by Rod Pyle
Soon the lander unhooked from the parachute, now relying only on its tiny landing rockets to control the final descent. At three hundred feet up, low-level radar kicked in to give a last set of readings. At sixty feet, the computer worked to cancel any horizontal motion and the lander settled into a strictly downward mode. It would now land directly below, no matter what. So said the simple instructions burnt into its primitive memory, saved in tiny magnetic cores that lived at the intersection of minute, hair-thin wires. While brutishly dumb by today's standards (your toaster probably holds more data), it was an elegant and almost bombproof method of storing data.
Slowly, Viking descended the final few feet. The rockets would not shut off until the lander made ground contact. But what lay below? The Viking lander had a scant 8.5 inches of ground clearance; any rock larger than that would likely end the mission. Falling in the weak gravity at a leisurely 6 mph, about the speed a person can walk, Viking 1 settled onto Chryse Planitia, Greek for “Golden Plain,” a large and relatively flat expanse not far from the Tharsis volcanic region.
Touchdown. Silence returned to Mars. The Viking 1 lander was down, alive and well, after a 440,000,000-mile journey.
The date was July 20, 1976, the seventh anniversary of the landing of Apollo 11 on the moon. It was the first US soft landing on another planet (a moon is a satellite), and the first probe to function for more than a minute on another planetary body (an earlier Soviet probe had landed, but failed upon touchdown).1 In fact, it would perform well beyond its builders' wildest expectations.
As the lander began surface operations, the Viking orbiter continued overhead, entering a new phase of its own science program. Armed with high-resolution cameras, it continued its observations while also acting as a relay station between the lander below and Earth, a blue star barely visible over the horizon.
Lander 1 went through a deliberate cycle of making sure that the descent engines and associated systems were shut down. It would not do to drip anything caustic or polluting onto the ground below. Hydrazine, the craft's volatile and corrosive fuel, would not be friendly to any microorganisms lurking about and would be a terrible way of saying hello. In fact, not so much as a microbe of Earth biota had been knowingly allowed to fester on Viking either; it had been baked, purged, and sterilized better than any surgeon's tool before launch. Nothing could be allowed to pollute the virgin Martian soil.2 As the engines were “safed,” the computer queried the navigation system, or inertial guidance unit. This simple system, while no longer needed for steering the craft, would help to supply altitude and directional information, so it was run for another five minutes. This information was critical to aiming the radio dish toward Earth, so the more accurate the data, the better.
At the same time, the first postcard to home was being assembled. The Viking landers used a new type of imaging camera. Previous space probes had used state-of-the-art TV cameras, but at the time, the images were not up to what the designers had yearned for. For Viking, the camera stared upward into a mirror that swung vertically, “nodding” up and down. Between each nod the mirror would rotate a small amount. In this way, a series of strips were assembled over time, and these resulted in what was, for the day, a very high-resolution image. Two of these ingenious devices were mounted on each lander, allowing three-dimensional imaging, and the first job of the day was to send an image home.
But this first snapshot of another planet was not to be a splendid panoramic of the landing area; rather, it was a somewhat mundane image of the nearest footpad. This would accomplish multiple goals instantaneously: the safety (or lack thereof) of the landing site would be demonstrated by the placement of the footpad. The amount of sinking into the sandy soil (properly called regolith, as the word soil implies life within) would be shown, and this, along with other measurements such as the amount of slowing at contact and the designed-in collapsing of the lander's legs upon touchdown would supply information about the compactibility of the ground. Remember, nothing is wasted in space exploration.
Back on Earth, strips of the first picture from Mars began to come in. It was innocuous enough: a shot of footpad 3. If the probe had failed then and there, a lot of folks would have been very upset to have nothing more to show for the billion-dollar effort. But this shot was needed to ensure that the craft was stable. Cheers rang out at JPL and Caltech as the proof of a successful landing were made visible. But from Mars, the lander could not hear, nor would it have cared. It merely carried on in its eighteen kilobytes of programmed duties with dogged and ruthless determination.
Next on the lander's to-do list were the pyrotechnic events, known to most of us as explosions. In spaceflight, whether manned or unmanned, small explosives had long had a leading role. Then as now, they were used to separate the stages of rockets as they ascended away from Earth. They released spacecraft once in orbit. They opened and closed valves. And, in Viking's case, they were critical to beginning Mars-based activities. These are, by their nature, one-shot operations—as in, they work or they don't. Their duties included releasing safeties for the life-science experiments and opening the meteorology boom—an arm with instruments to measure wind speed, temperature, and the like. These performed without a hitch.
Now a second photo was taken, and this was the money shot: the first picture of the horizon of Chryse Planitia. As the lander went about its business, breath was again held in mission control. What would we see? What did the surface of Mars look like at ground level? Remember that these were the days of rotary telephones, bias-ply tires, and such state-of-the-art things as The Eagles: Greatest Hits via vinyl records. An image from the surface of Mars was heady stuff. And with the Viking orbiter disappearing over the horizon in about twelve minutes, and with it, the best link to home, this had to be done now.
Once again, Viking 1 did not disappoint. The first image, black and white but glorious nonetheless, slowly assembled, again, a strip at a time. The tension broke slightly as the first strip came in, but like a good mystery novel, Mars was only revealed a small bit at a time. The results were well worth the wait. After years of preparation, a billion dollars, and a journey of many times the 119 million miles then separating Earth from Mars, the first landscape was in. The data was still coming back long after the orbiter was out of touch, given the long transmission travel time across the vast darkness, and the lander went into a base-operation mode while out of communication.
But the picture…oh, that second picture. It lacked color and was obscured on the bottom by various parts of the spacecraft. But there it was, in all its monochromatic glory: the horizon of Mars. Low, arid hills were off in the distance, and between the lander and those hills was an expanse of sharp, jagged rocks. Hundreds of them. And off to the right, dominating the horizon there, was the bright glow of the sun, unseen and above the frame. It was a dry, cloudless spectacle. For someone seeking the serenity of an English tea garden, or the Mars of Percival Lowell, it would not do. But for any human pining for a glimpse of another world, a world we could relate to, another planet to which we might one day travel, it was nirvana.
Viking 1 was, however, oblivious to such human emotion. The outbursts and cheers from Earth remained unheard. It had a primary mission of just sixty days on the surface, with an extended mission target of 120. At that point, Mars would pass behind the sun and communication would be lost for weeks. And while controllers on Earth planned to “safe” the lander during this time, their confidence in reawakening the machine after this period was limited. But true to what would become JPL's legacy of performing near miracles with distant machines, the first lander operated successfully for well over six years. And the tale of its ultimate demise is not one of equipment failure, but of human error.
With Viking's successful landing, there was now time—well over two months in the primary mission alone—to perform the tasks it was designed to do. The instructions came up from Earth in carefully coded batches, to be processed and executed in sequence. With mechanical exactitu
de, Viking 1 began its primary labors—taking color images of the surrounding surface, digging scoops of soil and dumping them carefully into small funnels that led to an onboard laboratory, and fulfilling its primary objective: the search for life on Mars.
Just under two months later, on September 3, 1976, the Viking 2 lander settled gently onto Utopia Planitia, 4,200 miles away to the northeast. Humanity now had two outposts on Mars, and the exploration of the red planet began in earnest. Overhead, the Viking orbiters continued to chip away at their intense workload, snapping pictures and sending reams of data earthward. What they imaged and reported would change our understanding of Mars overnight: the Martian Renaissance had begun.
Exploring Mars is a bit like doing brain surgery through a mile-long soda straw. At an average distance of fifty million miles from Earth, with a one-way radio message time of twelve to twenty minutes, roving the dry, treacherous surface requires the utmost in planning and careful execution. One false move can end a mission in seconds, and there are rarely many options to correct a mistake. That is why the people who dare seek the truth about Mars are so remarkable. This is the story of human striving, from early times through tomorrow, to discover what makes Mars tick.
Orbiting in the dark cold of space at an average of about 140 million miles from the sun, or about half again as far as Earth, Mars is the fourth planet in the solar system. It is also the last stop for the rocky, or terrestrial, worlds before the gas giants Jupiter and Saturn and the icy balls of Uranus and Neptune. It is separated from these giant worlds by the asteroid belt, a planet which failed to form from the large disk of material that still orbits the sun beyond Mars.
The air on Mars is thin and cold; the highest temperatures hover at about 60°F, and can plummet to -180°F at the poles. Its day lasts about 24 hours, 37 minutes, and its axial tilt matches Earth's at 24 degrees. Its year lasts 686 Earth days. Mars is about half the diameter of Earth, less than a quarter its size, and has only 11 percent of Earth's mass and 38 percent of its gravity. Despite this, it has almost the same dry surface area, due to a lack of seas and oceans; in fact, bodies of liquid water do not exist on its surface. It is a bone-dry, ultracold place with only about 1 percent of Earth's atmosphere.
Why then, one might ponder, are we so fascinated with this seemingly inconsequential world? Because Mars is a planet of dreams. Always, it has inspired feelings in humanity as no other planet in our solar system. Early on, it was the reddish hue, resembling the color of aging blood, that attracted the naked eye. Later, in wavering telescopic images transmitted across the tens of millions of miles from its surface, it was the odd markings and, still later, imagined lines crossing its surface that inspired. One could imagine life there. One could imagine…empires.
And why not? The planet is not that far from Earth, and must then be not so unlike our own world, or so the thinking went. If Venus, one step closer to the molten sun, might be covered with tropical oceans and riotous growths of green, steaming jungles under its impenetrable cloud cover, why couldn't Mars, still within the so-called Goldilocks Zone, harbor an older, wiser, more advanced civilization?1
But of course, those dreams vanished along the way. Venus turned out to be an unbelievably hot hellhole with over nine hundred pounds per square inch of pressure crushing its deadly surface. But the real Mars, as we know it today, is not so much less interesting than the one of previous generations. The empires of Edgar Rice Burroughs's green men and eight-legged Thoats (dinosaurlike steeds) might be gone, but in its place is an old, highly weathered, and geologically fascinating place with signs of vast and ancient floods of liquid water, and more recent indications of smaller flows.
The planet seems in many ways to be an older version of our own. But it is an Earth with planetary evolution gone awry. Once rich with oceans and cloud cover, it is too small to any longer harbor liquid water on its surface for more than a few moments. Its thin atmosphere is almost entirely carbon dioxide, with bits of nitrogen, argon, and oxygen existing in wisps. Most of the life-sustaining oxygen that we prize so highly has been long spent, slowly turning the iron in the soil a ruddy, oxidized red. And that thin atmosphere has also allowed for billions of rocks, most of which would burn up or explode in Earth's denser atmosphere, to slam into Mars's surface with impunity. Many millions of these were large enough to leave wounds on the planet, and some created vast new surface features.
Another seeming indicator of a dead world is Mars's lack of a meaningful magnetic field. This is probably due to a largely inert core, or a cooling one. Whatever the case, there is not the same molten, metallic dynamo that creates Earth's robust lines of magnetic force, and what magnetism Mars does possess is lumpy and erratic. The gravitational field is also unlike Earth's, with mascons (mass concentrations), not unlike those within Earth's moon.2 Whatever the case, Mars has, proportionally, a much thicker crust and a smaller, less active molten core than our planet.
Still, Mars has possessed life, though not the kind we seem to wish upon it. It was geologically alive, with vast lava flows and wind and water erosion working their healing magic upon its tortured and pockmarked surface. While much of the southern half of the planet still bears the scars of bombardment, the northern half is largely covered with younger lava flows that filled in the offending craters. And the source of much of this once-molten rock can be clearly seen with even low-resolution cameras from the myriad probes that have flown past the planet, in the form of the Tharsis Bulge and its huge volcanoes. This region is so remarkably swollen that it noticeably deforms the otherwise spherical planet. And it is home to some of the most impressive mountainous real estate in the solar system.
What follows is a brief primer of Martian geography. Entire sets of texts are available on the subject; what is presented here is merely the briefest of samplings. The intention is to present a general idea of the important regions of the planet in both historical and scientific terms.
First among the huge volcanoes identified within the Tharsis region is Olympus Mons, the largest known mountain anywhere, which flanks the bulge. Three times the height of Mount Everest, the now-extinct volcano soars fourteen miles into the thin Martian air. It is a shield volcano, resembling those that comprise the islands of Hawaii, with a base width of almost four hundred miles. The area it rests upon is roughly the size of Arizona. It is also the youngest of the major volcanic structures on Mars.
Directly atop the bulge and spanning its crest diagonally are three older volcanoes, all shield volcanoes, Arsia Mons, Pavonis Mons, and Ascraeus Mons. While subordinate in size to their larger sibling, these lava factories contributed greatly to the basaltic flows that inundated much of the surrounding area. Overall, the Tharsis region is the size of a terrestrial continent.
The formation of this region was not without its side effects, and a gigantic wound in the planet can be found nearby, stretching east from the Tharsis area and continuing along the Martian equator for about a quarter of the planet's circumference. This gigantic gash in Mars's hide is called Valles Marineris. In keeping with the Texas-style “bigger is better” nature of Martian topography, it is the largest valley in the solar system. Our own Grand Canyon would be scarcely noticeable alongside it. Almost 2,500 miles long, it was formed when the Tharsis region rose out of the planet, and the nearby crust could not take the stresses of this enormous violation. So it cracked and slumped, resulting in the huge channel. It averages 125 miles in width and is as much as 4.5 miles deep. It is outclassed only by the underwater Mid-Atlantic Ridge on Earth.
To the north rests Alba Mons, also known as Alba Patera, the oddest of the volcanoes and unlike anything else on Mars (or Earth, for that matter). It has the gentlest slope of any Martian volcano, with an inclination of just one-half a degree, or about a tenth of that of Olympus Mons. Its volcanic outflow forms an ellipse almost 2,000 miles across and 1,200 miles north to south, making it (here, again, the Texas-style attributes) among the largest known magma generators in the solar system. There are
many theories seeking to explain its productivity, including the existence of highly fluid magma that flowed freely and fluidly out of the caldera and across the surface of Mars. On Earth, the total outflow of the volcano would have covered most of twelve states if centered in Colorado. It's a big beast.
Other volcanic regions include an area thousands of miles west of Tharsis called Elysium. Here we find three main volcanoes: Elysium Mons, Hecates Tholus, and Albor Tholis. Finally, down toward the equator is the region of Syrtis Major Planum with its own volcano of the same name. About 750 miles wide, but only one mile in elevation, this vast, low-lying monster produced lavas that seem to be different than that from the Tharsis volcanoes; it is more complex and differentiated in geological terms and is thought to have formed in the vast three-mile-deep magma chamber below when heavier elements settled out, leaving the lighter lavas to spew forth.
In any case, by the time Mariner 9 had begun sending back images of the Tharsis volcanic complex, any thoughts that Mars had been dull or uninteresting in its youth were banished. While the planet may have slowed down in its old age, in earlier eras it was a geologically active toddler, with regular volcanic tantrums to match.
