The Sirens of Mars

by Sarah Stewart Johnson

  But Pathfinder wasn’t out of the woods yet. The mission wouldn’t be a technological success until the rover powered up, drove down off the lander, and rolled across the surface of Mars. And so it was to the team’s great dismay when the first, dramatic images came back to Earth and showed one of the airbags still billowing in the air. That was a problem: The pyrotechnic devices in the latches of the lander panels were meant to fire and pop free after the spacecraft bounced to a halt, allowing the lander to peel open like a flower and release the vehicle that would actually explore the surface, the Sojourner rover. Winches should have already pulled the airbags back in, clearing a path for the rover to drive down a ramp onto the red ground. Instead, the errant rippling airbag was blocking the rover’s descent.

  In the hours that followed, mission control programmed one of the petals to lift up and flap down again, hoping to clear the finicky airbag from the rover’s path. But during the night, a far more crippling problem arose: Communications between the station and its small companion began breaking up. Sojourner carried nearly the entire scientific payload; the landing station itself was lightly equipped—it had only a camera, three wind socks, and a radio. But the landing station was the rover’s sole link to Earth. On its own, Sojourner’s voice could reach just a few hundred meters.

  The engineers worked the problem, sending commands to switch the radio electronics on and off again periodically for the next twelve hours. Though they never pinpointed the cause of the glitch, the engineers were eventually able to reestablish the radio link, to the point where about 80 percent of the information was coming through. They also cleared the finicky airbag. Even though its first steps were the hardest, Sojourner finally stood up and trundled off the ramp. The rover’s six small wheels, suspended on rocker-bogies, inched into the craggy swales of Ares Vallis.

  Cameras clicking, the rover captured images of boulder-strewn ridges and jagged flood debris, rocks everywhere. The team knew the mission had touched down in a giant outflow channel. The rocks were thought to be from far-off places: from the hummocky hills of Margaritifer Terra, from the tangle of Iani Chaos, from the highlands of Xanthe Terra. They were all out of place, but they might each tell a story.

  Within days, a measurement on “Barnacle Bill”—the first chemical analysis ever made of a rock on Mars—was already starting to reveal a shockingly turbulent past. Barnacle Bill appeared to have been formed from relentless cycles of melting, solidifying, and remelting, meaning that Mars was once characterized by immense heating and internal stress. As the summer progressed, Sojourner trundled on to other nearby rocks—including “Yogi” and “Scooby Doo”—which the mission named after cartoon characters.

  Surprisingly, the pictures coming back showed rounded pebbles strewn about the Martian terrain, and rounded sockets in the rocks too: evidence that they once tumbled through running water. As Sojourner explored, it also discovered sand piled into fluted patterns and, in the distance, cresting into dunes. That meant wind, not just water, had played a powerful role in creating and shaping the planet’s enormous landforms—in forging its bulwarks, molding its attributes. As the rover explored, the scientists working the mission started to realize that they were dealing not just with the landscape spread out before them but also with a highly dynamic history. Apparently, the forces on Mars were once strong enough to tumble the edges from rocks. To pick up the smallest pieces of its world and move them across impossibly large distances.

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  I WATCHED THE Pathfinder mission unfold from a span of old-growth cane forest. I was seventeen years old that summer, and I too was barreling headlong into a new existence. I was going forth, off to begin adulthood, lifted like a piece of spall. I’d spent my entire life in Kentucky, barely ever crossing the state line, but soon I’d start college. I’d already left my hometown: the sweetgums in my backyard, the little brick house where I’d always lived. I’d packed my things into milk crates and driven the hour and a half to Camp Piomingo, where I was spending the summer working as a counselor along the sun-dappled banks of Otter Creek. I had a bunk in an old wooden cabin, and each night, the woods pressed in close. I’d fall asleep to the sounds of katydids and cricket frogs. I was assigned to watch over the counselors-in-training, even though I was new at this myself and just barely older than my charges. I spent my days leading them through caves and on creek walks, shivering as water snakes swept past our limbs. We explored ridges and gullies, repaired trails, and rested in the shade of the rocks down in Doe Valley.

  The day Pathfinder landed was the Fourth of July. I was celebrating our country’s birth, and my own newfound independence, by lighting sparklers at a party on the cabin porch. While I could find Mars in the sky, a steady red drop of light, there hadn’t been a Mars mission in my lifetime. I’d read stories about the rock from Mars the year before, and I’d heard about NASA’s plans for a new wave of robotic missions. It’d been thirty-two summers since Mars exploration had begun, thirty-two summers since my father had read about Mariner 4 on the Courier-Journal’s front page. Now the Courier-Journal headline declared that we were BACK ON MARS, in letters almost as large as the masthead itself.

  In the days that followed, I grabbed the newspaper in morning mess hall. I read about the itinerant rover, named for Sojourner Truth, the former slave who escaped captivity and went on to be a prominent abolitionist, and the rough, rocky floodplain the rover would explore. I read about the engineering systems, about how Sojourner would periodically stop driving and send a “heartbeat” message back to the landing station.

  One of the articles closed with a quote from a professor at Washington University in St. Louis, a Pathfinder scientist working on the very same campus where I would soon be studying. I underlined his name—Ray Arvidson—and carefully tore the article from the page to send to my father, who was certainly following these distant goings-on. I hoped the fact that I would be at a university with a famous planetary scientist would make my parents feel better about the debt they were about to incur to cover the daunting gap between my scholarship and the full cost of attending.

  Once on campus, I made a beeline for Ray’s classroom—that fall, he was teaching a course called Land Dynamics and the Environment. From there it was a short hop to his lab, where he did his pioneering Mars work. Ray was nearly fifty, a Swede who’d grown up in New Jersey. He was humble, soft-spoken, and tremendously respected, having just taken over as the department head of Earth and planetary sciences. He had a short beard that was starting to turn gray, and his eyes crinkled whenever he smiled. He specialized in remote sensing: how to get beyond your immediate environment, how to discern the nature of a place from a distance.

  On his flickering desktop, he showed a group of us how to “see” beyond the visual wavelengths, into the ultraviolet and infrared. Computer techniques stretched and transformed orbital views into a psychedelic swath of colors. He would toggle a few settings on his display, and types of land cover that initially all looked the same would filter in and out, revealing their underlying complexity. We were astounded that by simply adjusting the wavelengths of the light he looked for, he could pinpoint dozens of rocks and minerals that had previously been hidden.

  Ray had grown up shooting off balloon rockets in his backyard. As a graduate student at Brown University, he’d analyzed the Mariner 9 data, then worked on the Viking landers, taking over as the head of the imaging team after the first year of operations. I particularly loved listening to his stories about the Pathfinder mission.

  In one of those conversations, he explained how the simple fact that we’d finally returned to Mars had allowed the team to calculate a crucial variable: the planet’s moment of inertia, which scientists considered the “single most important number about Mars that we didn’t know.” By triangulating Pathfinder’s position with the location of Viking’s landing twenty years earlier, the team could determine the degree to which th
e planet’s spin axis had changed, like the wobble of a spinning top—which helped them to calculate the moment of inertia. With that, the team could discern how mass is distributed in the center of the planet, revealing how Mars formed and how it changed over time. With one landing and a little math, he said, we could peer into the planet’s interior.

  What we learned, Ray explained, was that Mars had to have a dense metallic core. Previously, no one knew whether the planet would have been warm enough to differentiate into layers, but this result indicated high heat flow in the past, which would have warmed the surface, triggering active volcanism. Volcanism, in turn, would have spewed out greenhouse gases, thickening the atmosphere. Higher heat flow also meant that it was conceivable that Mars once had a molten core with an active core dynamo, which would have led to a magnetic field that protected the surface from harmful radiation. And suddenly, Ray said, we understood that Mars might once have been a place with a warm surface, a thicker atmosphere, and a protective magnetic field—the kind of place where life might have taken hold. Like most of my classmates, I neither completely followed nor fully appreciated the science. We were, after all, first-semester freshmen, doing well to find the dining hall. But it did make an impression on me that we could somehow know so much about a place from just knowing where we were—and where we had been.

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  WHEN RAY INVITED me to stay on after my freshman year to work in his research lab with a small stipend from the Missouri Space Grant Consortium, I couldn’t believe my luck. Ray was working with NASA on a new method of mobile exploration. With colleagues from JPL, he was developing a prototype of a planetary payload that could map at far lower altitudes than an orbiter and in the meantime collect atmospheric measurements. This “aerobot” was designed to be piloted through the skies of another planet or moon—Mars, Venus, Titan—like a tiny mechanical hot-air balloon. The idea was to close the gap between the observer and the observed.

  To test the aerobot in the sky, Ray had teamed up with a university alum, an adventurer named Steve Fossett, who was attempting to become the first person to circumnavigate the globe solo in a balloon. It was aviation’s “last great challenge,” and surely its hardest, leaving the pilot completely at the mercy of the winds. He’d chosen to fly in the southern hemisphere, despite the risks of such desolate stretches of ocean, to avoid the political difficulties of crossing China, Iraq, and Libya. Fossett was a fifty-four-year-old commodities broker who’d made his fortune on the Chicago exchange. After he’d tired of finance, he swam the English Channel and climbed most of the world’s tallest mountains. He’d completed the Iditarod dog race. He’d set dozens of records for speed sailing and had even flown a glider into the stratosphere.

  To some, it seemed unusual that Fossett’s next great adventure would involve Mars science. But he was by no means the first person to experiment with balloons as a way of advancing planetary exploration. Preceding him were several lionhearted Mars explorers, including David Peck Todd, the leader of Lowell’s Chilean expedition. Not long after he returned, Todd announced to The New York Times that he planned to ascend in a balloon to the highest possible altitude a human could reach, wireless device in hand, in an attempt to communicate with Mars. The idea of “hearing” Mars had been very much in vogue. Scientists as prominent as Nikola Tesla and Guglielmo Marconi, the rival inventors of radio communications, had both been fascinated by Mars. Having read Lowell’s reports of intelligent life, they had tinkered with methods for detecting Martian radio signals. Tesla, captivated by the potential to use radio to communicate over unthinkably long distances, once remarked that Mars was only five minutes away by wireless. Todd, however, went further: He enlisted the help of Leo Stevens, a famous aeronaut, to prepare a metal box “made of aluminum for lightness” that he could be shut into. It was fitted with a machine to drive out carbonic acid gas and supply oxygen with air pressure. Todd’s hope was to rise above the crowded airwaves, thereby giving himself the best possible chance of communicating with our near neighbors.

  Even though the Aero Club of New England offered to let Todd use an enormous balloon called the Massachusetts for his Mars expedition, his grand plans never came to fruition. He was slowly eased off the Amherst astronomy faculty after the demise of Lowell’s canal hypothesis, which he had championed. But he still clung to the ambition that radio might bring a Martian civilization within our reach, even convincing the U.S. Army and Navy to shut down all radio communications for two days in 1924 in what became known as “the Big Listen.”

  Nearly thirty years later, another balloonist proposed a still more ambitious experiment. Audouin Dollfus was one of the only practicing planetary scientists in the early 1950s. Mars had been all but ignored for decades, but Dollfus was desperate to know if there would be enough moisture in the Martian atmosphere to support simple forms of life. He had perfected the use of prisms to separate the light of faraway worlds, to measure attributes like water vapor from absorptions in the infrared wavelengths, but Earth’s own atmosphere interfered with his attempts. Like Todd, he was trying to understand Mars in a new way, using waves beyond those our eye could see. And like Todd, he was wrestling with the problem of being stuck on the surface. To answer his question, he would have to find a way to rise above Earth’s damp air.

  Dollfus was a Frenchman—an adventurer at heart, small and slight, with bright eyes and pink cheeks. In 1954, he and his father completed the first astronomical observations from a balloon, but he couldn’t get a measurement of the Martian atmosphere. He concluded that he needed to get twice as high—into the stratosphere. He began building an airtight gondola attached to a telescope with a foot-wide mirror. In 1959, he suspended both from a cascade of over one hundred weather balloons, clustered along a few hundred meters of nylon cable. He insulated the metal sphere of his gondola with foam rubber to protect him from the bitter cold.

  He transported the capsule, slung beneath a French Air Force helicopter, to a military airfield. A flock of assistants inflated his white balloons, filling a field with billowing bags of hydrogen, any one of which could have caught fire. Carefully, they were tied to the long nylon cable in groups of three, extending five hundred meters in length. Dollfus climbed through the manhole, and when the last of the bunch was secure and sufficiently far away, a small explosive charge severed the anchoring cable and sent the cabin into the air. Aircraft approaching Paris were warned not to fret about the strange hazard—what looked like a string of Spanish onions.

  Dollfus launched right around sunset. As he floated up into the stratosphere, he saw a perfectly horizontal line dividing the sky. He wrote in his logbook that the air below glimmered with dust, resembling an almost phosphorescent sea, whereas the sky above was perfectly pure and dark despite the full moon, the constellations shining without scintillation.

  Dollfus spent part of the night at an altitude of fourteen thousand meters—forty-six thousand feet—before a gust of wind caused a group of balloons to burst and the cable to shear. He descended steadily through the darkness, thudding down in a cow pasture near the village of Nivernais. In the end, he still failed to get his measurement, but what a brave attempt he’d made! By reaching those extraordinary heights—decades before the invention of space telescopes like the Hubble—Dollfus cracked the door to studying astronomy from space.

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  AT EIGHTEEN YEARS old, I was completely taken with the idea of the grand gesture. To me, Fossett’s Solo Spirit mission seemed like the next daring adventure, with the potential to change the way we might go about exploring Mars’s atmosphere. Engineers had carefully affixed our aerobot payload to his gondola, which was shipped to Argentina in the run-up to launch. Back in St. Louis, mission control was set up in a tall Gothic building on campus, in what felt like the top of a castle. There were wooden doors and wood-paneled walls, tables with desktop computers, banks of phones, clocks with diffe
rent time zones, navigation books, and tables of data. The aerobot had sensors for position, temperature, atmospheric pressure, humidity, vertical wind velocity. All the raw data from the payload telemetry—everything the white box, gray fan, and wired sensors detected—would be sent back to St. Louis through a satellite.

  When Fossett’s balloon lifted up from a soccer stadium in Mendoza, I cheered wildly in mission control. I could only imagine the sense of excitement and invincibility Fossett must have felt as he soared into the sky. He had all the latest technologies—GPS devices, a fax machine, and a satellite phone. He rode in a futuristic capsule, fashioned from a Kevlar-reinforced carbon-fiber composite. His balloon was a special Rozière design, which utilized novel temperature-control features to keep his helium gas from cooling on chilly nights. He’d attempted this circumnavigation before, but this time felt like his lucky break. I was certain that both Fossett and our little aerobot would succeed marvelously.

  The balloon made swift progress from Argentina out over the Atlantic, arriving in Africa in just a few days, then gliding effortlessly over the Indian Ocean. I traced the balloon’s route on a giant Mercator map, pressing small red pushpins onto the coordinates that the aerobot beacon signaled, as thousands of kilometers away, Fossett gazed upon beautiful vistas. I imagined him transcendently aloft, on the cusp of overthrowing the sky’s “last great challenge,” of finally winning the record.

  The balloon was making fantastic time, and the aerobot was providing a steady stream of information. Geopositional data were relayed every ten seconds, atmospheric measurements every minute. The positioning of an antenna within the center of the balloon had worked extremely well in terms of boosting the signal. Observations matched perfectly with what was observed by satellite data. Ray’s prototype would hopefully experience similar success on Mars one day.