Destination Mars

by Rod Pyle

  Opportunity then moved toward its most attractive immediate target: the freshly named Opportunity Ledge. In an area dubbed El Capitan, an outcrop that displayed what were apparently different kinds of layering and weathering from top to bottom. This is the kind of thing that sets a planetary scientist's blood aboil, a four-inch molehill named after a mountain in Texas. After much visual examination, the RAT set to work grinding away. Once this was complete, besides showing the expected profile of a layered rock, two round shapes were visible. Known as “spherules” in the trade, they excited the researchers to even greater heights. About the size of BBs, averaging about one-sixteenth of an inch, these were later named “blueberries.” They can be formed by different geological processes, and, as is so often the case in geology, the context in which they are found can have a lot to do with how they are interpreted. But finding them here, inside a rock on Mars, was downright dreamy. More were found nearby, both inside the outcrop and on the ground.

  But there was more. Empty areas, called vugs, were laced throughout the ground area. These hollows were consistent with comparable terrestrial rocks where something had been dissolved—by water—after the rock formed. To add to the mounting evidence, the spherules were found to be composed of waterspawned hematite. Further work with the spectrometer revealed another mineral, jarosite, which is also formed in water—more evidence of a watery past. This is the kind of evidence planetary geologists love—three distinct sources of aquatic evidence had emerged in one location, and things were looking good.

  On March 2, JPL announced that water had at one time flowed through the rocks, changing their texture and chemistry. While these words may not sound profound to a layman's ears, from ever-cautious planetary scientists, they are almost ironclad. There had been water, and probably a lot of it, in Meridiani Planum.

  It was the first victory dance, albeit a low-key one. Time to move on.

  Spirit meanwhile reached a crater called Bonneville. It peered cautiously over the edge, looking for points of interest. Across the crater, about five hundred feet away, the rover spied its own heat shield, which came to rest there after being discarded during the craft's descent. While the crater looked inviting, and while the end of Spirit's primary mission was drawing near, it was elected not to risk descending into the crater, and Spirit, prompted by its earthly controllers, moved on. Far off, across the floor of Gusev, the Columbia Hills beckoned. Soon the rover was over one thousand feet away from its lander; a pittance by human exploration standards but a vast distance for a Martian rover.

  Back at Meridiani, Opportunity had left the rocky outcrop that had consumed so much of its short life. Greater adventures lay ahead, as it spent some time evaluating the skies above—including observation of a somewhat rare transit of the Martian moon Deimos across the face of the small and distant sun. At only nine miles across, Deimos would not block the sun; it was merely a speck on the face of our star. The rover next began a long look at a rock euphemistically named Last Chance, which it had come upon as it neared the end of its primary mission. Then there was a bit of a showstopper.

  In a wide-angle picture of the area, a bizarre-looking object appeared. It was the wrong color to be here; it was also the wrong shape. It looked like…the head of a rabbit. Now, planetary researchers are not the type of folk given to flights of fancy, and most anything other than a beer can or an abandoned Chevy Corvette® found on Mars is going to find a bunch of men and women huddled around monitors, seeking a logical explanation for what they are seeing. But when something appears that triggers the human impulse to make a familiar shape out of the unfamiliar, especially in a place where it is so unexpected, let's just say that it is a reason to pause and reflect.

  And then, just as they were taking a better look…the two-inch yellow oddity vanished.

  The first assumption was that it must be man-made, something that came from Opportunity as it was landing. Lots of events occur during a landing cycle, and some are somewhat violent. Little bits can fall off a lander as it plummets to Mars, especially when it lands the way the MER spacecraft did, bouncing to a final stop. But the color didn't quite match anything they could think of on the lander, though it had a general resemblance to the material from which the landing bags were made.

  A painstaking examination of other images taken earlier revealed the bunny closer to the lander. Aha. Then one bright soul performed a spectrographic analysis of the object and compared it to the stuff from which the airbags were made—and it was a match. Later the object was spotted hiding underneath one of the petals of the lander. The final conclusion reached was that it was a piece of torn airbag material after all, that had been blown around by light local breezes. Mystery solved, and not too soon, for on a mission of this magnitude, one can't have researchers spending too much time on any one problem unless it is promising of a relevant discovery…and while the bunny did appear to be shy in its choice of a final hiding place, it was pretty clear that it was not a living thing nor an ancient Martian artifact. In the end, one of the more arcane mysteries since the Face on Mars had, again, been solved via patient thought and analysis. But it had been fun.

  More rocks lay nearby, begging for analysis. Opportunity continued to look at Last Chance, snapping 114 microscopic images of the rock. As an example of what it takes to conduct such a seemingly simple task, controllers had to send up about four hundred commands and reposition the robotic arm two hundred times. But what they found was worth the trouble.

  The rock was a sedimentary feature and showed what geologists call “cross-lamination,” a sure indicator of water-deposited sediments. Further, these were laid down by flowing water, not merely a pool. Evidence was mounting that Opportunity was not merely in an area “drenched in water,” as one press release quoted, but better still, had come to rest in a former coastal area of a large sea.

  This area was a bonanza for the geologists. Opportunity went on to examine more rocks and features before leaving Eagle Crater. One such area was called Berry Bowl, because it was host to a number of the “blueberries” seen near and inside of El Capitan. The hematite spherules were more far common than suspected. Although the individual “blueberries” were too small for the spectrometer to be entirely accurate, here there were a sufficient number of them that the instrument could get a reasonably good reading; and they checked out as hematite.

  Opportunity soldiered on, wheels slipping a bit in the loose soil as it departed Eagle Crater. It was off to explore the promising Endurance Crater. At about 430 feet across, Endurance was far larger than Eagle, and other than a lone rock in the area, the only feature of interest nearby. It was 2,300 feet away, much farther than the rover's travels to date. The Sunday drive would be leisurely and slow, but not without more potential for discovery.

  Across the planet, Spirit continued its mission, steady and sure. If rovers had emotions, surely this machine—only the second mission to land on Mars and first of its generation—would resent its higher-profile sibling. By no fault of its own, Spirit had landed in an old lava flow inside a crater, with little to offer beyond some smaller craters that might provide some insight. Compared to Opportunity, which had struck pay dirt, it was a distant second at this point in time. A bit like hitting a vein of pyrite when your neighbor hits gold. Not the worst thing, but a pale second place.

  Fortunately, robots have no hearts to break. Spirit looked toward the Columbia Hills, just over a mile distant, and rolled onward.

  Steve Squyres came to space exploration with a pedigree: first there was Cornell, one of America's finest universities, where he earned a doctorate while studying under Carl Sagan. Then there was that postdoc at NASA Ames in California, not given lightly. Then Cornell asked him to return to his alma mater as a professor, something not often done in the top tiers of academia. Oh, and let's not forget the H. C. Urey Prize from the American Astronomical Society in 1987, or his 2007 Benjamin Franklin Medal in Earth and environmental science.

  But to talk to him, it
is clear that all this pales next to his time spent on Mars, at least through the telerobotic senses of his Mars Exploration Rovers. His interest in exploration of faraway places started early: “I grew up in a household where people were interested in science; I was interested in science at a very young age. I was also very interested at a young age in exploration. I loved climbing mountains when I was a kid; we used to take faraway vacations like Colorado. I was also as a child fascinated by the history of exploration, so I used to read a lot of exploration books about the Arctic and that sort of thing. Science and exploration were all things I was interested in.”1

  Studying geology seemed to be a gateway to far-off places on Earth, and for many geologists, it is. But there was a problem: there were not very many places on the maps of Earth that were still terra incognita.

  “What I discovered after two or three years of being a geology major was that the scientists who have been doing geology on Earth for centuries have [already] done a pretty good job at figuring things out. So for someone who thinks of himself from an explorer's perspective, it felt like filling in the details, and I was interested in more of a blank canvas.”

  That canvas would be his, and filled with a ruddy red…

  “My third year at Cornell I took a course on results of the Viking mission to Mars, which was happening at the time, 1976 and 1977; it was a graduate-level course, so because of that we were expected to do a piece of original research for our term paper. I got a key to the Mars room, which stored pictures from the Viking expedition and orbiters. I remember going into that room and looking at the pictures for four hours, trying to find out what I was going to write about, but I walked out thinking about what I was going to do with myself. And then it was obvious, this is what I was looking for.

  “I switched gears, went right into planetary science, applied to a bunch of different grad schools. This was at the time of the Voyager mission, and while I was deciding where I was going to go to grad school, Carl Sagan approached me and told me he'd be interested in having a grad student on the Voyager mission, so I worked on Voyager while I was in graduate school. It was a fabulous experience and I've been doing planetary exploration ever since.”

  Since Voyager, and in addition to professorial duties, Squyres worked on both the Magellan Venus project and the Near Earth Asteroid Rendezvous mission with JPL. But Mars was still out there, beckoning. He got interested in the idea of Martian rovers as a follow-on to Viking, and soon found himself the principal investigator for the Mars Exploration Rovers.

  “The primary goal of MER was to go to two places on the Martian surface, trying to learn what conditions were like there in the past, and then find out when they might have been habitable. Mars is a cold, dry, desolate place to stay, but…in the past, conditions may have been different. So we tried to choose two places that appeared from orbit, first and foremost, [as a good] place to land on, but also, places that appear [to have had] traces of water, and to try to really read the story in the rocks, and to see what conditions existed and how habitable it really might have been.”

  About the time JPL restarted Martian exploration after a lengthy post-Viking hiatus, a picture began to emerge that the Mars Exploration Rovers would be able to augment in a spectacular fashion.

  “According to previous missions, there has been abundant water on the Martian surface in the past. Now, evidence of water is not entirely credited to rovers. If you look at Mariner 9, you can see the first evidence of water channels and so forth, so we noted in the early 1970s that there was once water on Mars. But what we have been able to do is to fill in a lot of details regarding the chemistry, the kinds of processes that were going on there. This a very rough number, but for the first billion-or-so years of [Mars's] history, conditions on the surface were warmer and wetter, there was alteration going on, there were hydrothermal systems; it was a much different place than it is today.”

  By 2004, Squyres had two well-equipped rovers on the Martian surface, one on either side of the planet. One of the first discoveries, and not a heartening one, was the presence of large amounts of a rock that he wished had not been there: olivine.

  “It is a mineral that tends to be present in unaltered igneous rocks [that is, unaltered by water], so finding it was a disappointment, because that was one of the first things that made us realize that we landed on a lava flow instead of…on sedimentary rocks. We landed on a lava flow…one at least a billion years old.” And lava flows, while interesting, are much less promising for this type of exploration than something indicative of watery activity.

  “It took awhile for it to kind of sink in what we were dealing with, that the sediments we were looking for were completely buried in the lava. Once we finally realized that, we had to move somewhere else, and we decided to head for the Columbia Hills.”

  This was a geologically interesting region nearby that had been named in honor of the astronauts lost when the space shuttle Columbia broke up during reentry in 2003.

  The Columbia Hills were over two kilometers from Spirit's landing site, and given the slow rate that the rovers were allowed to move, it was a long haul. An astronaut on Mars wouldn't think twice about covering the distance; controllers driving an aging rover, which had completed its primary assignment but seemed to have plenty of life left, had to consider their options with care.

  “The rover was designed to last for ninety days, and drive over 600 kilometers [about 375 miles] in its lifetime. On day 100 of our ninety-day mission, we decided that we needed to go somewhere different, and the Columbia Hills were 2.5 kilometers [about 1.5 miles] away. We had already voided the warranty of the vehicle, and we had no idea how long it was going to last, so we just went as fast as we could. But we got there. We reached the hills on sol 156 and spent the rest of the mission there.”

  Meanwhile, across Mars, Squyres had another rover to worry about. Opportunity had enjoyed the good fortune of landing in Eagle Crater, which provided a whole different set of options.

  “The biggest discovery from Opportunity came within the first 60 sols, so we lucked out. We discovered a giant impact crater that basically had all the things that we could have wanted exposed in the wall of the crater. In two months, all the most important science was revealed to us. Since then, we've been taking advantage of the fact that Meridiani Planum is very smooth, very flat, very capable for driving, to cover a lot of ground. Our strategy is to go from impact crater to impact crater. We're driving around on layered sedimentary rocks that were horizontally layered, which meant that you're driving along a flat surface, and you're basically seeing the same rocks over and over again. So what you need is some capability to get down below the surface. Now, we didn't bring a drill rig, but Mother Nature has dug many craters for us on Mars, so we had to go to those craters and then find a big one, and go into it to explore below the surface. We [now have] something like thirty-one kilometers [about nineteen miles] on the odometer so far.

  “We're heading towards Endeavor Crater, and it is huge, [a] twenty-plus-kilometer-diameter feature [about 12.5 miles across] formed a very long time ago, before the sediments were even deposited. Pieces of the rim of the crater are sticking through the sedimentary layers, and those pieces of the outer rim are older than anything we've ever seen before. So we're closing in on the crater, all the never-before-seen materials, with an old, tired, beat-up rover.”

  Spirit has ceased to operate, but in a way it lives on within the mission of Opportunity. Soon the second rover will reach its destination, very possibly its last, and provide us with new answers and new questions.

  It's been a long haul for Squyres. There were times he wasn't sure the MER mission would happen at all: “One of the high points was, simply, the launch. I mean that very seriously. I went through ten years of writing unsuccessful proposals to NASA before they finally said yes. And then, we were flat-out canceled and brought back to life three times! When we finally were given the go-ahead to do the mission, we [had] thirty-four months to do
a job that would properly take about forty-eight, so at times it just seemed inconceivable that we would ever get to the launch pad. Just getting to Florida was a miracle; just getting a shot was a high point.

  “Then there was the day when the first rover drove off the lander and had six wheels in the dirt and we were ready to really explore. That moment was really the culmination of seventeen years of work that we had done to make that happen, and after that it was just our rovers and what Mars gave us and how well we could perform with what we had. It's just been a seven-year-long adventure with one discovery after another. To me, because of all the years of effort that was put into just making the thing happen at all, those events were the ones that affected me the most deeply.”

  Squyres falls silent after this for a moment, and perhaps it is because he realizes that it not only deeply affected him, but the rest of humanity as well.

  Opportunity's mission continues.

  It was as if everything from before had been viewed on VHS tape and the newest images were in Blu-ray®. The images from JPL's latest, the Mars Reconnaissance Orbiter (MRO), were that good. This mission was a whole new ball game in orbital imaging.

  For one thing, the cameras onboard were the best to date. The other scientific instruments accompanying them were also cutting-edge. But it was the radio dish that was perhaps the most arresting feature of the orbiting spacecraft. While the craft itself was about 1.5 times larger in size than earlier orbiters, the dish was almost as wide as the spacecraft and at least twice as wide as previous transmitters. At almost ten feet across, it was a huge jump in bandwidth. Combine this with the latest in data compression, and it was like going from dial-up to broadband in one fell swoop. In fact, by 2008, after just about 1.5 years of operation, the craft had sent home over fifty terabits of information, or more than all of JPL's planetary missions to date. That's an impressive accomplishment in anyone's book, and a bigger “pipe” by an order of ten over earlier craft.1