by Rod Pyle
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.
For 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 ma
neuvers 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.2
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.3
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.
In the final analysis, it appears that a programming error—a human failing—caused the ship to turn into an improper orientation with regard to the sun, overheating the onboard batteries and causing them to fail. With no power (as the solar panels were not correctly aimed at the sun) and dying batteries, the craft had little time to reacquire a signal with JPL. And while its programming likely resulted in its searching for a proper orientation to talk to its masters, this software did not include a way to keep itself safe from the rays of the sun, destructively hot even this far away.4
While the craft died what was ultimately deemed an unnecessary death, the mission was a vast success. MGS operated four times beyond its primary mission, and for almost ten years, longer than any other Mars orbiter. It provided evidence of huge masses of flowing water on Mars (heretofore thought unlikely, despite the visual evidence), and found deposits of minerals that further indicated massive water flows in the past, helping to select future Mars rover landing sites.
The oversights that resulted in its demise also triggered a thorough review of the safety features loaded onboard future spacecraft, and this is how places such as JPL refine their approach to space exploration. While all contingencies are considered as thoroughly as possible in advance, it is by failures that we learn to avoid such future debacles. And this paved the way for even more successes ahead.
