Destination Mars

by Rod Pyle

  One thing led to another, and as the fraternity of planetary explorers is a close one, Soderblom's next stop was the United States Geological Survey. “I actually joined the USGS in 1970 when I finished my doctor's degree, and I went to work for Hal Mazursky, [who] was the lead of the television experiment on Mariner 9, [which was] the first spacecraft to orbit another planet. We ended up mapping the entire surface.”

  That accomplishment was not an easy one even under ideal circumstances. When Mariner 8 was lost, it became much more difficult. “It was a scramble, because [Mariner 8] was [to create] a global map, to systemically map the planet. [Mariner 9] was an orbit that allowed repeated coverage of particular areas, to look for changes or activity, and the two orbits were quite different so they had to be blended together to satisfy both goals.”

  Of course, as Mariner 9 neared Mars, it was clear that the mission of the remaining spacecraft had just become still more challenging…the planet was enshrouded in a dust storm of global proportions.

  “As a matter of fact that [dust storm] was kind of fun, because I noticed very subtle darkish patches in the cloud. I worked with the people at image processing and we invented a special filter, [because] we just couldn't see anything. So we ran [the filter] over the images and out popped four gigantic volcanoes! We knew [they] had to be really tall, to poke up through the dust cloud. The Martian scale height is about 30 kilometers [18 miles] and the dust, if it's mixed uniformly, which would be in the lower atmosphere, wouldn't drop to 30 percent of your level. So you get to thirty thousand feet, it had to be quite high. They were big, big volcanoes.”

  Eventually the storm abated, but it took time for the view to reach its full magnificence. “It clears gradually over many months; [the dust] takes a long time to clear the atmosphere. When it did, we started to see contrast in the polar regions, where there was ice on the surface that would stand off, and started to sublime and clean up. Of course, it never clears up completely, but it clears as much as it ever clears. There's always haze in Mars's atmosphere. But [the storm] cleared to the point that we could see as much detail as the camera would permit.”

  Mariner 9 replaced the few images sent back by the rapid flybys of the past with a year of orbital photography, and some surprises were inevitable. “We realized what Mariners 4 and 6 had suggested to us was that Mars was heavily cratered with an ancient surface. [When Mariner 9 arrived], and as the dust cleared, the channels, all of the fissures and streaks, the interpretation had swerved from being a very ancient dead Mars back to an exciting and complex, albeit desert, environment. That was the big realization. It was quickly apparent that there was likely flowing water on Mars, and that was in some of the Mariner 9 data.

  “It was then that we understood: Mars was not just the moon painted red.”

  And perhaps that is the most elegant way of summarizing the profound nature of the Mariner 9 mission. It was a game changer. For while the previous Mariners had given us our first glimpses of this mysterious world, Mariner 9 gave us its true face…and what a face it was. The framework was now in place for a great leap forward—a robotic landing on Mars.

  Viking had been planned from the start to search for extraterrestrial life—in this case, Martian microbial life. Toward this end, and after long and rigorous debate, a suite of investigative and highly portable experiments had been designed. Ingenious in their overall concept, simplicity, and execution, the suite was robust yet straightforward in its design.

  The life-science experiment could be thought of as a man locked in a windowless room. We, as outside observers, have no idea if anyone is inside. This room may have no windows and no doors, but it does have a fancy mass spectrometer affixed to the only air exit from the room (bear with me here), and we are monitoring the mass spectrometer. The man eats some Italian food, heavy on the garlic. After he finishes the meal, give it a few hours…he might even pop a few Tums®…but eventually, he will probably emit a satisfied burp. Since the room is sealed, eventually the vapor from his emissions will make its way to the spectrometer. It will sense the compounds in his gaseous outpouring, and via this we will know that there is a man in the room, and have some idea of what he ate (and then we'd best let him out, as the air is getting mighty thin and smells like garlic!).

  This, in simplistic terms, is how the Viking life-science experiment was intended to work. In reality it was much more complex. Now, imagine that a group of such rooms aboard the small spacecraft: the supply of Italian food and the instrumentation for four different experiments had to be reduced to a package far smaller than a cubic yard and weigh less than thirty-five pounds. That was the challenge facing the designers of Earth's first flying life-sciences lab.

  But before they could utilize their amazing machine, they had to decide where to land. Given that their only resources to date were fuzzy telescopic images and data from Mariners 4, 6, 7, and 9, they did not have a lot to go on. So the drama of landing-site selection is a story unto itself, for nobody wanted to be the one person responsible for sending this billion-dollar mission to a lander-wrecking Martian rock quarry.

  Mariner 4 had imaged scarcely 1 percent of the Martian surface…6 and 7 had added to that, performing detailed mapping of about 20 percent of the surface. But there were still vast regions of terra incognita (or perhaps more properly, Ares incognita) unseen and unmapped. Then Mariner 9 covered most of the planet at some level of quality, but mission planners could be not be entirely sure just what they were seeing, as the resolution was not very high; anything smaller than half a mile in size was invisible. It would be easy to miss a threat the size of a small city block: a huge crater, an enormous outcrop, or a rock-strewn field. And to make matters worse, there was one huge factor mission planners did not know: Mariner 9's pictures were not even as good as they thought.

  When the dust storm that met that spacecraft settled, it was assumed that the images taken once the air cleared were the best that could be obtained by that camera. What the Viking planners could not know was that there was still an immense amount of dust in the air, softening every image they took. It was like having a silk stocking pulled over the orbiting camera lens, and the pictures were somewhat diffused. But to the folks on the ground, they looked just fine. Nobody would realize how degraded the images were until the Viking orbiters began shooting better pictures upon their arrival in 1976.

  Also in play were the primary goals of the mission: to examine the soil on Mars for life-forms or prelife organic compounds. This goal affected landing-site selection more than anything except for concern about a safe landing. Would they be more likely to find life near an old water-carved feature? Near the poles? Mars receives intense solar radiation, despite its distance from the sun, and there was concern about the sterilizing effects of this on the soil. And the sampler arm, miracle of engineering that it was, could barely scrape a few inches into the soil, so it could not dig deep to find buried (and therefore possibly protected) microbes. It was a thorny problem, and it shows a bit of insight into how every element of such a mission has the potential to explode into a huge debate. This element did.

  Leading up to the Viking landing-site decision, and after the demise of Mariner 9, the scientific community organized the “Planetary Patrol.” Working with observatories like Lowell Observatory in Flagstaff, endless observations of Mars were made and reams of data examined in an effort to track cloud formation, dust storms, and anything else that could be gleaned from the limited abilities of Earth-based observing.

  Viking planners were also hoping for images coming from the Soviet Union's planned missions for 1973. Between orbital and, perhaps, surface photography, the NASA people might be able to gather some more data for Viking's cause. But these flights failed as had their forebears, and little data was returned—nothing at all of value to the Viking team.1 The Americans would have to continue to stay the course alone.

  So another element was thrown into the fray: radar. Using the largest radio dishes in the world, capped by t
he huge dish at Arecibo, Puerto Rico (a natural crater with a radio dish built in) they bounced radio waves off targeted areas on Mars. It was just one more way of identifying smooth (and, therefore, presumed safe) areas on Mars for landing-site consideration.

  In the end, they would have to wait for images to come down from Viking's own orbiter cameras to make a final decision. This was cutting it close, but because the lander computers were somewhat reprogrammable, it was considered a worthwhile risk. Once the orbiters arrived at Mars in mid-1976, they immediately began sending back images of the surface below. And while they were spectacular, with resolution an order of magnitude better than Mariner 9's, there were a few surprises in store…not all pleasant ones.

  One of the early landing-site candidates, a region called Chryse, had been selected after years of debate over the Mariner 9 images. It was an apparently flat, safe plain. But when the Viking images came through, Chryse revealed itself to be a rough, heavily incised riverbed. Filled with islets, craters, and channels, this was not the bedsheet-smooth area they had gambled on. To make matters worse, previous photographs had led photogeologists to theorize that Mars did not have many smaller craters. They were wrong, so very wrong. Much like the moon, it was filled with pockmarks of all sizes, from tiny to immense. Everywhere they looked, there were dozens, then, as one got closer, hundreds of them—any one of which was capable of wrecking the small landers. Hearts sank when the complexity of the terrain became evident.

  In fact, this being the 1970s and with computers still an expensive luxury, a corps of graduate students over at Caltech (just a few miles from JPL) were pressed into service doing extensive “crater counts” from the Viking images in an effort to extrapolate what the nearby terrain might be like. It was an all-hands-on-deck effort.

  Soon, after vigorous debate, the landing area was moved to a nearby region known as Chryse Planitia (Golden Plain). But once the photographic determination had been made, the ongoing radar survey showed that this region too was more hazardous than thought. The debate raged on until the last few days before landing, when a decision was reached. Chryse Planitia would be Viking 1's landing spot.

  This left a decision to be made for the second lander. Site suggestions had ranged from the far side of the planet to the polar regions. And of course, once the macro decision was made for a region, the micro work began, attempting to assess the smaller dangers within. The area finally selected, through a similarly grueling process that lasted, again, until shortly before a commitment to landing, was Utopia Planitia (the Nowhere Plain), inside one of Mars's largest impact basins, and almost directly opposite Chryse Planitia on the other side of the planet.2

  The torturous selection process for landing sites was almost alchemy; as much intuition and kismet as science and fact. And much the same can be said about the design of the life-science experiments, Viking's raison d'être, to which we now return.

  One of the largest challenges facing the designers of the Viking life-science experiments was to determine what kind of life, what form of life, was relevant to seek out. How similar to terrestrial life-forms might any life on Mars be? This was the late 1960s/early 1970s, so the hardy life-forms that exist in places like the Atlantic seabed's hydrothermal vents had not yet been discovered and certain assumptions had to be made based on the state of the biosciences at the time.

  The final design of the life-science experiments all depended on organic compounds in presumably benign Martian soil reacting to something. That something could be heat, light, and/or nutrients. And while from today's perspective the Viking package looks almost quaint, for its time it was an amazing piece of compact engineering, and the fact that it performed the tests it did successfully, regardless of the results, is astounding.

  Each experiment within the suite had an individual container with associated heating elements and other apparatuses. Individual containers were fed soil from the sampler arm, which extended from the lander, scooped up some Martian dirt, then retracted and dumped the dirt into the experiment's container. It was all very high-tech for 1976. The experiments in question were:

  The Gas Chromatograph/Mass Spectrometer: This device would sort through elements within a vapor given off when the soil was heated and then specifically identify them via molecular weight.

  The Gas-Exchange experiment: This oven analyzed gases given off when a sample of Martian soil was “cooked” after having been fed a dose of chemical nutrients with water added. It looked for the hypothetically resulting metabolized gasses.

  The Labeled-Release experiment: This device fed a small amount of nutrients to a soil sample, which were “tagged” with radioactivity, in this case carbon 14. The device looked for the release of radioactive CO2 as a by-product of metabolization.

  The Pyrolitic-Release experiment: This also utilized carbon 14 to measure possible photosynthesis. Light and water were added to the C14-laced atmosphere inside the experimental container. A period of theoretical growth was allowed, then, after the Martian “air” was evacuated from the chamber, the sample was burned to see if any of the C14 had been retained through photosynthesis.

  Again, certain assumptions had to be made to move forward. One of them was the recipe for the liquid nutrients that were squirted into each of the experiments that needed them. The final solution used has often been described as a “chicken soup”-type fluid, the design of which was based on an Earth-based understanding of life. It was a noble effort. Other experiments used simple water.

  Once the Viking 1 lander had succeeded in reaching the Martian surface, its first tasks were to create two images and conclude whether it was safe enough to proceed with its research program. Then the life-science experiments, weather observing operations, and the rest would have begun. But concerns over successful communication with Earth, about twenty light-minutes away, had resulted in the onboard computer, a for-the-time advanced 18-kilobyte (18k) unit, being programmed in such a way that if there were a failure to communicate with Earth, the lander could operate automatically. It would theoretically complete its primary mission without ground intervention for almost a month, sending data one way toward Earth as it proceeded. Fortunately for all concerned, the communication link among the lander, the orbiter, and Earth worked fine, and the probe did not have to be self-directed.

  You might expect the first photograph from the lander to be of the dramatic, far-off Martian horizon. Indeed, many working on the mission would have agreed with you. But before the lander would image the horizon, JPL wanted to know what it was sitting on. After all, controllers had just experienced a three-hour-plus blind landing and were on the wrong end of a twenty-minute delay in receiving data. The first image would be not of the weathered Martian horizon, but of a footpad.

  And what an image it was! As previewed in chapter 1, the slow, strip-by-strip buildup of that first view of Mars was a suspenseful, thrilling moment. As the image was assembled on the giant video screen, one vertical strip at a time, it revealed pebbly, rocky soil, with a portion of the lander's footpad to the right.

  The next image was a better press moment: a 300-degree black and white panoramic of the horizon. While Chryse Planitia may not have been the most daring landing site, it was still a dense tapestry of rocks, sand, and typically Martian elements, and would give geologists sufficient data to argue over for years. The next day, a color image was sent, and earthlings finally saw Mars for what it is: a fantastically alien environment with hauntingly familiar elements. We know that it is not home, but we can imagine it as such.

  The early color images had problems, however; the sky appeared to be an earthly blue and the soil reddish-pink. Later, more highly corrected imagery shows a salmon sky and an orange-ish landscape. There is art as well as science in the discipline of planetary image manipulation, and it took those image-processing experts, pioneers in dealing with color images from space, a while to get it right.

  Unfortunately, JPL was under extreme pressure from the press to get the color images ou
t. What should have taken a week of color calibration was done in hours, and the sky hues were off. When the corrected version was later presented with a properly adjusted pink sky, the press corps booed. Some asked, tongue firmly planted in cheek, if the sky might be green tomorrow. It seemed that there was a strong desire to see Mars with a sky much like Earth's; not some alien tone of pink.

  The scientists were dumbstruck. It had never occurred to anyone involved how important the images from Mars would be to people at large, nor the intensity of the emotional reaction to them. It was a PR lesson well learned that would pay off in later missions to the Red Planet.

  During these early phases of the Viking lander's mission, a meteorology boom had also been extended, and it began what would be over six years of Martian weather reports. The suite of instrumentation was designed to track the minutest qualities of the Martian day and night.

  The values of the Martian atmosphere were confirmed: quite thin, at about 0.09 pounds per square inch (PSI) (compared to Earth's 14 PSI). This thin veil is composed mostly of carbon dioxide.

  Lacking the weather-altering influence of oceans, or indeed any standing water, Martian weather turned out to be fairly predictable. The average temperature was -67°F, with a rare high of about +70°F and an equally rare low of -250°F (at the poles). Viking was able to measure much of this variation over a span of years, yielding very consistent results. At the lander's location in Chryse Planitia, the range was a comparatively moderate -22 to -139°F.

  The thin Martian air changes temperature quickly when exposed to the sun, and with no oceans to break up the vast deserts, the resultant winds can be fierce. And these often become raging dust storms dwarfing any in the solar system, as witnessed by Mariner 9. Wind speeds measured by the Viking landers averaged about 10 mph and peaked at about 70 mph, though much higher speeds have been hypothesized for other parts of the planet. But with the very slight density of the atmosphere, the effects of even these high winds are much less than an equivalent speed on Earth—about a tenth as much.