Curiosity Page 28

  By March 19th, they had confirmation that the B-side was back in good form, and they could continue science operations inside the rover, even as they also continued to resolve the original issue on the A-side of the computer.

  Even as the computer drama was playing out, however, the scientists had continued their work when they could, while the engineers labored over the computer. Just before mid-March I was up at JPL doing some interviews, and I ran into Rob Manning. I, of course, asked what was new, and he smiled like a kid with the biggest secret this side of Christmas: “I can't say much right now, but we think we found what we came for.” The hairs on the back of my neck stood up a bit. “Habitability or organics?” I pestered. He chuckled and chided, gently, “Wait and see,” so I did. I already knew a bit from previous interviews, but this could be something big.

  The next day came the announcement.

  PRESS RELEASE

  03.12.2013

  Source: Jet Propulsion Laboratory

  NASA Rover Finds Conditions

  Once Suited for Ancient Life on Mars

  PASADENA, Calif.—An analysis of a rock sample collected by NASA's Curiosity rover shows ancient Mars could have supported living microbes.

  Scientists identified sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon—some of the key chemical ingredients for life—in the powder Curiosity drilled out of a sedimentary rock near an ancient stream bed in Gale Crater on the Red Planet last month.

  “A fundamental question for this mission is whether Mars could have supported a habitable environment,” said Michael Meyer, lead scientist for NASA's Mars Exploration Program at the agency's headquarters in Washington. “From what we know now, the answer is yes.”

  Clues to this habitable environment come from data returned by the rover's Sample Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin) instruments. The data indicate the Yellowknife Bay area the rover is exploring was the end of an ancient river system or an intermittently wet lake bed that could have provided chemical energy and other favorable conditions for microbes. The rock is made up of a fine-grained mudstone containing clay minerals, sulfate minerals and other chemicals. This ancient wet environment, unlike some others on Mars, was not harshly oxidizing, acidic or extremely salty.

  The patch of bedrock where Curiosity drilled for its first sample lies in an ancient network of stream channels descending from the rim of Gale Crater. The bedrock also is fine-grained mudstone and shows evidence of multiple periods of wet conditions, including nodules and veins.

  Curiosity's drill collected the sample at a site just a few hundred yards away from where the rover earlier found an ancient streambed in September 2012.

  “Clay minerals make up at least 20 percent of the composition of this sample,” said David Blake, principal investigator for the CheMin instrument at NASA's Ames Research Center in Moffett Field, Calif.

  These clay minerals are a product of the reaction of relatively fresh water with igneous minerals, such as olivine, also present in the sediment. The reaction could have taken place within the sedimentary deposit, during transport of the sediment, or in the source region of the sediment. The presence of calcium sulfate along with the clay suggests the soil is neutral or mildly alkaline.

  Scientists were surprised to find a mixture of oxidized, less-oxidized, and even nonoxidized chemicals, providing an energy gradient of the sort many microbes on Earth exploit to live. This partial oxidation was first hinted at when the drill cuttings were revealed to be gray rather than red. “The range of chemical ingredients we have identified in the sample is impressive, and it suggests pairings such as sulfates and sulfides that indicate a possible chemical energy source for microorganisms,” said Paul Mahaffy, principal investigator of the SAM suite of instruments at NASA's Goddard Space Flight Center in Greenbelt, Md.

  An additional drilled sample will be used to help confirm these results for several of the trace gases analyzed by the SAM instrument.

  Fig. 29.3. ASHWIN VASAVADA: As one of two deputy project scientists for MSL, Vasavada spends most of his time overseeing the processes that get Curiosity through its scientific tasks, interacting with the 480 other scientists on the mission. He is highly prized as a public speaker for his ability to impart scientific concepts in a way that laypeople can understand. Image from NASA/JPL-Caltech.

  “We have characterized a very ancient, but strangely new ‘gray Mars’ where conditions once were favorable for life,” said John Grotzinger, Mars Science Laboratory project scientist at the California Institute of Technology in Pasadena, Calif. “Curiosity is on a mission of discovery and exploration, and as a team we feel there are many more exciting discoveries ahead of us in the months and years to come.”

  Wow. So it was official, ancient Mars would have been habitable to life as we understand it. Again, there was an indication of water, and this time, nice, drinkable water. And whatever had caused the oxidation of all that oxygen once present in the atmosphere—the reason Mars's sand and rocks are red—had not been present in the past. That was the “gray Mars” part of the announcement.

  Vasavada put it elegantly: “We delivered the CheMin examination and got the results, which was wonderful, but I think by the time we got through all the press conferences for John Klein, a lot of them involved words like oxidation and reoxidates, but the bottom line is this: Mars is red but the inside of the rock is not, and that's the evidence that we were looking for. So that's great.”

  It was wonderful, like a second Christmas and New Year's combined. But then the inevitable train locomotive—that headlight in the tunnel I mentioned—caught up with the mission: solar conjunction. The mission went mostly silent for weeks. While a steady, weak telemetry stream came back through the furious and static-laced interference of the sun, the computer people, who had just resolved their issues, fretted. From April 9 to April 26, two and a half long weeks, Curiosity would be alone.

  Solar conjunction was a quieter time at JPL—Curiosity was being monitored but was performing nondemanding activities while not driving. The rover sat parked until the solar interference ended. It gave a lot of people time to catch up, and some of them only then realized just how all-consuming the mission had been. It also gave the science teams and the drivers time to plan activities for postconjunction, and to do so armed with all the data that they had accumulated since landing. In that way, it was a blessing.

  During this time, results of atmospheric-sample analysis from SAM were released at a conference in Vienna, Austria. The conclusion was that Mars had lost most of an ancient, denser, and more oxygen-rich atmosphere long ago. Also measured over the months of operation were humidity (a first on Mars), temperature, and wind speed.

  By the end of April, Mars had moved past the sun and into the clear, so normal operations could resume. A second drill site was selected to attempt validation of the findings from John Klein. The new site, nine feet from Klein, was called Cumberland. It was chosen in part for the same reasons as Klein—flat and safe, but also because it looked like Klein and was made up of the same ingredients—right down to the gypsum veining. Any cross-contamination of the sample should be minimized. It was a good choice to verify the observations from the first drill sample.

  Cumberland did have a somewhat-different texture, though, dotted with small bumps on the surface. These were ancient concretions, which were apparently formed in water. The drill hole was sunk on May 9 and was about the same size and depth as before. This time, once the sample was in hand, the rover drove off, with analysis scheduled to take place as other observations and driving were undertaken. JPL was anxious to get started toward Mount Sharp, five miles distant. Of course, the arrival date is predicated upon what surprises or points of interest the rover comes across on its five-mile trek to the foothills. Increased autonomy would also be required to get longer drives completed each day without as much guidance from home.

  Along the way, a few locations, called waypoints, were preidentified for examinati
on. The first, an outcrop called Darwin, was again representative of flowing water. It can be a challenge to keep the public engaged when all you have is another announcement about water (*public yawn*) on Mars, but each site is a bit different and all add to the overall story. And, of course, water is a primary focus of the mission and keeps everyone involved highly engaged—how water accumulated, how it behaved, and where it went are a continually unraveling mystery. Areas like Darwin, which contain conglomerates—rocky remains of ancient riverbeds—are favorite areas for detailed exploration.

  Dawn Sumner is one of the researchers who worked Darwin and spoke of her experiences in a NASA press release: “We examined pebbly sandstone deposited by water flowing over the surface, and veins or fractures in the rock,” she said. “We know the veins are younger than the sandstone because they cut through it, but they appear to be filled with grains like the sandstone.” As if to echo my previous point, “We want to understand the history of water in Gale Crater…did the water flow that deposited the pebbly sandstone at Waypoint 1 occur at about the same time as the water flow at Yellowknife Bay? If the same fluid flow produced the veins here and the veins at Yellowknife Bay, you would expect the veins to have the same composition. We see that the veins are different, so we know the history is complicated. We use these observations to piece together the long-term history.”

  In February 2013, an interesting announcement was sent out from JPL, but this was not related to rocks…it was about the air. The SAM instrument had analyzed an atmospheric sample, looking specifically at isotopes of argon, and the results were compared with earthbound studies of meteorites. It had been long suspected that some meteorites found on Earth were pieces of Mars, based on their chemical composition. The new SAM results provided strong evidence to confirm this for some meteorites and disprove suspected Martian origins of others. The result has been, in effect, a kind of natural sample-return from Mars. The samples are very old and have traveled through space for millions or billions of years, but they are pieces of Mars and, as such, are of extreme interest. It's a chance to peer into Mars surface bits with all the sophisticated power a fully equipped laboratory on Earth can bring to bear, and without the cost of a $4 billion sample-return mission (though such a mission, still a high-priority goal for NASA, is obviously an entirely different scientific animal).

  By the end of 2013, Curiosity was driving farther and faster than before, and making great progress. Then: more issues.

  The first concerned the computer. On November 8, the computer performed a “warm reset,” which is analogous to restarting your cellphone as opposed to performing the complete factory reset. In this case, the software spotted something it didn't like and reset itself to an initial, prior state. While still performing work, the machine was effectively in safe mode again. Within two days, the error was resolved and the computer returned to a normal state. The software team thought they knew the culprit: new software had seen something in older software—a “catalog file”—it didn't like and stopped the show until things were figured out. This was exactly what it was supposed to do.

  But less than two weeks later, another issue cropped up, this one potentially more permanent. The rover indicated a “soft-short” in its electrical system, which, as opposed to a “hard short” (the kind that trips your circuit breakers at home), caused a change in voltage levels (as opposed to a shutdown). While not crippling, it was troubling and unexpected. Within three days, they knew the cause: the RTG power source hanging off the back of the rover.

  If radioisotopic thermoelectric generators have a drawback, besides scaring the antinuke crowd, it is small short-circuits—little electrical malfunctions. Voyager had endured a number of these over the years, as had the nuclear-powered Cassini Saturn probe, and it seemed to be endemic with RTGs. The electricity-producing thermocouples that surround the plutonium are not working in the kindest, gentlest environment and sometimes act up, which is apparently what happened on Curiosity. That said, the Voyagers are still voyaging over thirty-five years later and still have power, though at slowly reducing levels. On Curiosity this was certainly not a serious setback, but it warranted keeping an eye on.

  As the year neared a close, a happy result came in from analysis of the drill sample taken in Cumberland (the rover had been carrying that sample around like a brown-bag lunch since May and had taken occasional tastes since). For the first time ever, the geologists had been able to confirm the age of a rock on Mars. It landed on the timeline at between 3.8 and 4.6 billion years old, which was about what was expected. And that's a good thing, because it lets you know that your hypothetical models are on the right track. It was another example of what the onboard instrumentation was capable of, as it had measured the amount of argon in the rock, a result of potassium that changes to argon over a long time span. Almost like carbon-14 dating, except that we're counting in the billions of years. It requires incredibly precise measurements to do this kind of evaluation, and Curiosity was fulfilling its promise.

  Then in late December, halfway through its second Earth year of exploration, the first real trouble beset the rover. What started small quickly became a larger concern. The designers had known that the rover's wheels would sustain some damage as it went about its mission—remember that it's a full ton of mass pressing down onto six wheels, albeit in reduced gravity. The wheels were beginning to show more wear than anticipated—and by January 2014, a lot more wear was visible. The damage had gone from dents and pinholes to full-on rips the size of your thumb.

  The problem was the particular type of terrain the rover was crossing as it neared an area called Dingo Gap. The terrain had thousands of sharp rocks—not unusual for Mars—sticking up in an unfortunate way—they were welded to the ground. One theory opines that these rocks, which on average appear to range from about the size of a golf ball to the size of a baseball, were part of an overall rock formation that was worn away by eons of windblown sand, whittling some of the remaining material to dangerously sharp protrusions. Normally when Curiosity drives over such rocks, they might sink into the soil or shift a bit, reducing wear and tear. But, stuck in the ground as they were, the sharp rocks created what looked like a road-hazard test course just waiting to puncture a wheel.

  The rover drivers soon had to slow the pace again, being careful to pick the best and safest route. The rover drivers would stop frequently and use the MAHLI camera on the arm to photograph the wheels, which was a time-consuming operation. And even then, the damage was accumulating faster than anyone wanted.

  If you look at one of Curiosity's wheels close up, it's actually amazing how thin they are. About the size of a small beer keg, they are machined out of a solid piece of aluminum. The wheel has thick, zigzagging cleats or ridges machined into its surface. But the expanse of metal that separates these is surprisingly thin. As always, it was a trade-off between strength and weight. The wheels can sustain a lot of damage before failing, but MSL is intended to be a long mission and there are many miles of driving ahead. The punctures were certainly not making anyone happy.

  Fig. 30.1. SHARPIES: About sixteen months into its mission, Curiosity began crossing a flat area near Dingo Gap that had sharp rocks embedded in it. These wind-sculpted formations created the Martian equivalent of a series of spike strips. This image shows damage to one of Curiosity's wheels as the rover crosses the unforgiving terrain. Image from NASA/JPL-Caltech/MSSS.

  At Dingo Gap, the drivers found a different route toward Mount Sharp that appeared to have fewer wheel-eating rocks. The only issue was that the rover would have to cross a sand dune to get there, and after the trials of the MER rover Spirit, which not only got stuck in sand a few times but ultimately died in a sand patch, the people charting Curiosity's path wanted to be very cautious in their approach.

  By early February 2014, it was a fait accompli. JPL had decided that the risk was worth the reward, and Curiosity crossed the sand dune without mishap, then headed southwest into a depression and smoother ter
rain.

  The road to Mount Sharp lay ahead, and the majestic foothills beckoned.

  So, what is the sum total of discoveries and new information gathered by Curiosity since landing on Mars? Let's just say that it would fill a book far larger than this one. In fact, I have a book to my left right now, called Mars Science Laboratory, that was edited by John Grotzinger, Ashwin Vasavada, and a gent named Chris Russell. It is a collection of papers and chapters written before the landing, and is nonetheless over 850 pages long. If you can find a copy, it retails for $270.00. And no, my copy isn't for sale. Besides, there are dozens of new, postlanding papers that have been authored by the Curiosity team, with many more in the works. Each one is a colossal effort, involving a lot of time, cooperation, and, ultimately, peer review. It's a whole lot harder than writing a book like this one, and I don't envy them the task—but it's part of academic and scientific life. At the rate they are making discoveries, there is a lot of writing and peer-reviewing to be done.

  So, let's rephrase our question: What are some of the major discoveries made by Curiosity and the science team since landing in August, 2012? They are many, and in a number of disciplines. In broad terms, there are geological, atmospheric, radiological, and chemical findings. Before we look at these, a quick rundown on Martian geological history might be in order.

  As you are doubtless aware already, Mars formed when the other terrestrial planets did, at the birth of the solar system about 4.5 billion years ago, give or take a few tens of millions of years. The rocky planets formed inward of the asteroid belt, and the gas and ice giants formed outside it, beyond the so-called frost line.

  Early on, there were lots of little protoplanets wandering around our neighborhood, blobs of planetary stuff that had not yet solidified into what they are today. For about 100 million years they smashed into one another, combining and destroying each other with abandon like a teenaged demolition derby. There are, of course, various theories about the specifics, but in general terms, the resulting mess coalesced into the four terrestrial planets we now see: Mercury, Venus, Earth, and Mars. A fifth that missed the train, never consolidating, now forms the asteroid belt beyond Mars. It is the wayward, shiftless cousin of the rocky planets.