A.J.S. RaylApr 03, 2004

Mars Exploration Rovers Update: Spirit Finds Hints of Water in Mazatzal Opportunity Finds Hints of Hematite in Bounce Rock

The Mars Exploration Rovers continued to crank out scientific findings about Mars this week: Spirit sent home clues of past ground water at Gusev Crater; Opportunity set a one-day distance driving record and returned to the scene of her arrival, the rock she bounced off on upon landing at Meridiani Planum.

Spirit uncovered the clues of water while examining Mazatzal, a large, scalloped, light-toned rock. "This is not water that sloshed around on the surface like what appears to have happened at Meridiani," elaborated rover science team member Hap McSween, at the weekly press conference held Thursday at the Jet Propulsion Laboratory (JPL). "We're talking about small amounts of water, perhaps underground."

The findings are still being scrutinized, but water is what Spirit came to find. Now, in the days just before the end of her primary mission, it looks like she might have found it.

On the other side of the planet, at Meridiani Planum, Opportunity set a new driving record, cruising from the north side of the rim of Eagle Crater -- where she took the 'Lion King' panorama, to Bounce Rock -- so-named because it's the largest rock in the area that, as fate would have it, Opportunity hit on landing, when she was still protected by airbags. "What are the odds?" mused Jim Bell, lead scientist for the panorama cameras (PanCams) onboard both rovers. Compositional studies thus far indicate, he added, that Bounce Rock is of volcanic origin. "This is the first evidence we've seen for truly basaltic rock at the Opportunity landing site." Still, he cautioned that it's just "a supposition and hypothesis right now." It may have been quite a fortuitous meeting; the rover's studies are also hinting that there may be hematite hidden deeper inside.

At this point in the mission, the two rovers' 18 cameras have now taken more than 20,000 images cumulatively -- 16,000 of which are from Pan Cam, and returned a total of 2.3 gigabits of imaging data. And the data streams continue to flow well. Earlier this week, Spirit returned 114 megabits of data on one Odyssey pass, the largest returned to date from these orbital relays.

This weekend will be an important one for Spirit. In order to fulfill all of the MER mission objectives, one of the rovers must log 600 meters during the primary mission. Since Opportunity spent most of her time so far inside Eagle Crater, where she landed, and from which she only recently emerged, she has no chance of fulfilling that objective. It's up to Spirit. She hasn't got far to go.

As Spirit shuts down for the night Sunday, her primary mission will come to a close. The current plan calls for her to rove "seamlessly" into her extended mission Monday, her Sol 91. Opportunity still has three weeks to go to before her primary mission ends.

Spirit and Opportunity are starting, however, to show signs of aging, reported flight director Chris Lewicki. Specifically, "both spacecraft now -- most recently Spirit -- have seen the knee in the curve, as we call it, for dust accumulations on the solar panels," he said. "This has been talked about before where we've seen a linearly accumulation since landing, and from the Pathfinder - Sojourner day we know that at some point it kind of leveled off when we got a certain amount of accumulation on the arrays. We've seen that we believe now in both spacecraft. Our long-term energy story is what we were hoping."

All other parts of the spacecraft "aren't really showing any signs of wear at all," he added. "The batteries have been holding steady to the charge we've been giving them."

The rovers are changing seasons on Mars, going into fall, Lewicki reminded. "So the energy available during the day is a little bit less, and the temperatures are cooling down, and we're starting to more thermostatic heater cycling overnight on these survival heaters that keep the internals of the rover warm."

That reported, "Both spacecraft continue to perform very well," Lewicki summed up. "We look forward to a long lifetime on both spacecraft at both sites."

Spirit and Opportunity have transitioned to communicating primarily via their UHF transmitters, using Odyssey and Mars Global Surveyor as relays for nearly all the data, Lewicki reported. "In fact, Opportunity went 21 days without direct-to-Earth communications and we just broke that dry spell a couple of days ago. The only reason we did that wasn't out of need really, but just to make sure that the clock was still set right. We can only tell if the clock is right if we have direct-to-Earth communications, so we scheduled a special activity for that."

In coming days, the rovers will be given new leases of life when engineers upload new flight software. "The earliest we will start to upload is Tuesday, April 6, however that continues to move around," Lewicki said. "We have just a few remaining issues with the test of the new flight software load that are being closed out and we want to make sure that we're thorough while we still have out complete team and can resolve any issues we're having. We're looking at loading that over 4 days on both spacecraft and potentially booting into that new flight software on April 10."

On these 'stand down' days, the science will be reduced, but they will not be "science-devoid days," Lewicki noted. "There will be a lot of spectrometer integrations, because those can kind of happen in the background and we hope to make up a lot of our downlink deficit in terms of data that's onboard in flash since we won't be generating a lot during the day."

"The science that we'll be doing on those stand-down days involves the Mössbauer spectrometer and the alpha particle x-ray spectrometer (APXS) - both of which can benefit tremendously from long integrations," McSween pointed out. "So we hope to clock maybe two days worth of integrations on both instruments to significant improve their signal-to-noise ratio. Then we may be able to go back and look at some of the old data. For example, with APXS extract some trace element data that we can't extract now. It has a tremendous opportunity give us a good pay-off in science."

"One other aspect is that Mars is helping us in the power situation, because the opacity of dust in the atmosphere has been steadily decreasing in time - I think it'd down by almost a factor of two since the start of the mission," Bell added. That means the rovers are getting more sunlight that's less filtered by the dust. And that, he said, should "compensate a little bit for some of these power issues."

Spirit From Gusev Crater
Sols 83 -89

At Gusev Crater, Spirit has devoted most of her week this week examining the rock Mazatzal. Last Sunday, the rover used her rock abrasion tool (RAT) to grind the deepest hole to date in a rock on Mars - 0.31 inches [8 millimeters] into this strange, light-toned, scalloped rock. Inspired by their success, the team instructed the robot geologist to tackle the target Brooklyn right next to her New York 'bulls-eye.'

On Monday - Sol 84, Spirit set up her mini-TES and PanCam and recorded observations of Bonneville Crater, and then completed a successful Mössbauer integration on the hole she had RATed Monday in Mazatzal, to find out what iron-bearing minerals are in the rock.

Additional investigations with the instruments on her arm had to be postponed however, after a switch on the Mössbauer spectrometer stuck. It turned out to be a 'false error,' mission control determined, and even though the switch was actually properly 'flipped,' the rover waited for commands from the ground, just as she was programmed to do.

Spirit RATed both the New York and Brooklyn targets on Mazatzal on Tuesday, then devoted the rest of her morning to analysis deploy her microscopic imager (MI) to take a more detailed look inside the freshly RATed holes.

Later, the rover took PanCam images of her RAT work then turned the camera on Bonneville Crater to take few more pictures that may be used in a super-resolution image of the heatshield remnants on the far wall. Spirit then used her PanCam to take some more pictures of the drive direction, as well as images for the 'catch-a-dust-devil' in action project. Before her day was over, the robot field geologist used her mini-TES to take the last observations of sections on Bonneville Crater and acquire some more ground and sky stares. After taking just a few final MI pictures, Spirit placed her Mössbauer spectrometer in one of the holes and began an overnight integration.

The rover was doing well, moving through every command and task like clockwork on Tuesday. But down at mission control at JPL, the engineers were not having a good day. Although Spirit had done everything just as she was told -she forgot to acknowledge to her ground team that she was in fact carrying out her commands. The team had uplinked her daily agenda as usual, and waited for the acknowledging 'beep' that confirms Spirit has received the uplink and has activated the sequence. The 'beep' never arrived. The redundant second 'beep ' 10 minutes later also failed to arrive. That was when the engineers started getting a little concerned. They hadn't been able to find any errors in going through their trouble-shooting procedures.

That afternoon, however, they received 75 megabits of data from Spirit's communication with the Mars Odyssey orbiter, right on schedule. That told them Spirit had received her daily orders and had completed them as per the program. Everyone in mission control breathed a sigh of relief, then turned their attentions to investigating why Spirit hadn't acknowledged her ground team.

Wednesday was another full day for Spirit. The rover woke up and turned the heat on her panoramic mast assembly to complete ground and sky stares with the mini-TES, and then completed the APXS integration on the hole. Following her morning nap, the robot geologist prepared for her final experiment on the Missouri target of Mazatzal -- using her RAT to perform a six-position, brush mosaic. Essentially, she scrubbed the surface in a pattern of five circles arranged in a ring, with a sixth circle in the center. The impression looked like a daisy.

"We used an expensive and very high-tech instrument to do something very primitive to a rock, something we do on Earth - it's called a petroglyph," said science team collaborator Steve Ruff, of Arizona State University. "We scraped away the surface of a rock on Mars and what we've done is made a semi-permanent feature of art that we call the RAT daisy. We hope that will be preserved for some time in the future, a nice example of something primitive and high tech at same time."

Besides creating a pretty cool rock-art daisy on Mars, JPL and Honeybee Robotics engineers had succeeded in producing a brushed patch big enough to fill the field of view of Spirit's mini-TES, which was the purpose of the exercise, Ruff noted.

After taking pictures of her flowery impression, Spirit stowed her arm and left her flower in the rock, rolling backward 2.95 feet [.9 meters] to position herself to be able to acquire mini-TES images of the newly brushed mosaic, and the previously ground hole. She also took more sky and ground stares, and more PanCam pictures of the upcoming drive direction, ending her day with mini-TES stares at the Columbia Hills and an afternoon pass by Odyssey.

Back at JPL, science team members were in their offices and cubbyholes sifting through and analyzing the data Spirit had gathered from Mazatzal and was sending home. Named after the mountains in Arizona, Mazatzal lies partially buried near the rim of Bonneville Crater, inside the much larger landing zone of Gusev Crater. This large, unusual light-toned rock that appeared to be scalloped by the winds had caught their eyes the first time they saw it. Their intuitions and curiosities looked to be paying off.

"Evidence of water at Gusev is hard to come by," McSween contended at the press conference. But, just before her primary mission is about to end, Spirit has found, at the very least, evidence for trickles of it flowing underground.

"There were hints before when we looked at some of the other rocks in the area, but for the past week we have been parked at a rock whose name is Mazatzal -- and Mazatzal gives us the most enticing information yet about water," added McSween, who is from the University of Tennessee, Knoxville. "The evidence is in form of multiple coatings on this rock, as well as some fractures that are filled with alteration materials and perhaps some little patches in the rock that represent alteration materials as well. Mazatzal is basalt like the other rocks in the region, but it has clearly been altered by interaction with fluids."

Images of the areas of Mazatzal that Spirit brushed and RATed revealed that under the lighter, tan-colored topcoat, are at least two more layers -- a dark layer, then a lighter gray interior appears below, both of which are marked by a bright stripe. Science team member Jeff Johnson, of the U.S. Geological Survey's Astrogeology Team, suggested that the stripe "seems to be a fracture that water has flowed through, potentially with minerals precipitating from that fluid and lining the walls of the crack."

The light outer coat, dark inner coat and bright veins could have resulted from three different periods of the rock being buried, altered by fluids and unburied, McSween theorized. "It could be we have three different periods of alterations and we need to bury the rock each time and expose it to subsurface fluids and then exhume it and each time you do it, the fluid composition is different, the conditions are different. And so the nature of the alteration is different each time.

"It's also possible though that the coatings on the surface of this rock don't necessarily require burial," McSween continued. "I think the precipitation in the fractures probably does, but the coatings could conceivably be due to some kind of surface process. There are rocks formed in desert regions on the Earth, called desert varnish that form coatings by processes that are not well understood and at least some of these coatings look superficially like desert varnish. But even there we might need some high humidity, something has to act to cement this material onto the surface. There are various scenarios right now and we don't have enough information to try and pick and choose between the various alternatives."

While McSween, Johnson, and Rieder stressed that the interpretations are preliminary, the discovery of water is a significant finding, obviously, if it bears out. "The team is, as always, trying to find time to digest these observations while also preparing for the next day's operations," Johnson reminded. "What we're seeing though is truly unprecedented."

Other data that Spirit has collected are adding more clues to the mystery of the water story at Gusev. Rudi Rieder, of the Max Planck Institute in Germany, lead scientist for the alpha particle x-ray spectrometer (APXS) on board both rovers, has been reviewing the chemical measurements Spirit has recorded with the instrument, from areas close to the surface of untreated, brushed, once-drilled, and twice-drilled patches.

"I personally feel very much like on a tour through a flight of rooms in a European royal château, because we keep on opening one door, entering a kind of red chamber, and there's another door that leads to a blue chamber, and a third door that leads to a green chamber -and we don't know how many chambers we still have to visit," Rieder analogized.

In an analysis of soil patches, Rieder's team correlated two elements considered characteristic for soil and dust on Mars -- sulfur and chlorine. "Much to our surprise when we started brushing it, the sulfur content didn't change, but the chlorine went up, which may [mean] underneath the first upmost layer we are seeing a second layer which is still not rock, still contamination, still sort of soil. And only when we started RATing did both sulfur and chlorine come down." What that means, he said, is that "we still have not removed all of the contamination yet, but we are going the right way."

Another plot, showing the APXS' measurement of the concentration of chlorine versus bromine in the rock, may have, Rieder said, some bearing on what may be hidden in the cracks. The APXS data show that the ratio of bromine to chlorine inside the rock is unusually high, something that is a possible clue to alteration by water.

"These two elements are chemically very similar; they're both halogens," Rieder explained. "And it's very difficult once you have made a mixture of the two to separate them from one another again. But we have already noticed on Meridiani, that on Mars there is something that separates them -- and it separates them stronger than we know from the Dead Sea, where we have similar effects by evaporating Dead Sea water."

The latest datapoint from Spirit's APXS work taken from the Brooklyn site on Mazatzal, Rieder added, "indicates that again we have some very strange behavior between chlorine and bromine. But what is even more important, the concentration of bromine is probably due to only what is contained in this tiny crack, and the cracks may be much richer, because they only cover a tiny fraction of a few percent of the total field of view that we see -- so miracles, miracles, miracles -- we've got a lot of work to do."

Preliminary analysis from the mini-TES measurements of the daisy Spirit ground on Mazatzal reveal that the tan outer surface appears to have a strikingly different mineral composition than the dark gray coating exposed by the brushing, Ruff announced. "This is something we're very excited by, because in the previous RAT operations that mini-TES has viewed, we essentially saw no difference spectrally," he explained "That had been a frustration for us, but now this rock, Mazatzal, has provided our first before and after that's dramatically different."

Contained in the before and after spectra, are "the details of the mineralogy related to probably the two different coatings we're seeing now with a multitude of different datasets," Ruff continued. " We are probably seeing mineralogy in that light-toned surface, and we're probably seeing mineralogy attributable to that darker rind. We have yet to get into what those minerals may be, but what we can probably tease out of this is whether these minerals are related to water processing or not. So we're anxious to go to work on them."

While more time is needed to complete the analysis, this is "an exciting result," Ruff concluded. "We have now spectra of two different brushed surfaces. Each one of those spectra is different, each containing its own mineralogical details, and that detail may tell us something about water interaction with these rocks on Mars."

On Thursday - Sol 87, after working on some atmospheric science in the morning, Spirit took one last look at Mazatzal with her PanCam and NavCam, then she was off down the side of Bonneville Crater and south toward the Columbia Hills. She put another 119.8 feet [36.5 meters] on her odometer, in what was a 'combination' drive -- part blind and part autonomous navigation (AutoNav) roving.

The blind segments of a rover drive are used when planners can see all possible hazards and command the rover to just 'go.' The AutoNav portion allows the rover to make decisions based on the terrain presented. But this time the 'combo' drive didn't help Spirit log the distance the team hoped she would. Truth told, the rover team had hope that Spirit would really scream Thursday.

Everything was going swell until the second to the last autonomous navigation sequence did not complete in the allotted time, causing a drive 'goal' error - and because of that the rover was not able to execute the complete commanded drive. As impressive as her 119.8 feet [36.5 meters] distance is, the team was looking for something more like 213.3 feet [65-meters]. Stuff happens. It didn't bother the rover. Spirit got right back to work snapping some more NavCam and PanCam pictures in her drive direction, and conducting some atmospheric and soil science with the PanCam and mini-TES from her location.

The robot field geologist at Gusev began her Friday - her Sol 88, by conducting some remote sensing work, including PanCam photometry and a mini-TES stare at a rock called Carlsbad. Then she put it into gear and drove for 114.8 feet [35 meters] down the rocky, ejecta-covered side of Bonneville Crater.

It was another 'combination' drive. Rover drivers took control for part of the way, and part of the way Spirit drove. During the time the drivers were directing the drive -- about 49. 2 feet [15 meters] -- the rover didn't have to use her hazard avoidance software, she was able to rove a little more swiftly. The remaining 65.6 feet [20 meters] were navigated by Spirit autonomously. As a result, the rover had to make some back and forth adjustments as she avoided what she perceived to be a depression hazard in her path.

While rover controllers looking at hazard avoidance camera images today to confirm the details of Spirit's behavior, they'll be instructing her to drive so more. Cruising is what it's about for Spirit this weekend, chasing one last mission objective of putting 600 meters on the odometer.

As Spirit roves, the science team will continue to check out all the data she's sending from her study of Mazatzal. The study is "very much a work in progress," said McSween, noting that the research was still coming down from the orbiters.

Spirit is now into what is destined to be a record-breaking journey, the trek to the Columbia Hills, 1.3 mile [ 2.3 kilometers] away. "The idea here is that, if there is a more glorious water story for Gusev, as was implied by the original hypothesis that Gusev was once a lake, then that record is going to be kept in the stratigraphy of the area," McSween reminded. "We haven't found that stratigraphy in Bonneville Crater, and so we're hoping that we may find it in these more distant hills."

"It's not just a guess -- there are good images from Mars Orbital Camera onboard the Mars Global Surveyor that do show evidence for layering or other kinds of possibly sedimentary structures, so we do have some evidence for making the drive and making the attempt to find this water story in that area," added Bell.

When Spirit shuts down Sunday night, her primary mission will be over. Although this little rover didn't return the big splash of a water story that her twin sister Opportunity did, you'd be hard-pressed to find a science team member who hasn't felt that Gusev has been enlightening.

"The major discoveries for the first 87 sols of Spirit have been that the surface really did not look like we predicted before we got here," McSween summed up. "There are a lot of basaltic rocks we found that are like the rocks that we have seen elsewhere on Mars in terms of compositions. So they're very interesting from that perspective. Until Mazatzal, though, they really haven't told us about water at the site. The goal of extended mission, I think, will be to flush out this story a little better and seek stratigraphic evidence that might tell us about a grander role for water at sometime in the geologic past at Gusev."

"If you extend Rudi's analogy of opening a house -- every time we go someplace new we see something we haven't seen before," added Johnson. "The goal of mission is exploration and discovery. Every day we drive. I think we'll see something new -- if we can get to hills that's going to be something we've never seen before and who knows what we'll see on the way?"

"One of the recurring comments about the Gusev site is that it's unlike Meridiani, which is fairly unusual for the whole of Mars," added Ruff. "Gusev probably represents Mars more globally, so processes we see occurring at Gusev are probably ones that are occurring elsewhere on the planet. We can extrapolate what we know and what we're seeing from Gusev to other places on Mars more so than [we can with] what we see at Meridiani, which is really a kind of unique place. We're excited to have this ground truth that we can expand and extend across the rest of Mars."

Come Monday morning, Spirit will be woken, just like she has been every morning since she got there, and will rove seamlessly into her extended mission.

Opportunity From Meridiani Planum
Sols 62 - 68

Although everyone is anxiously awaiting the 'Lion King' panorama that Opportunity finished taking last weekend, the data bits are still coming down from the orbiters, Bell announced at the press conference. Even from the first bits, it promises to be some picture.

"It is the largest panorama we've obtained to date on either mission, consisting of 558 images in eight parts, six filters, 75 megabits of data, " said Bell, adding that it took two days to acquire. "We're still trickling it down to the ground, and it's going to take many more days to calibrate the maps," he added, as he presented one piece of it, a shot taken of the area right in front of the rover.

Although it did somewhat limit the size of other imaging data that the rover could store and send, the team agreed that "it was an important product," said Bell. "It actually impacted our data collection strategy over the days following acquisition of the panorama," he said. "We filled up the flash to levels close to the comfort level of mission management and basically had to go on pixel diet in days following to make sure we could downlink more than we acquired everyday -- otherwise you can't pull the panorama out of flash. It did have somewhat of an impact in limiting the size of imaging data . . . but we've been trying to carefully manage it and get the data down in a reasonable amount of time."

The Lion King panorama is part of a set of panoramas being taken on both rovers, Bell said, that will "tie the different parts of the landing sites together and relate it to orbital data."

After Opportunity finished taking that panorama last Saturday, she set a one-day driving record by logging 160 feet [48.9 meters] on the trek to Bounce Rock. "There was one big rock out on those plains and we managed to hit it," Bell said, still amazed. That drive put her almost to her destination, the scene of her arrival, where she would examine the rock she hit on landing January 24.

The robot field geologist seemed ready to wake up Monday morning and get to work, but then she encounter an 'error' and everything came to a screeching halt. Once the team on the ground received the 'error' message in response to the sequences it had uplinked, their day was suddenly devoted to figuring out what that meant. Turns out, it wasn't that big of a deal, although Opportunity was temporarily out of commission.

"What happened is we uploaded the sequence files and it got written to our non-volatile ePalm memory -- this is different than the flash memory which Spirit had an anomaly with early in the mission," explained Lewicki. "The reaction was when you're writing to the memory and you read it back and it doesn't quite compare, the spacecraft, as an effort to be safe and redundant, saw there was an error in writing that sequence to the memory, so it took that sequence area offline. We do have two redundant areas on the spacecraft for storing these sequences, so that didn't impact operations at all."

The team did take Tuesday as an 'engineering only' day to characterize that problem, recover that memory section, and place it back online. They found a corrupted file in the area where the rover commands are addressed and stored, effectively fenced it off and contained it, preventing it from harming any future command sequences. "We understand the problem completely now, and things are in place so that particular problem won't occur again." In the end, Lewicki said, it may just be sign of "maybe just a little bit of age starting to show on Opportunity."

The second Mars Exploration Rover spent the rest of the week investigating Bounce Rock. "The rock is unlike any seen on Mars before," said Bell, who is from Cornell University. "At first, we called it Bounce Mark Rock, because it was right next to one of those bounce marks that we could see, where the airbag and lander assembly inside the airbags bounced across the plains before coming to rest inside the crater. It was enigmatic, dark, funny looking, and a little bit fuzzy [when we first saw it], because it was off 40 meters or so from the rover. We weren't even sure what it was. In fact, there was some significant debate as to whether it really was a rock or whether it might be some spacecraft part or airbag piece and something related to the fact that we bounced right through there. But we knew there was this enigmatic thing out there and it had some different color properties and maybe different morphologic properties than what we had spent more than 50 sols investigating inside crater, so it was an obvious target to think about hitting once we got out."

On Wednesday - Sol 65, Opportunity's first real day back to work after her 'error' glitch, the rover was woken up to Arrowsmith's "Back in the Saddle. The rover must have approved for she got rocked right back to work conducting some studies of the atmosphere with her mini-TES. After that, she imaged the atmosphere with PanCam and then turned the camera on Bounce Rock. Later, she moved in really close with her microscopic imager, then put her Mössbauer spectrometer on a target chosen by the science team. Still later, the rover took some more pictures with her navigation camera (NavCam) and PanCam, and completed more mini-TES science.

On Thursday, Opportunity was ready to rock - err, RAT Bounce. No April fooling. But first she used her APXS to measure the target called Glanz2, located on the rock, and took some mini-TES measurements of the ground and sky. Then, she pulled out her RAT and homed in on Case, the targeted area for the grind. For two hours, she worked away, producing a quarter-inch [6.4 millimeter] hole that will allow he to get her spectrometers in there to analyze the composition. She put the Mössbauer spectrometer on first, for an overnight integration. Later, after her afternoon nap, Opportunity also took some more atmospheric science studies with her PanCam and mini-TES.

Opportunity's work at Bounce Rock continued Friday as she switched instruments and examined the rock with her MI and APXS, and spent the afternoon closely examining a handful of targets on the rock.

Along with her examination of Bounce Rock, Opportunity and the MER engineers managed to sneak in some engineering studies, characterizing the driving on Meridiani Planum and doing some visual odometry experiments where the rover used her camera system to track differences between pictures, step-to-step, which will help them pick more appropriate parameters for use during the "long-haul" driving in the future.

"We've experienced slips inside Eagles Crater, anywhere between 2% to 100% when we tried to exit the crater," Lewicki pointed out. "We're also see some slip on the flat plains, based on the visual odometry, but what's interesting is it's slip in the forward direction. This might be indicating that the parameters that we have set for how big our wheels are -- which is how we determine our odometry -- might be just a little too large base don what we're doing, so we might make some adjustments there.

In an aside, Lewicki also announced that Opportunity had picked up a souvenir from Eagle Carter, "Usually when you go to exciting place, you take pictures and if you're a scientist maybe collect a few spectra. The engineering team was feeling a little left out and we were thinking - 'What do we need?' 'We need a needed souvenir. As fate would have it, sometime around when we left the crater we picked up a souvenir." It's a tiny little rock, which Opportunity is keeping tucked in her right front wheel well as, Lewicki said, "a reminder of Eagle Crater and the good times when we near the lander, which we'll never see again."

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