this spot in the rock where there was a little bowl-shaped depression and a lot of blueberries had just rolled down into it and so there were a bunch of blueberries all clustered tightly together in this one spot, we called it the Berry Bowl. We stuck in one of our spectrometers and we found out the spectrum was incredibly rich in Hematite. Hematite is a mineral that commonly forms concretions which are found in sedimentary rocks on Earth and they grow from minerals that are precipitated out of liquid water that's coursing through the rocks. And this was one of our strongest pieces of evidence that we were seeing concretions, that we're seeing liquid water in the rocks.

Credits

Images

(all)
© NASA/JPL/Cornell

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