by Ben Miller
For me, the final nail in the coffin came with the Voyager missions. Throughout the 1980s, wondrously depressing photos emerged as these twin probes flew past Jupiter and Saturn, and Voyager 2 then continued farther, past Uranus and Neptune. Beautiful as each of these four giant balls of gas was, with no solid rock and no liquid water, how could life ever take hold?
We had higher hopes for their rocky moons, but they too were cruelly dashed. The Galilean moons of Jupiter—Io, Europa, Ganymede, and Callisto—ranged in size between the Moon and Mercury, and were every bit as barren. There were a couple of surprises. Io had active volcanoes, busy spewing sulfurous gases, and Europa was as smooth as a billiard ball, but that was about it. With no atmosphere, out in the freezing boondocks of the solar system they were a biological nonstarter.7
With the Jovian moons out of the running, attention turned to Saturn. One of the main objectives of the Voyager mission was to investigate Titan, thought at the time to be the largest moon in the solar system.8 Voyager 1 plotted a course a mere four miles from its surface, but saw only an impenetrable haze. That meant Titan, unique among moons, had an atmosphere, but it also meant we had no idea what was going on underneath. It seemed pointless for Voyager 2 to follow up, so instead it was diverted to take a look at Uranus and Neptune. On its way, it managed to grab a photo of another Saturnian moon, Enceladus, which appeared to be a lump of solid water ice.9
If the moons of Jupiter and Saturn are chilly, those of Uranus and Neptune are bone-numbing. In January 1986, Voyager 2 made it to Miranda, a tiny world less than a seventh of the size of our own Moon, with an average surface temperature of –210°C. It had a truly bizarre surface, made up of a patchwork of cratered and smooth sections, leading some to dub it “Frankenstein’s Moon.” Either Miranda had been smashed and hastily reassembled following an impact, or somehow the gravitational pull from Uranus was warming its interior, giving it the icy equivalent of plate tectonics.10
Finally, in the summer of 1989, Voyager 2 made it to Triton, by far the largest of Neptune’s fourteen moons and three-quarters the size of our own satellite. Like Miranda, Triton was truly alien, and not in a good way. Even its orbit was peculiar. As you may know, the planets and their moons all tend to spin and orbit in the same direction; counterclockwise if you are looking down on the solar system from above. Not so Triton, which orbits Neptune clockwise, betraying the fact that it isn’t a homegrown moon, and was most likely kidnapped from the band of icy rubble outside Neptune’s orbit known as the Kuiper Belt. Although small in comparison to Earth, Triton was geologically active with very few craters, and had a surface made of solid nitrogen. Unsurprisingly, it was also one of the coldest places in the solar system, with a temperature of –240°C.
And that was about it. In the 1950s, we had dreamed of battling angry expat Martians and being seduced by blonde-haired Venusians in a tropical paradise. By the end of the 1980s, it was painfully clear that we were going home from the party on our own. Summing it all up was the image Voyager 1 took on February 14, 1990, as it looked back at the solar system from an orbit halfway across the Kuiper Belt. In a vast expanse of lifeless black, Earth appeared as a single fragile pixel, what Carl Sagan famously called the “pale blue dot.” His words are so well turned they are worth repeating.
The Earth is the only world known, so far, to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment, the Earth is where we make our stand. It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another and to preserve and cherish the pale blue dot, the only home we’ve ever known.
TRAINING THE BEAGLE
The Space Age, which had begun with such optimism, had ended on a cosmic downer. We were alone. Commerce, not exploration, became the driving force behind space science, and the satellite industry boomed. Public interest in space waned, and at one or two dinner parties in north London which I had the misfortune to attend during the early noughties, intelligent and educated people expressed doubt that we had landed on the Moon at all. Internet rumors suggested that mankind’s greatest achievement had been a US government hoax, staged in a movie studio by Stanley Kubrick and shot with TV cameras in a bid to demoralize the USSR and to win the Cold War. The astronauts hadn’t risked their lives; they had all been fakers.
If I had to pick a low point, for me it would be the launch of the Beagle, the life-seeking robot lander that formed part of the European Space Agency’s 2003 Mars Express mission. Just as Darwin’s voyage on HMS Beagle had inspired his theory of evolution, so it was hoped that this plucky little sniffer dog would root out signs of Martian life and rewrite the rules of biology. With a call sign composed by Blur, and a Damien Hirst spot painting as a test card for its on-board video camera, the Beagle was basically Britpop on steroids, and about as long lived.
To be fair, it had an ingenious design. Its mother ship, Mars Express, had only ever been intended to be an orbiter rather than a lander, but thanks to the charisma and media savvy of the UK’s Colin Pillinger, the ESA higher-ups were outmaneuvered and passage secured for a stowaway roughly the size of a bin lid. After jettisoning from the Mars Express, two consecutive parachutes would slow the Beagle’s descent, and three airbags would cushion its landing. Once on the ground, the airbags would detach, the lid of the main housing would flip open, and out would flop four petal-shaped solar panels. A mechanical arm would then emerge, like the stigma from a giant flower, bristling with sampling tools.
Their variety was impressive. As well as the aforementioned video camera there was a microscope, a rock grinder and corer, a wind sensor, a wide-angle mirror and a telescopic drill called the Mole, which was capable of digging up to 1.5m into the Martian soil. Once a sample had been collected, the mechanical arm would then maneuver it into an inlet port in the central housing, ready for a well-equipped on-board lab to identify exactly what types of molecules were present. If there was—or ever had been—life on Mars, there was a good chance that the Beagle would be able to find it.
Touchdown was planned for Christmas Day 2003, and at the allotted hour patriotic Britons waited patiently by their radios and television sets listening out for the otherworldly strains of Blur’s call sign. Instead there was silence. The Beagle had vanished without trace. The smug mediarati of north London were right, it seemed. The Moon landings were fake, and the ineptitude of the Beagle was but so much grist to their infuriatingly self-satisfied mill.
Yet help was at hand. As our interplanetary odyssey languished in the doldrums, a sudden gust of enthusiasm blew in from the most unexpected quarter, driving all before it. While space scientists had focused all their efforts on nearby planets and drawn a series of depressing blanks, their colleagues in the altogether less glamorous world of microbiology had been quietly coming up trumps. Because as it turned out, something akin to aliens had been found, and in the most unlikely of places. They were right here on Earth.
LIFE, BUT NOT AS WE KNOW IT
Tom Brock loved the outdoors. Canoeing and backpacking were favorites, and in July 1964 he paid a visit to Yellowstone National Park in Wyoming. This, of course, is the home of the famous geyser Old Faithful, which every hour and a half spouts scalding hot water over 150ft in the air. It wasn’t this attraction that caught Tom Brock’s eye, however; it was the multicolored scum in the hot springs nearby. Luckily for us, Tom Brock wasn’t just an outdoorsman, he was a microbiologist. He knew a microbial mat when he saw one, and he also knew that they shouldn’t be growing in near-boiling water.
A microbe is the technical name for a single-celled organism such as a bacterium. As the name suggests, individual microbes are too small to be seen with the naked eye, but, given a suitable environment, they are more than happy to club together to form wha
t is known as a mat. The ones at Yellowstone often contain pigments such as chlorophyll, which you’ll know is green, and carotenoids, which can be anything from yellow to red.
Chlorophylls and carotenoids are key players in photosynthesis, the process whereby microbes, plants, and algae use the energy of light to build long-chain carbon molecules from carbon dioxide, known in the trade as carbon fixing.11 The effect at Yellowstone can be spectacular, particularly at the Grand Prismatic Spring, where the deep blue of the central basin is surrounded by concentric circles of green, yellow, orange, and red microbial mats as the water shallows out.
Microbes, of course, are living things, and the conventional wisdom at the time was that they should only exist within a narrow range of temperature. After all, all living things are made of proteins and contain water. Freeze them and they’ll go solid. Heat them and their proteins will start to break apart, or denature, a process that in the everyday world we call cooking. Warm your meat or your microbes to anything above 60°C, and you can expect even the most resilient proteins to become gelatin in your hands.
That, at least, was what we believed back in the 1960s. Yet to Tom Brock’s astonishment, in the broiling pools of Yellowstone, microbes were positively thriving. Soon he had shifted his research to what became known as “extremophiles”—organisms that love extremes. There seemed to be no limit to their audacity; during successive visits to Yellowstone throughout the mid- to late sixties, Brock and his research team found strains of bacteria in the Yellowstone pools that thrived at temperatures as high as 90°C.
Extraordinary as this news was, it was bewilderingly slow to catch on. Truth be known, when it comes to reality, we humans are not the most reliable of creatures. Not only are we capable of seeing things that aren’t there, but we are also capable of not seeing things that are. There were two million visitors12 to Yellowstone Park in 1964, all of them gazing with wonder at the multicolored hot springs. Many of them must have been scientists, and one or two may even have been of a distinctly microbiological persuasion. Yet no one other than Tom Brock spotted what seems now to be glaringly obvious: The scalding waters were festooned with living creatures that really shouldn’t have been there.
Brock wasn’t slow to publish his findings, but, even so, it wasn’t until the late seventies that news of his discovery started to reach mainstream scientific journals. And at that point our story takes another twist. It’s one thing when a diligent microbiologist finds some unusual bacteria photosynthesizing in a hot spring in Yellowstone Park; it’s quite another when geologists stumble across a whole zoo of unfamiliar creatures more than a mile deep in the Pacific Ocean.
THREE MEN IN A DEEP SUBMERGENCE VEHICLE
We should be grateful to Alvin, a three-man deep-sea submersible owned by the US Navy, for two reasons. The first is because in 1966 it recovered an unexploded hydrogen bomb from the bottom of the Mediterranean Sea, after a B-52 bomber collided with a tanker plane while refueling in mid-air. In that case, it may well have averted nuclear Armageddon and the end of the human race. In the second, some would say it found the very place that the ancestor of all life—the human race included—got its start.
The theory of plate tectonics was put forward by the German geologist Alfred Wegener in 1922, and, as you probably know, proposes that the Earth’s crust isn’t static, but is made up of a patchwork of plates, each of which is moving. The joints between plates tend to be where all the geological action happens, in the form of volcanoes, islands, mountains, and trenches. Exactly what you get depends on what’s on top of the plates—ocean, for example, or a continent—and whether they’re being pushed together, pulled apart, or are slipping side by side.
At least, that’s how it usually works. Sometimes, however, you get volcanoes in the middle of a plate, well away from the edge. In these cases, there seems to be something deep beneath the crust, a “hot spot” if you like, which the plate is riding over. As the plate moves, the hot spot punches a series of volcanoes up through it. The Hawaiian islands are the classic example, sitting as they do right in the middle of the Pacific plate, which is currently moving northwest toward Eurasia. As fresh Pacific plate moves over the hot spot, plume after plume of hot magma shoots up through it, creating a chain of volcanoes on the ocean floor. The tips of these volcanoes form the Hawaiian islands.13
Another example, funnily enough, is Yellowstone Park, though in that case we are presently between eruptions, with the last one having taken place around 640,000 years ago. When a volcano erupts, the encircling area can often collapse, leaving a depression known as a caldera, after the Spanish for “cooking pot.” It’s in the caldera from the last eruption at Yellowstone that we now find Old Faithful and the Prismatic Springs. A third example is the islands of the Galápagos, and that’s where the plucky little submarine known as Alvin comes in.
THE GARDEN OF EDEN
On February 8, 1977, Alvin set sail from Panama aboard a purpose-built catamaran named Lulu, heading for a deep-ocean volcanic ridge just north of the Galápagos Islands known as the Galápagos Rift. Once there, the plan was to try and find hot springs. The saltiness of the world’s oceans suggested they were getting a supply of salt water from somewhere, and the smart money said that somewhere down on the sea floor there had to be the equivalent of Yellowstone’s pools and geysers, pumping out salts and minerals. Nevertheless, at the time of Alvin’s dive, no one had yet found a real hydrothermal vent that would settle the issue one way or another.
The previous summer, a survey of the Galápagos Rift had used an unmanned deep-sea camera to hunt for hot springs, but without success. At one point, however, the umpteen photos of barren sea floor were interspersed with a few brief shots of a pile of dead white clam shells, along with a beer can. The team assumed it was just rubbish thrown overboard by a ship having a party, and named the site “Clambake.” After all, nothing could possibly be living at that depth, because there was no light.14 Without light, there would be no plants, algae, or bacteria. And without them there was nothing for anything else to eat.
How wrong they were. On February 17, 1977, Alvin took a dive, piloted by one Jack Donnelly and carrying two geologists, Jack Corliss and Tjeerd van Andel. As they neared the ocean floor, the water began to shimmer. Sure enough, hot water was pumping out of the dark volcanic rock, and forming black sulfurous clouds as it cooled, earning such vents the nickname of “black smokers.” But that was far from all. As Alvin’s searchlights scoured the surrounding rocks, they revealed a ghostly menagerie of extraordinary creatures. There were giant white clams, white crabs, and even a purple octopus, all very much alive. Confused, Corliss picked up the acoustic telephone and called his graduate student Debra Stakes, above them on board Lulu. “Isn’t the deep ocean supposed to be like a desert?” Corliss asked. When Stakes confirmed that it was, a puzzled Corliss replied: “Well, there’s all these animals down here.”
It got weirder. Subsequent dives revealed more hot springs, and even more strange creatures. At another spring they found an orange animal that resembled a dandelion; at another that they breathlessly christened the Garden of Eden, they found a forest of giant tubeworms with bright red tops, swaying in the water like a field of flowers. They did their best to collect specimens, but being a geology expedition they had little in the way of formaldehyde to preserve them in. Instead, they used the next best thing: some bottles of Russian vodka they had bought in Panama. Tjeerd van Andel began to lose interest in his original goal of finding hot springs, and lay awake at night, his mind buzzing with questions. Where had these creatures come from? What could they possibly be eating?
Two years later, in 1979, a team of biologists returned to find out. Alvin was modified with a new collecting basket and a second mechanical arm, and fitted with a movie camera. On each dive, the team returned with a zoo of creatures that had never been seen before: new species of mussels, anemones, whelks, limpets, featherduster worms, snails, lobsters, brittle stars, and blind white crabs. The delicate or
ange dandelion-like creature seen on the 1977 dives turned out to be a relative of the Portuguese man-of-war, though it quickly disintegrated after being brought to the surface. Finally, the mystery of what all these creatures were eating was solved by a biologist called Holger Jannasch. At the base of this baroque food chain was a microbe. Rather than getting its energy from sunlight, this bacterium was feeding on a chemical in the vent fluid; specifically, hydrogen sulfide.
Suddenly, all bets were off. If life didn’t need light, or moderate temperature, where else on Earth might it be lurking? Suddenly, extremophiles seemed to pop up everywhere we looked. We found microbes in nuclear reactors lapping up radiation ten times stronger than that which would kill the hardiest cockroach. We found both fish and microbes thriving under extraordinarily high pressure 11,000m underwater in the Challenger Deep and the Marianas Trench. We found microbes and fungi bathed in acid so strong it has a pH of zero. We even found bacteria that live inside rocks.
All of which raised an interesting question: Who was really living at the extremes, them or us? To a bacterium which lives in the sweltering heat of a Yellowstone spring, aren’t we the extremophiles, able to endure dessicatingly dry surroundings so cold that the little water that is available regularly freezes solid? What was the natural environment of the first life? Had the first cells incubated in the shimmering heat of a black smoker, and only later migrated to cooler, sunlit shallows? If microbes could live in rocks, could they travel between planets on meteorites? Had life begun elsewhere—on Mars, maybe—and taken a joyride to Earth on a space rock?
Life, in short, simply wasn’t what we thought it was. It wasn’t delicate, or precious, or in any way predictable. Far from it: It was tenacious, commonplace, and infinitely adaptable. Here on Earth, all it seemed to require was water, carbon, and a source of energy. Maybe Mars, Venus, and Mercury weren’t quite the inhospitable deserts we had once feared them to be. If they contained even trace amounts of moisture, they might be home to some sort of bacteria. Could some of those icy moons, orbiting giant gas planets in the outer reaches of the solar system, be habitable after all?