Red Rover

by Roger Wiens

  Besides the instrument leads, there was one other person at the head table who was to be in charge of all of us. JPL staffed an office for the “mission scientist,” the scientific head of the project. This position was initially held by a JPL official who we knew would retire well before launch. So about a year into the work, I got a call out of the blue from Professor Ed Stolper, who had been the chairman of the Caltech Geology Department when I was there. As a younger scientist, I had looked up to him back then, but, a number of years my senior, he had seemed to be such a difficult man to impress. I was still rather intimidated by him, so after an awkward pause over the phone, instead of greeting him, I blurted out, “A voice from my past!” The equally awkward response came back: “It’s going to be a voice in your future!”

  Ed proceeded to tell me he had been appointed as the new Curiosity mission scientist. He ended up holding the position only a couple of years. When Caltech called on him to become a provost, he relinquished the mission-scientist role. It was taken over by John Grotzinger, another very capable Caltech geologist. John had been on the MER science team, so he already had firsthand Mars experience. He was a very personable leader and an excellent teacher who exuded fascinating details about geology at every opportunity. It was a delight to attend field trips and meetings under John’s capable command.

  Over time, the rover leaders got to know each other better. We knew that our fates hung together. If the project were to be canceled or the spacecraft were to crash, we would all miss our chance to visit Mars. And so we supported each other. It was this inner circle that helped rescue ChemCam when Dr. Stern had tried to cancel it. We went through a few other challenging times, but mostly we worked together to lead our respective instrument teams.

  Well before the instruments were completed, the whole MSL science team participated in a group exercise to learn to work together. In 2007, we embarked on an activity called the “Slow Motion Field Test” to familiarize everyone with the new techniques available on Curiosity and how we would use them jointly to determine the geology, and possibly the biology, of the landing site. We were to pretend that Curiosity, which had not yet been built, was in some unknown location on Earth. Once a month we would carry out one day of pretend operations, hence the name “slow motion.”

  On the first Mars day (sol), the team had only images to view. We got a satellite image to show the general terrain, and a panorama so we could see the surroundings. Using these, the team was to decide where to send the rover over the next several sols and what types of analyses should be done with the rover’s “tool kit.” Each month, after the next sol’s plans were made, the JPL science office sent out “the rover,” a geologist by the name of Ralph Milliken, to take new pictures based on where the team had “sent” the rover.

  Ralph also gathered representative rock and soil samples and mailed these to the various labs. Instruments like those being built for Curiosity would then analyze the samples and provide data for the group. To make sure no one cheated, the organizers asked that someone not associated with Curiosity operate the instruments and send the data to JPL. They were particularly curious about ChemCam, as they had never dealt with a LIBS laser before, and they were a little suspicious that it might not live up to our claims. This was our moment to prove ourselves.

  I was not at all sure we were ready for this test. It was just two years after starting the project and we were in over our heads dealing with design and construction details. Not much attention had been paid to getting accurate results back in our lab. After the laser accident and shutdown of 2004, Sam Clegg had assumed responsibility for the analytical work. Although Sam was an excellent scientist, he had started with absolutely no experience on LIBS. Two years was a very short time to learn all of the intricacies of the new technique, let alone to learn about Mars geology. Besides, he was only working on ChemCam part-time.

  The dominant rock types on Mars are volcanic basalts, much like the type of rock under the Earth’s oceans. Except for the 2003 Opportunity rover, which ended up among sedimentary rocks, all of the landings on the Red Planet had taken place in basaltic areas. Basalts were much simpler to characterize, and so we had focused on them. They are made up of 50 percent silicon dioxide, with the rest made of iron, aluminum, calcium, magnesium, and a few other elements, all of which gave good signals in LIBS. We had just finished a paper comparing different basaltic meteorites from Mars, and the results had come out quite well, which had given me at least some confidence that we should try to participate in the Slow Motion Field Test.

  We were to have LIBS analyses for the “second day” of the test, scheduled for one month after the first day. Though the ChemCam-like data were obtained in our lab, we were to receive it off the JPL website just as if they were results from Mars. We would be given one day to look at the numbers. Then we’d have to present our findings to the whole team of well over fifty people on the phone and Internet. On the morning the data were made available, I got a call from Sam.

  “Roger, do you have a minute? We have to talk about the ChemCam data!”

  I could hear real concern in his voice. I had not looked at the data yet. He wanted to come up to my office rather than talk on the phone. His office was several miles away across the sprawling Los Alamos lab complex. While he was driving over I cleared my desk and started to pull up the new data. Sam burst in the door, shut it tight behind him, and sat down.

  “There’s no silicon in these data . . . none of the samples!” he blurted out, still out of breath. All of the rocks Sam had worked with so far had been basalts, which were always silica-rich. We had instructed James Barefield, who obtained the data for this test, to use basalts as standards by which to compare the new samples, hoping the mystery rocks would be similar. Clearly we had anticipated the wrong kind of rocks!

  I thought back to the rover field test we had missed because of the fire. We had later analyzed samples that were sent to us from the field location. Some of those samples had been carbonates. On the Earth’s continents, the dominant sedimentary rock is carbon-based, like limestone, which is usually produced from organic matter. But I didn’t expect carbonates in a simulated Mars field test, because no such rocks had been discovered on that planet. Further, I had assumed the field site would be relatively close to JPL in Southern California, which is poor in carbonates.

  I looked in the location on the chart where we should see the carbon emission peak, and sure enough, there it was in some of the samples! I pulled up some old data and confirmed that our mystery materials looked like dolomite, a variant of limestone. Sam breathed easier. This was actually going to be quite fun. Scientists had been speculating about and looking for carbonates on Mars for the past three decades. We could pretend to have discovered carbonates on Mars.

  Sam, being more analytical than I was, scanned the data carefully. He was now thinking outside the box, too, and he noticed that several other mystery samples did not have a carbon peak, and although no new elements showed up, the ratios of some of the peaks clearly looked different.

  “These couldn’t be sulfates, could they?” Sam queried in wonder.

  Gypsum is a common sulfur-bearing sedimentary material. Unfortunately, LIBS is not very good at detecting sulfur. Neither of us had any experience with this element, but we knew that lots of sulfur existed on Mars. We consulted a database of emission lines and found where the sulfur peaks should be. Yes, we saw some faint peaks! But we couldn’t be sure they were sulfur. We suggested in our write-up that we might have observed sulfur, and Sam vowed to start experimenting with sulfur-bearing rocks as soon as he got back to the lab.

  We had a great time presenting the data to the eagerly awaiting team the next day. Given ChemCam’s role as the remote sensing instrument, it gets to make the first chemical analyses, and the rover had not yet used its arm or other instruments in our pretend exercise. The team members received only pictures and the ChemCam report. To go along with the simulation, our report started out with a big
banner saying, “Press Release: CARBONATES FOUND ON MARS!” We pointed out the spectral features showing carbon, oxygen, calcium, and magnesium—the only major elements present in these rocks. We also suggested that we had observed sulfur in the other samples.

  Everyone was excited about our imaginary press release, and over the next several days, the team enthusiastically picked new targets on the rocks for ChemCam to shoot at. For the next simulated day of the rover exercise, a month later, we showed definitively that the two types of rocks in our field area were carbonates and sulfates. We had proven ourselves!

  The field site turned out to be in southern New Mexico, far from JPL, and on the edge of the sedimentary basin that spans western Texas, the richest oil field in the continental United States. The Curiosity team later took a field trip to visit the site. We were able to see the alternating layers of carbonate and gypsum identified in our Slow Motion Field Test, the same materials that produced the famous dunes at White Sands, New Mexico. In the meantime, a carbonate rock was found by the Spirit rover on Mars, making the field site all the more relevant to our work, but beating us to the discovery on Mars.

  chapter

  twenty

  WHERE ON MARS?

  DURING THE FIRST SEVERAL YEARS OF THE CHEMCAM PROJECT, we were so focused on getting the instrument built and operating that it was difficult to spend much time considering our destination. The first opportunity to turn our attention to Mars came in June 2006 at a landing-site workshop. This was the first in a series of five such meetings that would be devoted to finding the best place to carry out the rover’s investigations on the Red Planet. As busy as I was with ChemCam, I arrived a day late and still spent much of the time on the phone with contractors and vendors of optical parts that we needed.

  The workshop was held over three days in a crowded room at the Pasadena Convention Center. The meeting was open to anyone, not just the Curiosity team. Although many of the attendees were veterans of the two previous generations of Mars rovers, notably absent were the MER science leaders Steve Squyres and Ray Arvidson. Their absence represented the shift in leadership for the new mission. The assembly was clearly excited at the prospect of a new site to explore. But with a total land area equal to that of Earth (not counting the oceans), Mars presented a huge number of possibilities for this one new opportunity. The fact that Curiosity was designed to land within a relatively small ellipse opened up many new potential sites that had not been available to previous missions.

  On the first day of the meeting, NASA’s planetary protection officer, John Rummel, laid the ground rules for types of locations that could not be considered because of the risk of seeding Mars with terrestrial bacteria from the nonsterilized spacecraft. With its thermal source in the RTG, there was a possibility that if the rover crash-landed in a place with lots of ice, heat from the rover could create a semipermanent puddle of melted water slightly below the surface that could allow terrestrial bacteria from the rover to survive indefinitely. The same thing could happen if the rover eventually died of old age while traversing an icy area. So the project was not allowed to target icy areas. As a result, some of the most interesting places—recent gullies thought to be produced by running water, for example, and some apparent glacial features—were off-limits for Curiosity. Other issues, such as strong crosswinds or steep terrain, which could result in excessive risk at landing, caused some other desirable sites to be crossed off the list.

  However, these details did not dampen the spirits of the crowd. In fact, I had hardly ever seen such jovial scientists. We were in our element! In true American spirit, the meeting ended with a vote on the favorite landing sites. The votes were tallied, and some final words were spoken about the plan forward. The next meeting would not be for another fourteen months. In the intervening time, the spacecraft orbiting Mars would get close-up views of the favorite landing sites, providing new information for the next meeting. For now the Mars community was happy that the planning for the ground campaign had begun.

  At the second workshop the community took up where we had previously left off. A lot of effort was focused on the top seven sites as scientists investigated new imaging data to see if our hopes and dreams for these places were realistic. With only a few locations to consider, the discussions became a little more heated. In the end votes were again cast. As an afterthought, some of the organizing committee called in a few engineers to reassess the technical feasibility of the sites. This “morning after” team pronounced doom on Nilli Fossae, a large valley in Mars’ northern hemisphere: it was too risky to land there, because of its relatively high elevation and other factors. The site’s promoters fought the ruling, but to no avail. Another site seemed to rise from near obscurity to become a favorite. The Mars Reconnaissance Orbiter’s (MRO) new analyses revealed very interesting clay layers near the bottom of Gale Crater, a large impact feature right on the boundary between the ancient southern highlands and the relatively featureless northern lowlands. The clay and what appeared to be shorelines guaranteed that the team would be able to study a location that had standing water for a reasonable period of time. Not only that, but Gale was host to a mound of sedimentary layers taller than the Grand Canyon. Because there was no evidence for currently existing ice there, the site had the green light from NASA’s planetary protection office. This might be the “habitable environment” we were looking for.

  By the end of the next meeting, four sites remained on the list: Gale Crater, two other crater sites having very interesting streambeds and river deltas, and a very ancient site, Mawrth Valles, which, out of the four, was the one displaying the strongest clay mineral signature from the French Visible and Infrared Mineralogical Mapping Spectrometer (OMEGA) on the orbiting Mars Express and from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the MRO.

  When the launch delay was announced in late 2008, the community suddenly had an additional two years to study the sites. The first thing that happened was to reopen the field, in case recent orbital images had revealed any new top sites. New candidates were put forward, but after several committee meetings none of these was deemed more interesting than the original four—we had apparently done a good job of narrowing down the field in the first place.

  It was clear that the four sites appealed to different types of interests. Those who studied mineral signatures from orbit—the spectroscopists—wanted the site that showed the strongest spectral signatures, which was the ancient Mawrth Valles. The people who studied physical features in the images—the geomorphologists—wanted places that showed the most interesting shapes and details, including features resembling river deltas, shorelines, and sedimentary rock layers. Mawrth Valles didn’t have any of these features, so to the geomorphologists, that site seemed boring. Many of the interesting visible features—the possible deltas, shorelines, rock layers, and riverbeds that attracted the geomorphologists, however, didn’t seem to have strong spectral signals, and therefore did not interest the spectroscopists. The spectroscopists questioned the value of exploring any area that didn’t have clay minerals in them, because they viewed clay minerals as the starting point in the search for evidence of biota. The geomorphologists suggested that the clay minerals could be buried by dust at these sites, so the team should consider them anyway.

  We really needed two rovers to satisfy everyone. Unlike the MER scientists, we only had one.

  The Mawrth advocates were led by Jean-Pierre Bibring, a charismatic and very vocal scientist who had led the mapping of Mars from orbit with his OMEGA instrument several years earlier. Bibring, with long, thinning white hair, a deep forehead leading to a pointed nose, and somewhat outdated French clothes, looked like he could have jumped a time machine from the Revolution. He had “interesting” political notions that, fortunately, he did not discuss often. At any rate, he was one of the top planetary scientists in France and certainly the most outspoken. Based on Bibring’s discoveries, the Mawrth site clearly had more than one type of clay
mineral, and it was also the most ancient location being considered. There was a relatively large group of French scientists at the landing-site meetings, and in the Curiosity team in general. Normally, the French come across as fiercely independent, but interestingly, every single compatriot seemed to line up behind Bibring. I had never seen this solidarity among his colleagues. Some non-French scientists reacted quite negatively to the unanimity of the French scientists. Why should the French, usually an independent lot, try to vote all in one block?

  Two landing-site meetings were scheduled in the final fourteen months before launch. We did not want a stalemate going into the final meeting. The first of the two gatherings took place in late 2010. Presentations were finely polished. Discussions over mealtimes and at breaks became intense, but no site appeared to rise above the pack. Voting was no longer employed, as we did not want one or two votes to decide the whole outcome. Instead, the debate closed with statements about each of the four candidates. It was going down to the wire!

  The final meeting, in May 2011, was to be a marathon. We had scheduled a workshop for the ChemCam team over the weekend to take advantage of colleagues coming from France. After that were three days of community landing-site discussions, then a morning with attendance narrowed down to only the Curiosity science team, and finally an afternoon with only the inner circle cloistered.

  At the beginning of the week, John Grotzinger, our project scientist, approached me with thoughts about how to bring about a decision. It was up to John to get us past this issue and on to the mission itself. I suspected that John’s preferred site was Gale Crater, with its 5-kilometer-high sedimentary mound and its canyons, inverted stream channels, and alluvial fans, but he was not telling this to the science community at large. John was our leader, but he didn’t want to force his will on us.