The Sirens of Mars

by Sarah Stewart Johnson

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  THE INTEREST IN the wave of darkening reflected a subtle shift that had played out in Mars science in the early twentieth century: from Mars as home to a civilized world to Mars as home to a vegetated world. William Pickering, the same man who had led Lowell west to Arizona, had played a key role in developing the idea of a botanical Mars. Pickering was an astronomer and a naturalist. He was an intrepid hiker. At twenty years old, he’d climbed Half Dome in Yosemite, and by twenty-four, he’d created the first recreational guide to the White Mountains in New Hampshire. He included descriptions of how to reach a summit in the absence of a trail and advice about the use of tar soap and pennyroyal for mosquitoes, milk for sunburn, and washleather for blisters. He spent hours gazing at dramatic escarpments. “It is then, and only then,” he once wrote, “when high above the tree-line, with one or perhaps two companions, that the grandeur and loneliness of the great peaks really break on [a person]; then for the first time does he begin to understand…”

  Pickering loved gazing into the distance, and he loved gazing at Mars. He preferred wild places for astronomical observing, where the viewing conditions were exceptional, he maintained. There was simply less water vapor to wobble the air, and fewer clouds and storms at altitude on mountain peaks. With the help of his older brother, the head of the Harvard Observatory, he led several efforts to establish remote astronomical observatories, including Lowell’s in Arizona. For a time, he used this belief in the superiority of remote locations to defend the existence of the lines that Lowell believed were canals. Like Thomas Henry Huxley, who protected the theory of evolution so vigorously that he came to be known as “Darwin’s Bulldog,” Pickering vehemently argued that the astronomers in northern Europe and the eastern United States who had not experienced a place like Flagstaff had no right to opine about the reality of surface markings on other planets, as their observatories simply didn’t allow for “good seeing.” They might as well express their views on electrodynamics or physiology, he maintained, or other areas they knew nothing about.

  Pickering, however, never fully bought into Lowell’s explanation. He didn’t deny the possibility that an intelligent civilization might exist on Mars, but he did harbor doubts that the canals were foolproof evidence of one. His observations from his outpost in Peru had nursed his hesitation, and he came up with many alternative theories.

  For instance, in 1905, while he was exploring the volcanoes of Hawaii as possible analogs for the moon, he happened to notice a series of cracks in the desert extending to the south of Kilauea. Based on those volcanic cracks, he began to suspect that the Martian canals weren’t waterways crossing dark patches of vegetation; rather, the “canals” were themselves vegetation. Waterways should have glinted in the sunlight, after all. But if steam was emerging from naturally formed cracks, that could in turn nourish plant life like trees, low bushes, and ferns. He knew that this idea wasn’t entirely satisfactory either, as it postulated lots of volcanic activity on the surface of what everyone knew to be a small, cold planet. But he kept playing with the data, turning the evidence over, seeking out clearer observations and better theories, never convinced that the lines on Mars were quite what they appeared to be.

  Then, two years later, in the Azores, he found himself gazing at a hill from a distance. Once densely wooded, it had been deforested in geometric patterns to make pastures for cattle. Suddenly, another theory for the linear features came to him: Perhaps the lines were a vestige of a plant species in decline? “Imagine that the whole surface of the planet was originally covered with some form of bush or tree, which in the northern and equatorial regions has now been largely destroyed,” he wrote. “Its continued presence in the southern regions would account for the so-called seas, while narrow, more or less continuous, strips of it would account for the canals.”

  In 1911, Pickering set sail for the British West Indies, to a high plateau in the central mountains of Jamaica, with a pocketful of funds from the Harvard Observatory, determined to establish a small viewing station there. He leased a one-story plantation house that would be his base. There were no lights or running water or telephone. On a large patio once used to dry coffee beans, Pickering set up his twenty-eight-centimeter Clark refractor. In order to appease his older brother, who was working hard on a stellar map of the sky, he’d occasionally observe a double star, even though he “didn’t care a whoop about the stars.” It was known that many of them had burned out long ago, even though their light still traveled toward the Earth, and he couldn’t be bothered with creating a catalog of useless suns. “The enormous size of our stellar system is of no consequence to us,” he once wrote. “If it only contained ten thousand stars instead of a thousand million we might perhaps be just as contented.”

  It was beneath the telescope on that patio that Pickering developed his final theory to account for the canals: Again, it was vegetation-based. Mars’s atmospheric circulation, which he conjectured to follow regular patterns, resulted in certain parts of the ground being moistened again and again by thunderstorms. The straight, narrow bands beneath those regular squalls had then become marshes teeming with life in an otherwise-silent landscape. “Had it not been settled by the Europeans,” he wrote, “the United States would still be a wilderness. How much less should we hasten to accord civilization to a planet of which we know little…” Instead of being irrigation ditches or pseudo-canals, he concluded, the patterns, however straight they appeared, were accidental.

  By the time he had devised this theory, however, it was 1914, and terrestrial catastrophe loomed in the form of the impending World War. From his secluded perch in Jamaica, Pickering seemed to take refuge in a nearly obsessive series of Mars observations, each transmitted in a monthly report. To him, Mars was a pristine wilderness. Without civilization, there could be no war, no conflict. He was pushing sixty, too old to be called up, but still with a youthful toughness about him, his boyish eyes staring out from a face creased by sun and wind. His beard, even when trimmed, had an unruly spray of hair at the chin. He refused to own an automobile, so when the time came to cable his reports, he trotted into the nearest town on one of his two horses, Jupiter and Saturn. He fancied himself less a scientist than an emissary, particularly to astronomers in the northeastern United States, a class of people “not fortunate enough to reside in those portions of the world where the seeing is habitually good.” His reports were full of maps, data tables, and scatterplots, but, eager to defy convention, he didn’t send them to scientific journals. He instead sent them to an American magazine called Popular Astronomy.

  These bulletins represented the first time that the world received regular news reports about another planet. He kept it up for years, spending nights beside the plantation house-turned-observatory, recording his impressions of Mars into leather-bound books in skittish, swooping cursive. He made hundreds of pencil sketches, capturing the changes in Eden, Elysium, Arcadia, Chryse, and Utopia. They were joined by dozens of paintings, delicately colorcast in carmine and shades of sienna. All the while, he knew that the astronomical community was moving toward photographic research, using techniques Pickering himself had helped to pioneer. Yet he was undeterred, becoming increasingly convinced that the “human eye must reign supreme.” It was not long before he abandoned astrophotography almost entirely in favor of basic visual observations of planetary surfaces.

  In his reports, he tried his best to stick to what he saw. He laid out a taxonomy of terms. He argued that certain questions were best left “in abeyance,” like the existence of Martians. Nevertheless, his vision of the landscape permeated everything he wrote. He talked of growing and receding storms. He reported on the coastlines of blue-tinted bays, the greening of the southern maria, and the wild, heavy rain falling in dark, uniform sheets. Sometimes, gargantuan floods surged through the north like the spring torrents of Siberia. At other times, belts of high-rising cumulus clouds swept the sky
, not unlike those he’d seen above western Bolivia. He reported when the south polar cap seemed stippled with hoarfrost and when icefields appeared in the torrid zone. He announced when Mars was “snowed under” as far south as southern Labrador on Earth. In so doing, Pickering brought the world a new vision of Mars, an alien marvel that was no less glorious for its lack of a civilization. It was an expansive, unexplored landscape, every bit Earth’s equal.

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  PICKERING’S VISION OF a vegetated Mars resurfaced before the launch of Mariner 9, though not exactly as his missives portrayed it. No longer was Mars imagined as having teeming marshes or a surface that was like a thickset stretch of the Amazon basin, where during the rainy season hundreds of kilometers were flooded to the depth of several meters. No longer was it understood to have a dense atmosphere, welling with storms and full of moisture and heat. Temperature measurements of Mars with vacuum thermocouples—circuits of wispy wires of different metals soldered end to end—suggested that conditions were cold, but not that cold: the thermocouples registered signs of warmth in Mars’s dark areas, measurements that could be explained by the growth of simple vegetation like moss and lichen, not unlike the Siberian tundra.

  Despite his deep affection for the “grandeur and loneliness of the great peaks,” Pickering had believed that the surface of Mars was devoid of high mountains, a commonly held belief that also persisted right up until the arrival of Mariner 9 in 1971. After all, Mars was far smaller than Earth. How could such a tiny interior generate enough heat to sustain vigorous volcanism and plate tectonics, the forces that build mountains? In fact, his final vegetation theory depended critically on the premise of a flat surface; without it, the atmospheric circulation patterns fell away, along with the squalls that watered vegetation, lush and wild.

  For two months after arriving at Mars, Mariner 9 continued to patiently circle the planet as the dust storm raged on. In early January, after weeks of waiting, observations showed that the dust finally appeared to be receding. Recognizable features were beginning to peek through the red haze. And when at last Mariner 9 began its imaging, the surface revealed itself to be anything but level. The first thing to emerge from the dust pall was a sort of fuzzy spot. The imaging team, beside themselves with excitement, began poring over the classical maps to identify it. It seemed to align with the approximate location of Nix Olympica.

  In the days that followed, three more spots slowly appeared, all in a line, which the team dubbed “North Spot,” “Middle Spot,” and “South Spot.” A press conference was scheduled. In the midst of it, surprising everyone, the head of the imaging team blurted out that the spots must be the summits of wildly tall volcanoes. They simply had to be high areas, towering above the dust. He divulged that he thought he’d even seen collapsed craters, characteristic of cauldron-like volcanic calderas that form when a magma chamber empties. NASA had flown by Mars three times and hadn’t seen a single volcano. In fact, Mariners 4, 6, and 7 hadn’t spotted any topography at all on the planet’s surface. In the parts of the planet they’d imaged, there wasn’t a single significant shadow, not a single contour on the horizon. And if the spots were in fact mountainous volcanoes, they were far larger than any volcano on Earth.

  The head of the imaging team was right: The three spots on the crest of Tharsis Rise were volcanoes with calderas. They would become known as the Tharsis Montes: Ascraeus Mons, Pavonis Mons, and Arsia Mons. Nearby Nix Olympica was reclassified as Olympus Mons, one of the largest mountains in the solar system. The existence of volcanoes—clearly the mark of a once-hot interior—was as thrilling as it was unexpected. It meant Mars must have had large inventories of gases bubbling out of magma, the same gases that originally filled our atmosphere and condensed to fill our oceans.

  The volcanoes weren’t the only enormous features on Mars. There were also gargantuan canyons, revealed slowly as the images rolled in. “We saw them coming,” recalled engineer Norm Haynes. Seeing the pictures as they arrived “was like pulling back a curtain, little by little, day by day.” Eventually, when the orbital swaths were laid down side by side, it became clear that the planet’s side was split like the Great Rift Valley. A nearly 4,000-kilometer gash ripped through the equator, large enough to engulf the Grand Canyon again and again, stretching around a fifth of Mars’s circumference. It would become known as Valles Marineris, the Valley of Mariner. Far from being a cratered, empty expanse, Mars was a place of enormous variation. It was just by chance that the earlier flybys had missed, well, everything.

  With the settling of the dust, however, the idea of great tracts of vegetation on Mars evaporated. Mars had a wildly dynamic surface, but there was no evidence of hardy (if water-starved) primitive plants. It was true that only a few weeks sufficed to change the landscape completely, as the early studies had noted, but it wasn’t the blossoming of spring vegetation. The Mariner team soon realized it was just the simple physics of seasonal warming on the Martian surface. As the planet tilted toward the sun, the sun heated the surface and the dust was lifted and shifted, exposing the bare underlying rocks. At great distance, this gave the impression of a bloom. The wave of darkening was just a systematic redistribution of the massive blanket of dust upon the surface, and just like that, the concept of vegetated Mars fell away, just as the idea of a civilized Mars had slipped through our fingers.

  Alongside this disappointment, however, came something else, something stunning: unmistakable evidence of riverbeds. There were no linear features on Mars, no geometric lines on the surface, but the pictures clearly revealed branching forks and catastrophic outflow channels.

  It was almost impossible to believe, and at first, few on the science team did. For years, evidence had been building for a dry Mars. Many on the team wondered if the apparent riverbeds could have been cut by lava, but the riverbeds weren’t found only in volcanic terrain. They seemed to have distinctive meandering patterns and sandbars, the kind of features any hydrologist would instantly recognize.

  But how could there be riverbeds? There was virtually no water vapor in the atmosphere. The low temperature and low pressure meant that any water that did accumulate on Mars would either freeze or evaporate rapidly. The surface pressure on Mars, six millibars, is just past the triple point for water, the ethereal combination of conditions where it coexists as a solid, liquid, and vapor. I remember seeing it with my own eyes the summer I ran the experiments in the Mars Surface Wind Tunnel at NASA Ames.

  The first time I drew a vacuum, I purposely—just for fun, at the suggestion of a graduate student—left a small glass of water sitting on the lip inside the viewing window from the control room. As the air disappeared from the colossal chamber, the water in the glass slowly began to boil, then boil violently. It started splashing over the edge of the glass, splattering on the window. Then suddenly the absurd: A shard of ice appeared, right in the middle of the boiling water, bouncing around the glass like a phantom.

  I understood what was happening. I’d read about the heat of vaporization in my textbooks, how a substance will cool as it evaporates, even as it boils into a near vacuum. But no amount of physics could remove the spell I was under. I gingerly touched the control boards. I looked at the graduate student, then at the young lab director, then back at the boiling ice. Is this what the Mariner 9 scientists experienced—this profound disorientation?

  There they were, looking at images that upended everything they knew, deep in a wilderness of the unexpected. What other physical laws would break, what other mysteries of the universe would burst forth from those pictures? The idea of rivers on Mars was shocking on two counts—it seemed to require a miracle to get enough water on the surface, and then it required another miracle to keep it there long enough to erode a riverbed. Even a knee-deep rivulet in the deepest reaches of the Martian surface, the places with the highest overriding surface pressure, might vanish between dawn and dusk at prevailing surface pres
sures.

  But if the features weren’t carved by lava or another viscous fluid, it meant that Mars must have been a dramatically different place earlier in its history. And to understand that would require much more than understanding the planet as it was now. It would require piecing together a complex and dynamic account of its journey through time. It was no longer the wave of darkening we needed to explain but the staggering mystery of features that looked for all the world like riverbeds. And it meant entertaining the possibility that Schiaparelli had been right, at least in part: Perhaps natural waterways had coursed across the surface of Mars. Perhaps this blighted, empty, cratered planet had once harbored life.

  IN THE EARLY 1980s, not long after I was born, the miniseries Cosmos aired on PBS. My parents tuned in, along with millions of other American households, a public-broadcasting record. For thirteen Sunday evenings in a row, they held my sister and me in their arms on a harvest-gold couch printed with flowers, atop a brown plush rug. They adjusted the antennae of their picture-tube television until the image was clear. It was the first set they ever owned in color, and what a time for color.