Destination Mars (10 page)

Despite this unfortunate end, the science and discoveries of the Viking program would benefit future missions and fuel the next giant leap in Mars exploration: wheels.

T
he year was 1936. The first episode of
The Green Hornet
was heard on WXYZ radio in Detroit. The first radioactive element was produced synthetically. Adolf Hitler announced the first Volkswagen Beetle®. And Norman Horowitz arrived at Caltech in Pasadena, California. It was the beginning of an auspicious career at both Caltech and the Jet Propulsion Laboratory. He was a biologist by training, but his eyes was trained on the stars…and in particular, the planet Mars.

“By 1959, it was definite that the Jet Propulsion Laboratory was going to be a planetary science lab, and people began coming down [to Caltech] from JPL to see if there was any interest here in planetary exploration.

“I thought [life on another planet] was a plausible idea. Everything that was known about Mars at that time later turned out to be wrong, but [at the time] suggested that there was a good possibility of life on Mars. I had a choice of going into something…taking this golden opportunity to get involved in a new program. And that's what I did. It turned out to be very exciting. Of course, we didn't find life on Mars, but I'm glad I did it.”
¹

Horowitz made a decision then and there that would affect not just his life, but the entire search for life on Mars. His move to JPL placed him in the Center for Planetary Exploration, where he would become one of the lead members of the Viking life-sciences team.

“The exploration of Mars became the key idea for a planetary program, for obvious reasons, and JPL set up a bio-sciences section to plan for the biological exploration of Mars, with an eventual lander. They asked me to come up and be chief of their section, which I did in 1965. There was a lot of work going on up there in trying to design instruments to fly to Mars for a biological search, and I got involved in that planning. Two of the instruments that eventually flew on Viking came out of that group. The Gas Chromatograph/Mass Spectrometer, which was probably the most important single instrument on the lander, was designed at JPL.

“When I went up there, that was already in process—it had been anticipated that this would be a useful instrument to have on Mars. What I did get involved with in connection with that instrument was making sure that there was a lot of ground-based experience with it. The instrument is based on empirical patterns of breakdown of organic compounds. You take an organic compound and you heat it until it pyrolizes—it breaks into smaller fragments due to the heating. These fragments can be identified by a combination of analytical steps called gas chromatography and then mass spectrometry. The only thing you have to identify the original compound you started with is the pattern of its breakdown products, and you try to infer the nature of the original compound from these breakdown products. There's not much general principle or general theory you can go on; you just have to have a library of results you can compare your actual results with. We did a lot of that during the years that I was there.”

And this was the key to the search for life on Mars—trying to find a way to identify the building blocks of life by remote observation. To do this, Horowitz's team would have to build up a large database of similar reactions working here on Earth. It was not a trip to Mars, for which many of them would have gladly gambled their lives, but was the next best thing to going there.

“Another thing I did was to get the idea for the second biological instrument that JPL had on the Viking lander. NASA called
it the pyrolitic release experiment; we used to call it the carbon assimilation experiment. It was an experiment that I developed with two collaborators, George Hobby and Jerry Hubbard. The point of this experiment was to carry out a biological test on Mars under actual Martian conditions. It's hard to convey in a few words the total commitment people had in those days to an Earth-like Mars. This was an inheritance from Percival Lowell. It's amazing: in pre-Sputnik 1 days, in fact, up till 1963, well into the space age, people were still confirming results that Lowell had obtained, totally erroneous results. It's simply bizarre!”

And that was the challenge. Horowitz knew by the time he moved to JPL that Mars was not Earth-like in ways that counted toward supporting life, but sometimes he felt that he had trouble getting others to understand it. Oh, they might pay lip service to the thin atmosphere, the extreme temperatures, and the voluminous solar radiation, but living deep in their hearts was a very different image of the Red Planet.

“A lot of people thought Venus was covered by an ocean. But that was speculative; in the case of Mars, they were making measurements and coming up with the wrong answers. Measurements were made on the 200-inch telescope by…a well-known astronomer—and they were completely wrong. This is just one example. And this was all based on the desire of people to believe that Mars was an Earth-like planet. It wasn't until 1963 that this began to unravel; the first step in the de-Lowellization of Mars occurred in 1963.

“[That] was one infrared photograph taken at Mount Wilson. It was an unusually excellent photograph, showing the infrared spectrum of Mars. It must have been a very dry night above Mount Wilson, a very calm night. They got this marvelous single plate, and it was interpreted by Lew Kaplan, who was at JPL, and Guido Munch, who was a professor of astronomy here…and Hyron Spinrad, a young postdoc working on Mount Wilson at the time. They showed, first of all, the total atmospheric pressure on Mars….”

But even the coldest scientific data must meet with an emotionally charged challenge when presented to the broader community, and history had something to say about the subject: “Back around 1900 Lowell had estimated [Mars's atmospheric pressure to be] 85 millibars…so when the space program started, it was generally accepted that the surface pressure on Mars was 85 millibars, and that carbon dioxide was a small fraction of this; the rest of it was assumed to be mostly nitrogen, as on the Earth.

“So at least [life] was plausible. The Martian environment appeared to be Earth-like, but a very cold and dry Earth-like environment, an extreme form…with all the same elements, with water available and enough pressure so that liquid water could exist at least transiently on the surface. This was a difficult point, to get enough liquid water to support life. With 85 millibars, there was a possibility that you could have liquified water, at least for part of the day.”

But the soon-to-be-infamous Mount Wilson data showed something very different.

“[Kaplan, Munch, and Spinrad's] findings showed that the surface pressure could not be 85 millibars. It looked more like 25 millibars to them. They also identified water vapor in the spectrum; that had never been seen before. They found very little water. And it was obvious that carbon dioxide was a big portion of the atmosphere and not a minor portion.

“Well, this turned out just to be the first step. The next big step came in 1965, when Mariner 4 flew by Mars and found that the surface pressure was more like 6 millibars! And that is the average pressure. And carbon dioxide is the principle gas in the atmosphere. Well, with 6 millibars, there's virtually no chance of having any liquid water.”

By now the great Martian cities and canals and pumping stations of Lowell and others had died a quick and merciful death at the hands of Mariner 4. But there was still a chance for something
smaller, more simple, and more realistic: “There was [still a possibility for life]. The main point up until Viking was water. And there were enough theoretical mechanisms for getting some water of the surface of Mars to maintain the remote possibility—although by the time we launched Viking, it was very remote—that there were either pools of brine or, after snow or frost there might be enough meltwater at sunrise to sustain a population of microorganisms…. [T]he real interest was in the possibility of having microbial life.”

But, though the discoveries spoke loud enough for Horowitz and others like him to hear and adapt, it was a challenge to change the thought patterns of the broader scientific community.

“In spite of all these new discoveries, people were still building instruments to fly to Mars that were based on the terrestrial environment, and they were eventually approved by NASA. NASA was supporting these efforts. Around 1960, I got involved in one of them, one that actually later flew on Viking. We called it Gulliver at the time. It was invented by an engineer in Washington, named Gilbert Levin. It depended on an aqueous medium. Two other experiments that were being supported by NASA also involved aqueous solutions into which you would put the Martian soil and then use various ways of measuring the metabolism of the organisms. But after 1965, after the Mariner 4 flyby, it was obvious that the chance of liquid water on Mars was so remote that one had to plan for the contingency that there was no water—that if there was any life on Mars, it was living under conditions that were in no way terrestrial. So we designed an experiment that would work under Martian conditions and that involved no liquid water.”

Old notions die hard, and the persistent idea of some kind of earthly life on Mars was no exception: “I think most of [this] was [because] people didn't want to give up the idea. And I agreed that, now that we had the capability, we would never solve the problem by just looking at Mars from the Earth. This was a classical problem, part of Western culture, the idea of life on Mars
has been around for three hundred years. And here was the first time we had the ability to test it.

“Mariner 9 found an objective argument for flying to Mars, because [it] saw that Mars once had water on it. There are dry streambeds, obviously cut by water. All the geologists agree that they're water cut; there was water on Mars at one time. And you could say that, if there was water on Mars, then there may have been an origin of life, and that life may still be surviving. Now Mariner 9 was an orbiter…and up to that point, up to the time Mariner 9 took its photographs, I would have said the a priori probability of life on Mars was close to zero. It would have really been an irrational act to fly to Mars before 1971 to look for life.”

But, as with his life-science experiments onboard Viking, studies on Earth would prove a valuable precursor to experiments on Mars. And few places on Earth were as close to the Martian environs as Antarctica.

“Another important thing I initiated at JPL [were] studies in the Antarctic. I never went to the Antarctic myself, but there was a microbiologist at JPL named Roy Cameron who studied microbial life of the world's deserts—he was traveling all the time. Just before I went up to JPL, I read a report of biological work that had been done in the Antarctic during the International Geophysical Year, around ’58…. [T]here are areas called the dry valleys, actually ice-free areas. A team of microbiologists…got in there during the International Geophysical Year and they found that a lot of their soil samples were sterile; they couldn't find any bacteria. These dry areas are as Mars-like as you can find on the Earth. They're very cold and they're very dry. Roy brought back tons of soil…. [These samples were] used for a long time as standards during the testing of the Viking instruments.”

But after all the things Horowitz has experienced and done, studying the most minute organisms on one world and seeking them on another, he still has a broad and revealing global perspective.

“I think that Mars exploration is quite important. If we are the only inhabited planet in the solar system, and there's only one form of life on Earth—I mean, when you look at the composition of living creatures and see that they all have the same genetic system and they all operate on DNA and proteins composed of the same amino acids with the same genetic code…then we're all related. The origin of life may have happened only once, and it happened here and no place else in the solar system. Or if it happened elsewhere, it didn't survive. I think this is a conclusion of really cosmic importance. If people become aware of this, then maybe they'll be less inclined to destroy the planet.”

The exploration of Mars may indeed serve many functions. Let's hope this is one of them.

F
or twenty long years, Mars was left to slumber…six Soviet missions either failed outright or returned only partial results, NASA turned its attentions to the space shuttle and the outer planets, and nothing new from Earth landed on the Red Planet. The frigid surface remained untouched by human endeavor with only two Viking landers and a clutch of failed Russian spacecraft to mark the coming of the human race. Above the ruddy surface, a larger collection of machines remained, silent in their endless orbits.

Then, in September 1992, the United States reentered the fray with Mars Observer. Its goals were ambitious: survey the overall mineralogical and topographical nature of the planet, map the gravitational field, measure the magnetic field, and observe the atmosphere and dust within. It was a robust mission with great hope attached.

Originally intended for an Earth departure via the space shuttle, Mars Observer eventually left Cape Canaveral aboard a Titan III rocket.
¹
Leaving Earth orbit, it headed off into an eleven-month cruise toward Mars. Just short of the first anniversary of the launch, in August 1993, the unthinkable happened: contact was lost with the spacecraft. Commands were sent repeatedly with the hope of reacquiring contact. Controllers waited tensely on the ground for any indication that the spacecraft had merely wandered off course or turned off axis and would recover. But it was not to be, and silence remained the sole result.

Hands were wrung and heads hung low at JPL. Surely after all these years, with the last Mariner failure occurring decades earlier, technology had progressed to the point that spacecraft en route to other planets should succeed, especially those headed to this close neighbor of Earth. But alas, this was not the case. As far as is known, part of the propulsion system failed, disabling the probe. Whatever the case, Mars Observer ceased to observe, and went silent forever.

It was noted in the postfailure investigation that the spacecraft had been converted from an Earth-orbital satellite. Some of the systems (propulsion specifically) might not have been up to the rigors of interplanetary travel. Cost-cutting measures had caught up with optimistic planning, and the entire mission was now a write-off, save for some data acquired along the way. It would not be the last time that misguided frugality bedeviled JPL.

But this was not the end of the road for orbital observation of Mars in the 1990s. In 1996, a Delta rocket roared out of the cape with a 2,200-pound payload, almost exactly the same mass as the ill-fated Mars Observer. It was Mars Global Surveyor (MGS), which would reclaim the mantle of Mars exploration for America. Built by Lockheed Martin, the MGS craft was a simplified version of the Mars Observer. A new high-resolution camera was onboard, along with a suite of other instruments that would replicate much of the capability lost when Mars Observer died.

Once en route, and when the spacecraft deployed its solar panels, there was one mishap discovered: apparently, during the brutal stresses of launch, or upon opening the solar panels, a small damping strut (used to regulate the swinging-open of the solar panel, much like a screen-door closer) snapped, and the stray part had lodged in the fuselage and prevented the panel on one side from fully opening and locking. This was a problem, as the solar panels, once deployed and configured into a V-shaped pattern, were critical to the aerobraking maneuvers once the ship reached Mars. Ground teams worked overtime to come up with a solution.

It took almost a year of drifting through the Great Dark to arrive at Mars, but MGS continued without additional mishap. Perhaps things were looking up. As the craft entered Martian orbit, commands were uploaded to change the course of the probe to enable aerobraking. This relatively new technique would deliberately force the ship into the upper reaches of the Martian atmosphere and slow it down and alter its altitude, over time, from over 33,000 miles to only about 280. MGS would be the first spacecraft to try this risky but elegant technique at Mars.

The reasons for aerobraking were simple. The cost-effective Delta rocket did not have enough thrust to loft a full fuel load for a more traditional trajectory and rocket-braking maneuver to reach Mars. In the case of MGS, the trip involved a long loop around the far side of the sun to get to its target, but it would result in a lower velocity once it arrived. Therefore, less fuel would be needed to slow it into a lopsided orbit, and aerobraking by skimming the atmosphere would trim-up the arrival into a proper orbit to achieve its goals.

Prior to this, JPL personnel had to come up with a solution to the broken strut. The solar panels were actually a part of an aerodynamic design for the craft, interacting with the wispy upper atmosphere to help slow and lower its orbit. With one of these panels hung up, not only could the spacecraft be unstable (even in the tenuous upper atmosphere), but the pressure of ongoing aerobraking maneuvers could further damage the panel mount, and maybe destroy the entire probe. The solution? Rotate the panel 180 degrees to present the solar-power-generating side to the winds of the upper atmosphere. Not only would this avoid further damage, but it might also act to help the panel latch into a locked position.

Aerobraking is a slow process, and it took nearly one and a half years to accomplish. The Martian atmosphere is thin at the surface, and exponentially more so at high altitude. But to avoid damage to the craft, only the fringes of the atmosphere must be
allowed to drag on the ship.
Caution
was the watchword for this portion of the journey, as aerobraking was critical to success, and without careful completion of the maneuver, the mission would fail. This would be a kinder, gentler aerobraking approach than originally specified, in hopes of suspending further damage to the delicate craft. It worked.

Patience is a virtue often rewarded in space exploration.

Finally, in March 1999, the desired orbit of about 280 miles was reached. At this altitude, MGS would circle the planet every two hours. The orbit was polar in orientation, that is, moving from north to south instead of along the equator. While more challenging to accomplish, the scientific yield would be much higher, as with this orbital path, every part of the planet would repeatedly pass underneath the cameras and other instruments.

Soon the mapping runs began, with high-resolution images flowing in hourly. The scientists were ecstatic. The onboard cameras, a new high-water mark in camera design for a Martian probe, showed objects as small as eighteen inches across. At centers around the country, working in tandem with JPL, breathless researchers eyed each new photo pass with glee. While the images from the Viking orbiters had been striking, these were exponentially more detailed. Additionally, due to the polar orbit, MGS eventually covered the entire surface of the planet in approximately the same lighting conditions on each pass. The results were stunning.

While it had been clear that wind, sand, and water (in some form) were at work on the Martian surface since Mariner 9, these new pictures allowed planetary geologists to refine their theories about weathering, hydrology, and atmospherics on Mars.

Early interpretations of the imagery showed more detail of the landforms that had so baffled scientists, confirming that these were in fact wind- and water-sculpted formations. This was exciting news, for it indicated not only an active weather system, but also evidence of vast amounts of water somewhere in Mars's past sufficient to carve out huge masses of soil and rock. Until
then, orbital data had not formed a clear picture of what might have been at work earlier in the history of the planet. But here it was—in stunning detail—evidence of huge masses of water sometime long ago. And where there was water, there could have been—and might still be—life.

Other instruments onboard included a sophisticated laser altimeter, allowing MGS to measure the elevations of Martian topography accurate to
one foot.
This allowed planetary scientists to not only map the rocks and sand of Mars, but also re-measure areas of interest across many years, sometimes catching differences in height that indicated erosion and soil movement.

A thermal spectrometer allowed researchers to see the planet in infrared, which demonstrated yet more evidence of large masses of water in the past by revealing topographic evidence of ancient hydrothermal activity and water flow. It further indicated large deposits of hematite, which often originates in large bodies of standing water.
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A magnetometer measured Mars's weak magnetic field, which, unlike Earth and Mercury, does not originate from a heavy, central, iron-rich core. Rather, the magnetic masses are concentrated in various areas around Mars, indicating massive volcanic activity early in the planet's history. Further data showed a deeply layered crust on Mars, reaching to a depth of over six miles. This indicated the likelihood of a smaller molten core than Earth's.

Although the two hemispheres of the planet appear to be very different—the top half is smoother and lower in elevation, while the bottom half is much more intensely cratered—it was now apparent that there were plenty of craters in the northern areas as well, but many had been buried. But buried how? Making things more complex, the vast majority of the surface was underlain by volcanic rock. So it was, at one time, a highly active planet in geological terms. This confirmed widespread volcanism, not just in the region of the giant volcanoes evident to the north.

Also, while not scientifically significant in the traditional
sense, MGS photographed the Cydonia area of Mars, which a Viking orbiter had imaged in 1978. At that time, the first pass by Viking showed an area that vaguely resembled a human face. While the planetary science community was unmoved, it created a popular sensation, championed by some less-than-stellar pseudoscientific personalities. And despite the fact that later Viking images of the area seemed far less facelike, a myth was born. Some wanted desperately to believe that it was an artificially created structure. Then, in 2001, MGS imaged the area again. It was a spectacular shot, but not appealing to the true believers. The region, while still eerie in appearance, was clearly the home of a large erosional feature—a result of weathering, not intelligent design. It no longer strongly resembled a face; any likeness was vague at best.
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Finally, in one of its last acts of great scientific return, MGS produced images that seemed to indicate recent water activity. In December 2006, gullies with fresh sedimentation were spotted inside two craters, Terra Sirenum and Centauri Montes, and this would have to have been caused by water flowing within the last few years, arguably sometime between 1999 and 2001. This was staggering news, as it had been generally thought that whatever water had been on Mars was long gone, or permanently frozen deep underneath the crust. Some mechanism must have heated and released the water required to accomplish this. Whatever the case, this was a major discovery.

As with most of the spacecraft launched from JPL that reach their destination successfully, MGS was not yet finished at the end of its primary mission. The machine was well designed, well built, and well handled, and had much more to offer. The mission was extended three times past the planned 2001 end date, and MGS returned data until November 2006. Then, it abruptly stopped speaking to ground control.

This failure occurred after a series of commands had been sent to the spacecraft to reorient its solar panels. The onboard computer signaled a series of alarms, including some related to its orientation, but then reported that it had stabilized. That was the last message sent earthward by the probe. Various attempts were made to reacquire contact with the spacecraft, and three days after it went silent, a faint signal was received indicating that MGS had gone into “safe mode,” a computer condition that occurs when the situation aboard the probe is not as expected. Nonessential systems had been shut down and the craft was awaiting additional commands.

JPL does not give up on its interplanetary emissaries easily. Controllers even pulled a later arrival to Martian orbit, the Mars Reconnaissance Orbiter, into the rescue effort, attempting to snap a picture of MGS to observe what condition and orientation it might be in, but this was not successful. MGS's younger sibling would not be of aid.