The Sirens of Mars

by Sarah Stewart Johnson

  For years, Mars Global Surveyor monitored changes on Mars: the swelling of the polar caps, the ablation of rock, the disappearance of dust. And, much to Maria’s delight, there were weather reports, relayed by NASA to the public through a website, a weekly window into the changing conditions of an impossibly far place, just like Pickering’s missives from the central mountains of Jamaica. One day, while driving across Massachusetts, Maria even heard two voices on the radio talking about the temperatures and dusty skies up on Mars. They marveled at how one could know such things and wondered who were the scientists that had made it possible.

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  BEFORE THE END of the mission, Mars Global Surveyor also took the first photograph of Earth from another planet. To most people, it was just a footnote, anticlimactic even. It wasn’t Yuri Gagarin peering through his window, seeing our planet from space for the very first time. Nor was it Voyager, turning its camera back from the edge of the solar system to capture Earth as little more than a pixel—in Carl Sagan’s words, “a mote of dust suspended in a sunbeam.” But I remember staring at that picture on my computer. I had searched for it, dragging the image to cover the screen, making it as large as I could. Earth seemed impossibly distant, but it was still recognizable. It was a crescent, more than half dark. The moon was next to us, with the same shadow.

  As I peered at the pixels, trying to resolve the tiny squares of blue and green and white, I thought about where I was in the picture. In the frame, so much had been captured, and obscured. I was there somewhere, going about my life the day it was taken. I wondered if I’d been cooking a white-bean soup or sleeping in a rumpled bed when the shutter clicked, or gazing through the heavy glass window of the library at the rain outside. Perhaps I was sitting under a magnolia tree, or rushing across a crowded city street, midway through an infinitesimal step. Perhaps I was lost in thought somewhere, wondering if I had what it took to be a scientist, wondering who would show me the way.

  Maria was there too, in another pixel. She was no doubt doing great things, unaware of the gravitational force she exerted on the lives of many young women like me. As I sat at my computer, right there on my screen, beneath that image of the crescent Earth, was a message signed with a quote from Tolkien. I had read it again and again: “Not all those who wander are lost.” The message was the reason I’d searched for the image, the reason I was sitting there wondering where I might be the next time a shutter clicked on Mars. It was from Maria, who had written to say that in another few months, I could move to Boston to begin graduate school. She had agreed to become my PhD thesis advisor.

  THE AIR WAS filled with the smell of jacarandas as I waited at JPL visitors’ gate in 2004, marveling at the shimmering posters of spacecraft. I could scarcely believe my luck as I watched the people in cars flash badges to the guards beneath a signpost saying WELCOME TO OUR UNIVERSE. Just the day before, I’d received an invitation from one of my professors to join him and two classmates in Pasadena. They’d been stationed at mission control for several weeks, working on the Spirit and Opportunity rovers, which had landed on Mars in January. Now he asked if I’d like to come to JPL for a few days, just to see what it was like.

  I’d nearly tripped over myself when Maria agreed to let me go. I ran down the stairs of MIT’s Building 54, pedaled past snow on the ground back to my apartment, then raced to Logan Airport to catch a flight. I had with me only my backpack: a pullover, some jeans, and a binder stuffed with notes for my first-year graduate courses in geobiology, Geological Image Interpretation, and Dynamics of Complex Systems.

  The professor who’d sent me the invitation, John Grotzinger—otherwise known as “Grotz”—was one of the world’s best sedimentary geologists. He’d made a well-orchestrated shift into planetary geology, just in time to explore the first sedimentary terrain on Mars. He was tan and thin and tall, and he was intensely inquisitive. When he stared at rocks, he stared like a wolf. His favorite place was among the cliffs of Oman and Namibia, tracking the rise and fall of ancient seas. He loved geology more than anyone I’d ever met. He could pick up any old shale and make it seem chock-full of possibility.

  When he walked into the JPL badging office to meet me, he looked surprisingly disheveled. A “sol” on Mars is slightly longer than a day on Earth, so the science teams had been trying to sync their circadian rhythms with Mars, not Earth. As the sun set at one landing site, the rover beamed a downlink with completed measurements and end-of-drive images of its new location. Based on that data, the scientists would spend the Mars night planning the rover’s next moves. As the sun rose over the rover, a new slew of commands would be beamed to an orbiting spacecraft, Mars Global Surveyor or Mars Odyssey, then relayed and caught by the rover’s antenna.

  Keeping pace with a distant world was not easy, Grotz explained. The rotations of Mars and Earth are similar, and living on “Mars time” just meant staying awake thirty-nine and a half minutes longer each successive day. But it was clear from his exhaustion that the small offset made a huge difference. Every eighteen days, the beginning of the day turned into the beginning of the night. Then, eighteen days later, the beginning of the night was the beginning of the day again. Mission control was slowly pulling away from Earth, then slowly ebbing back, a kind of incessant jet lag.

  I thought about how strange that was—how jet lag hadn’t even been a phenomenon for more than a few decades. Now we were adjusting not only to the spin of our world but to the spin of another. Grotz told me how a watchmaker in nearby Montrose had designed mechanical watches that lost a second every thirty-six seconds, which helped some of the team members keep track. Spirit and Opportunity were on exact opposite sides of the planet. Opportunity’s operations on the fifth floor of Building 264 began just as Spirit’s ended on the fourth, so as one floor of weary scientists would empty into the elevators, the other would fill. Worst was switching between the rovers, he said, which some members of the science team did periodically. That was like waking up in China.

  As we walked across JPL’s campus, he brought me up to date on the mission, which was designed to understand the history of water on Mars, to probe the planet’s rocks and soils for clues to a warm and wet past, and to follow the water to life. The rovers were the size of golf carts, identical to each other and both far more capable than little Sojourner had been.

  Cocooned in inflatable airbags, they had bounced to rest on opposite sides of the planet, with Spirit landing first, then Opportunity three weeks later. Spirit touched down in Gusev, a crater about the size of Connecticut, at the edge of the northern lowlands. Snaking its way into Gusev from the southern highlands was one of the largest channel systems on Mars, Ma’adim Vallis. Everyone hoped the landing site would be the remains of an ancient crater lake, that it would prove that there had once been huge open bodies of water on the surface of Mars, but the rover came to rest on a plain of pure lava. It was a “basalt prison,” battered by dust and incessant crosswinds. On the horizon, some promising hills poked through, but it would take months to reach them.

  Opportunity fared far better. It had been sent to Meridiani Planum, one of the safest places to land on Mars. It was so smooth that some of the scientists worried there would be nothing interesting to see. It too seemed promising for water, though less promising than Gusev. From orbit, Mars Global Surveyor had spotted an iron-oxide mineral called gray hematite, shining like a beacon. It was a crystalline form of rust, a sign that the surface might have interacted with water. It wasn’t a sure bet—magnetite in volcanic lavas can transform into hematite without water being present—but it proved too beguiling to resist.

  After glancing across the surface and rolling to a stop, Opportunity unfolded like a piece of origami. The solar panels flapped open. The paddle of the high-gain antenna tilted to the sky, and just before the wheels clicked into position, the navigational camera began snapping black-and-white pictures.

  As th
e first image appeared on a screen at JPL, the team began clapping. But Maria’s friend Steve Squyres, the Cornell geologist who was now in charge of both rovers, couldn’t get his bearings. As he looked at it, he felt completely disoriented. Where were the rocks? Every last picture taken from the surface of Mars—from Chryse and Utopia to Ares Vallis and Gusev—had been strewn with rocks, filled with the kind of things a rover could study. The first image beamed back to Earth was grainy and rear-facing, but it was clear enough to make out the dents of the bounce marks in the uniform dark soil. They were the only recognizable features. Perhaps the doubters were right about Meridiani.

  When the second image appeared, a forward-facing Navcam, Steve stared at it impatiently. It was underexposed, too dark to make out. As one of the engineers adjusted the contrast to make it more visible, the room grew strangely quiet.

  Suddenly, tessellations of bedrock appeared out of nowhere, a jaw-dropping, beautiful wall of bedrock. The team erupted—there was laughing, cheering, crying, people jumping up and down. Steve could barely get his breath as a voice announced, “Welcome to Meridiani. I hope you enjoy your stay!” It was the first time anyone had ever seen bedrock from the surface of Mars. Sure, there were rocks at other landing sites, but those rocks could have come from anywhere. These rocks had been formed in Meridiani. And they had been formed by water.

  They looked just like water-lain sedimentary rocks—in other words, the kind of rocks that tell a clear geological story. For Steve, it was too good to be true. He had advocated for Meridiani over a hundred other sites because he hoped to find evidence of water, but in his heart, he never dared hope that he would actually discover what he was looking for. He was almost afraid to believe it. He stumbled to the front of the room and said, “I will attempt no scientific analysis…holy smokes, I’m sorry, I’m just, I’m blown away by this.” Someone yelled, “Did we hit the sweet spot?” Steve stammered, “The sweetest spot I’ve ever seen.”

  Up until that moment, no surface mission had ever observed water-lain deposits on Mars; there had been no stratigraphy to investigate—no layers, no relationships among the layers—and therefore no way to investigate how the geology and the climate and Mars might have changed over time. Sedimentary rocks that we could poke and probe were the holy grail. Finally, we could really peer back through time.

  As other Navcam images came down, however, the horizon seemed strangely close, and it was impossible to get a sense of scale. The team tried looking at the images from different angles, struggling to figure out exactly what they were seeing. Slowly, it dawned on them that the airbags must have rolled to rest in the depression of a small impact crater. A crack about the interplanetary “hole in one” led to the crater’s name—“Eagle,” for two strokes under par. And then, when Opportunity finally kicked into gear and began to approach the bedrock, the team’s perspective shifted again: The feature they had called the “Great Wall” became “Opportunity Ledge.” As it turned out, it was barely ankle-high.

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  JUST AS MARS Global Surveyor had predicted, there was hematite everywhere at Meridiani, another line of evidence for water, but not in a form anyone had expected. The hematite had collected on the surface like a spray of ball bearings. The pictures of the ground looked like the kind of cartoonish surface Fred Flintstone might slip on. The spherules were gray-blue in the color-stretched images, so they were dubbed “blueberries.” It was a perfect name—they were also spread throughout the rock just like blueberries in a blueberry muffin.

  At first, the team wondered if the “freaky little hematite balls” were raindrops of metal that had erupted volcanically and been lobbed into the freezing air, solidifying mid-flight before falling back to the surface. But they weren’t all in a single layer, like a layer of ash; many were also buried in subsurface sediments and evenly spread apart. And if they were made by a volcano, where was the volcano? Then another idea emerged: perhaps they were concretions, little metal balls that had swelled from a point of hematite in the subsurface. Slowly, more hematite could have globbed on, forming layers upon layers, like pearls inside oysters.

  The infrared signatures also argued against a volcanic origin, instead suggesting that the hematite had formed in the presence of cool percolating groundwater. The blueberries strewn across the landing site were small, the size of peppercorns, and they were relatively uniform, indicating that the same amount of groundwater was probably present for the same length of time throughout the region. After the water table receded, wind continued to beat away at the surface, eroding the soft surrounding rock. Slowly, the blueberries would have fallen out of the rock and rolled onto the ground.

  The bedrock and blueberries weren’t Opportunity’s only early discoveries: There was also magnesium sulfate everywhere, like Epsom salts in a bath, stretching in every direction, likely deposited in a lake or shallow sea. And there was another kind of sulfate, one that was even more surprising. Not long after landing, Opportunity had driven up to a rock called “El Capitan,” drilling into the rock’s interior with its tiny grinding wheels. Looking at the data, the team saw what they believed to be the sulfate mineral jarosite. Jarosite indicated highly acidic conditions, which, team members were quick to point out, didn’t exclude the possibility of life—microbes, after all, survived in acidic waters in places like the mines of the Sierra Almagrera and the Río Tinto, Spain’s “river of fire.” Moreover, jarosite was a hydrated mineral, meaning it simply couldn’t have formed without the presence of water.

  There was evidence for standing water too: layers of rock overlapping and cutting into others in distinctive patterns—petrified horizons of sand and sediment that had once washed over one another in shallow rivulets—the same smile-shaped markings that line the bottom of most streambeds on Earth. There had once been salty seas or lakes and streams, with sediments reworked by wind. This was what the Mars science community had been sent to find, the first definitive evidence for liquid water on another planet. When the team looked closely at the outcrops of Meridiani Planum, they could even see ripples in the soft rock.

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  IT TOOK A moment for my eyes to adjust after the elevator opened in Building 264 and I followed Grotz into mission control. The windows were sheathed in thick black vinyl. There in the sunless room, dissociated from time, two dozen scientists sat in high-back blue chairs clustered around tables of computers. Giant screens shone with running clocks, projecting the details of the sol’s timeline. In the middle was a long sleek desk, stretching some three to four meters in length, covered by stacks of orbital images of the landing site. The room felt like the helm of a frigate, sailing through a darkened ocean.

  As I looked around, I saw dozens of scientists I knew, mostly only by name. Then I saw my undergraduate mentor Ray Arvidson, who grinned and asked, “How you doing, kid?” A moment later, Steve strode to the front of the room in a pair of cowboy boots. He tossed up a microphone and caught it again. “Time for ‘sog,’ ” he said. Everyone rose from their seats as I tried to figure out what he meant. SOWG, I would quickly learn, was the Science Operations Working Group, the most important meeting of the day. Still holding my bookbag, I followed the others to a nearby room. In the hallway, there was a bottomless freezer of frozen treats. The gift of a local dessert distributor, Ray told me, tossing me a chocolate Drumstick.

  As the mission’s second-in-command, Ray took a seat behind a little blue placard. He was SOWG chair, the head of the meeting for the day. I slipped into a seat at the back and scanned the room. People were talking about “yestersol,” “solmorrow,” and the upcoming “soliday.” It was at once so childlike—all that dripping ice cream!—and at the same time so full of technical sophistication. The rover’s next measurements were designed to follow up on the discovery of the blueberries—critical to piecing together the history of water on Mars. The scientists and engineers worked alongside one
another for more than an hour, hashing out priorities for the drive and figuring out how to implement them: which specific instructions would be sent to the rover through the Deep Space Network. To the uninitiated, they might as well have been talking in code.

  But then the meeting ended, and the lightheartedness instantly returned. The team was bonded and always orchestrating well-meaning pranks. One morning the MiniTES team—the scientists manning the Miniature Thermal Emission Spectrometer on the rover’s arm—had arrived to find their computers and chairs swaddled in Saran wrap. Then the following day, the Pancam team, which ran the panoramic camera on the rover’s mast, discovered that all the keys had been popped off their keyboards, save for one line of letters: “M-I-N-1-T-E-S.”

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  OPPORTUNITY WAS ON its way to Endurance Crater, and Grotz suggested I stay until the rover arrived. I took up residence on my friend’s Caltech couch, taking taxis to and from JPL, as each sol brought the rover closer and closer to its destination. The crater was as large as a football field, and the team had been eyeing it on the horizon since the early days of the mission. Opportunity was proceeding from one hole that had been punched into the ground to another. It wasn’t the craters themselves that were the jackpot but the crater walls, for they offered a glimpse into the ancient past. They revealed layers that had been stacked like the pages of a closed book, one moment in time pressed close against the next.