Over the past few decades the search for life beyond Earth has entered a new phase. Some models have suggested that perhaps a hundred million planets in the Milky Way might hold complex multicellular life. We have learned too that planets need not closely resemble Earth to potentially harbour life; subsurface oceans on distant moons like Saturn’s Enceladus and Titan, for instance, could support microbial organisms. The universe, Cabrol told me, is probably full of such simple life, and the purpose of this expedition would be to refine methods of finding it – of detecting biosignatures. These are signs of life, or lives once lived: organisms, or the structures they have made, even the chemical compounds they have produced.
Over the next few weeks, we would visit five sites at varying altitudes. The higher we climbed, the further we’d go back in time – not on Earth, but on Mars. The high-altitude sites are water-rich, with a thin atmosphere and high levels of UV radiation. They resemble Mars at the beginning of the transition it underwent three and a half billion years ago, when solar winds began to strip away its atmosphere, allowing cosmic rays to reach its surface, and the water that once flowed there vanished into space or was locked deep underground or at the planet’s poles. During this period, any life on the surface would have died or taken refuge in the same kinds of places in which life exists in inhospitable regions like the Atacama. The surface of Mars is exposed to harmful radiation; no life can survive on it today, Cabrol told me, but it might still be hiding underground. The salty, arid sites we visited first were terrestrial analogues for present-day Mars.
For Cabrol, there is much more in the search for life on Mars than answering the old question, ‘Are we alone?’ Billions of years ago, rocks thrown off by comets and asteroids colliding with Earth reached Mars, and vice versa. Perhaps some carried early life. Finding evidence of the transition from prebiotic chemistry to life here on Earth is impossible, because any such records were long ago destroyed by the Earth’s rapid geological activity, by erosion and plate tectonics. But ancient rocks from the time Mars’s crust cooled down are still present on that planet’s surface; if we share our ancestry with Mars, traces of our own life might still be found there. ‘Mars may hold that secret for us,’ Cabrol says. ‘This is why Mars is so special to us.’
It’s October 2016, and Cabrol is in her second year of leading the SETI Institute team on a biosignature-detection expedition to Chile. A stiff Pacific breeze blows dead mimosa blossoms across the pavement as I climb inside a minibus to join them on the long drive to our first field site, where the team had scheduled three days of sampling and working on the problems of how best to find signs of life. Through the blue-tinted windows, the soft yellows and buff oxides of weathered rock and sand are turned a dusty, livid red. Fredrik Rehnmark, a mechanical engineer from Honeybee Robotics, is fizzing with delight. ‘If they built a road on Mars, it would look like this!’ he exclaims.
We drive north, passing pale rocks arranged into the patterns of names and initials on hillsides. Almost nothing moves in this desert. There are places here that haven’t much changed in five million years. Those names written in stone are a kind of biosignature that will outlive not just the people who set them there but all of us and all we know.
Salt begins to spread along the edges of the sandy road as we turn inland. Time drifts. Everything outside the windows is so featureless it seems like a theatrical backdrop. At the site, we set up tents on the shores of Salar Grande, a nine-mile-long salt flat that was a lake millions of years ago. There are flats similar to this on Mars.
The salty air makes my face twitch and burn; I blink constantly. The hyper-arid core of the Atacama is far to the east; here, fog rolls in from the Pacific and has shaped the landscape around us. Close up, the salt flat is composed of broad polygonal plates whose edges are heaped with something that looks like half-melted lemon sorbet, or the dirty, refrozen snow that collects along the roadside in winter. Other salt nodules are heaped in piles like dry and dirty bones, and the ground behind our tents is littered with the detritus of long-abandoned salt-mining operations: boots, open sardine cans, scraps of newsprint, corroded lumps of metal.
Drills echo in the morning air. The engineers from Honeybee are excavating salt cores to test prototype tools for future rovers. A team from the University of Tennessee deploys a drone to map the terrain, a tiny dark star that sounds like a distant nest of wasps. The SETI Institute research scientist Pablo Sobron is analysing salt samples with a laser spectrometer; one will be a feature on future rovers. And students from the Catholic University of the North in Antofagasta are out collecting salt nodules for microbiological lab analysis with the SETI Institute and NASA scientists Kim Warren-Rhodes and Alfonso Davila.
Cabrol picks up a chunk of salt and holds it to the light. ‘Look,’ she says. Inside the nodule are two bright bands of colour: pink on top, green below. These are communities of halophilic – salt-loving – microbes that can survive this extreme environment only by living inside translucent nodules. The green bacteria photosynthesise nutrients from the light filtering through the pink colony above. The pink pigment works as a sunscreen, protecting both colonies from UV radiation that would otherwise damage their DNA.
I’m humbled. I’ve been walking on these nodules all day, and I hadn’t seen the life beneath my feet. ‘Habitability is not something very obvious,’ Cabrol says to me. ‘It can be hidden.’ I look at her slight figure, the salt dusting her gloved fingertips, the faintly mischievous smile on her face, and then stare out at the vastness of the landscape around us. It’s dizzying to think of the scales her work spans: millions of miles of space, billions of years of planetary evolution, the vastness of the universe, the canyons and valleys of Mars, the expanse of salt here, our small forms standing upon it, and these exquisitely tough, tiny, almost invisible signs of life held between finger and thumb.
An only child, Cabrol spent a lot of time alone in her family’s small apartment while her parents worked, and in her solitude she created an imaginative, hermetic world of her own to live in, filling her hours with words and symbols and numbers, writing stories and tracing lines upon atlases. She told me that as a child she had a talent for connecting things that were not obvious to others. She believes that this is still one of her greatest strengths as a scientist. But even as she started to apprehend the vastness of space, her social world remained circumscribed. ‘For a long time,’ she said, ‘I thought that I could do without interacting with others. I didn’t have many friends at all, and I didn’t look for them. I had enough. I was busy enough in my mind.’ Her parents saved to buy her astronomy books and magazines. Her mother understood her passion. Her father was less certain. ‘For him, that was a phase, you know?’ she said wryly. ‘That was a phase that lasted a long time!’
Cabrol’s teenage years were troubled. Things were difficult at home, where her parents were fighting; she didn’t fit in and was bullied at school. Some of her schoolteachers thought she lived in a fantasy world. Although she wanted to study planetary sciences, she studied the humanities, for until she taught it to herself later in her career, maths was not her forte.
Cabrol was taking earth sciences in her final year at Paris Nanterre University when her lab director suggested that she visit the historic Meudon Observatory south of Paris to meet Professor André Cailleux, a pioneer in planetary geology. Cailleux showed her maps of Mars and explained that his colleagues were working on the history of water on the planet. Would she be interested in joining them? ‘All these years I thought I was going 180 degrees from where I needed to go, but the path was taking me exactly where I needed to be,’ she told me. Stepping out from that first meeting, she gazed around at the observatory domes and felt them strangely familiar. ‘All these domes I had been drawing as a little girl, always repeating the same landscape, the planetary landscape, of a planet that was completely desert. And with Saturn in the background, always a dark sky and domes.’ At Meudon, she had finally found a way to get nearer to Mars.
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bsp; During the day she worked on her master’s degree on the evolution of water-carved valleys on Mars, but she spent her nights looking through Meudon’s famous nineteenth-century telescope, the Grande Lunette, dragging a sleeping bag there to rest between hours of observing. Through the eyepiece, there was Mars. It was small, and at first she couldn’t see much, but the more she looked, the more she saw on the dusky, changing face of the planet that would become a focus of her career, a planet whose gullies and dried lakes have become as familiar to her as the backs of her hands. And it was at Meudon too that she had a moment which left an indelible mark. Professor Audouin Dollfus, the eminent astronomer who had discovered Saturn’s satellite Janus, asked her if she would like to see moon dust. ‘Duh! Do I want to see lunar dust?!’
He produced a small container from a safe, and Cabrol looked at it and was disappointed. ‘I had a feeling like: So? That’s it?’ she told me. Politely enthusiastic but secretly unmoved, she left the lab to go home, but when she looked up and saw the moon hanging bright over Paris, she was stricken with awe. ‘All of a sudden this moon dust that looked like nothing looked like the most precious thing ever,’ she said. ‘Because it is not so much what it is but the journey it took to get here.’ It was a revelation. ‘I don’t think that anything I saw through an eyepiece told me the same thing: the journey it took, the spirit of exploration, the danger of exploration, the things you have to accept, that there is a sacrifice, and the sacrifice might be your own life.’
Exploration lights her imagination. ‘I breathe it, imagine it every day of my life, and I dream about it at night,’ she wrote recently in a private manuscript. She told me of a childhood memory: her father carefully opening prickly sweet chestnut cases for her to uncover the glossy, marbled nuts inside. She was entranced. Early moments like this planted the desire for discovery inside her, an urge to find again the wonder of seeing hidden things brought to light.
While working on the question of how flowing water formed lakes on Mars for her Ph.D. at the Sorbonne, Cabrol met Edmond Grin, an eminent retired hydrogeologist who had gone back to earn a Ph.D. in astrophysics. ‘This is his thing,’ she told me. ‘When he has nothing to do, he plays with Einstein’s equations.’ She was twenty-three and he was sixty-six when she first saw him talking to a professor before her class began. ‘For some reason,’ she said, ‘I could not look in any other direction. I was stuck. I was looking at him, and at that time in my brain, that was like: I know this man. I know this person. From where do I know him?’ He sat near her in the class, they looked at each other and: ‘That was it – it took us, you know?’ she said. ‘I cannot explain, but I was waiting for him to show up.’
In the years that followed, Grin helped focus her work and her research methodology and was a transformative presence in deeper ways. ‘He did a magical act on me,’ she told me. ‘From being an introvert writing those codes and symbols and novels and papers, it’s like he took a glove and turned it inside out, and all of a sudden everything that was inside came out.’
When Cabrol travelled to NASA’s Ames Research Center in Silicon Valley in 1994 to work on a landing-site study for a proposed mission to search for life on Mars, Grin went with her. All they took with them was one suitcase, and inside it was a map of the 100-mile-wide Gusev Crater on Mars, made of taped-together photocopied images from the Viking mission, the unmanned spacecraft that surveyed and landed on the planet in the 1970s. ‘The two of us had to take a very big leap of faith,’ she said. More than thirty years after their first meeting, they are still together, still inseparable, now married. In 2010, they edited Lakes on Mars, the first academic book on the subject. Cabrol calls him Merlin, after the magician. He has grown frail now, and this is the first time Cabrol has been to the Atacama without him. That he had to stay behind is a source of deepest sadness for her, something that I realise only later in the expedition, when she leaves the group at a lookout near San Pedro de Atacama to walk down an incline and gaze at the pyramidal, distant slopes of Licancabur, a volcano they once climbed together. She tilts her head to one side and doesn’t move for a long time. She looks small and terribly alone.
We move south, up on to the Altiplano, the second-largest plateau on Earth, where the landscape has an astonishing luminosity; it glows like a scene painted on fine bone china. It’s wetter, too; there are golden grasses on the hillsides. When Cabrol first came to this place and saw the snow-capped Andes, it was a shock. She felt, she told me, as if she were back somewhere she belonged. There was a connection, just as when she first saw the Atacama Desert through a live feed from an experimental rover, its arid landscape projected on to a screen in a science-operation room. Even with that distance, that robotic mediation, she said, ‘the love story started’, and ‘there was something that I knew was drawing me to this place’.
She has a similar affinity with the Gusev Crater, into which water may once have poured from the immense canyon of Ma’adim Vallis. She and Grin studied it and chose it as a landing site for the Spirit rover. ‘I had the same feeling when I first saw Gusev from the surface. I was the first person on the planet to see a new landscape. And you don’t get over this. You cannot. I will die with these images. It’s in me for ever.’
On one of our long expedition drives, Cabrol stares out of the window, shoulders tensed with what I realise is happy anticipation only when we crest a rise and see the first dark peaks of volcanoes before us. She turns to us all with a blazing smile and announces, ‘I’m home.’
At first, Salar de Pajonales is a distant patch of white between dark volcanic slopes, but as we meet it and drive through its broad expanse of gypsum sands, sunlight flashes across thousands of crystalline flakes, ephemeral points of fierce white light. The salts here are chemically different from those at Salar Grande. Cabrol visited the site briefly five years ago and is thrilled to return and discover what it held. Underfoot, the ground crunches and tinkles; it’s like treading on sugar mixed with broken glass. Huge bosses of gypsum are dotted around us, round structures like crumbling coral, the colour of milk chocolate. Fascinated, I pull out the sun-rotted blades closest to their surface with my hands, as if extracting teeth.
Life is less easy to locate here. Only when Bill Diamond, the SETI Institute’s chief executive, kicks a rock do we find a broken chunk colonised by those familiar microbes in shades of pink and green. Her face half obscured by mirrored glasses and a scarf, Cabrol tenderly uncovers the fossilised imprints of ancient bacterial colonies called stromatolites. They look like pitted fragile cups, chalky finger print impressions. Samples are photographed, noted, bagged to be sent on to the lab. Overhead, the drone starts mapping this terrain, struggling in the wind.
That afternoon, I hop in a truck with a biologist and a biochemist from the Catholic University of the North who want to take bacterial samples from a nearby lake. Its turquoise waters are surrounded with pale gypsum blades like thickets of kitchen knives. It is too surreal; I return to the truck feeling unaccountably blinded, though I can see. It is as if a white light is shining behind my eyes. My nose runs; my sinuses ache. The things I write in my notebook have become increasingly bizarre. I scrawl questions asked in glass across a whole page, an uncanny aide-memoire for something I never remember. As we drive back to the main study site, I see Cabrol in the distance, a slight shadow moving slowly across the pale fire of sunbaked gypsum, something strangely like a mirage of a person.
That night we sleep in an abandoned mining camp. In the early hours, in the rat-dropping-dusted particleboard and corrugated-iron shack we are using in lieu of tents, I lie in increasingly irritated denial until I drag myself out of my sleeping bag to pee. It is minus 0.4 degrees outside. Above me, the Southern Hemisphere stars are all dust and terror and distance and slow fire in the night, and I stare up, frozen, and frozen in wonderment.
Then we climb higher still, to volcanic sites that resemble formations found on Mars, so high that there isn’t enough oxygen for the engine of our minibus. It stalls hal
fway to our destination. We make a U-turn, return to Antofagasta and rent a new minibus. This also stalls. When we finally reach the geyser field of El Tatio, it is deserted. At about fourteen thousand feet, it is one of the highest active geothermal sites in the world. Tourists flock here at dawn, when the freezing air turns the locale into columns of roiling steam. Some geysers are low to the ground and hardly visible, just a faint shimmering of warm air above them; others look like tall berms of clay pouring out thick gouts of steam. This kind of volcanic, fumarolic environment would have been present four billion years ago on Mars, and old hydrothermal environments like it are one of the most likely habitats to hold life, or the remains of former life, on the planet.
Cabrol dons her red-and-black rucksack, black fleece hat and mirrored glasses, picks up a geologic hammer and starts hacking at an inactive geyser. The surface looks devoid of life, but soon she is delighted to discover bright emerald colonies of chasmoliths – microbes that live in cracks and fissures – thriving on the underside of lumps of geyserite. The hot springs here are full of algal mats and organisms which have evolved to live in water that is almost boiling; they glow purple and dark pink in the sun, their colours protection against UV rays.
Cabrol has always been drawn to both volcanoes and lakes, to fire and water. They’re completely opposite, she says, ‘but if they work synergistically together, they create steam, which is a source of energy. And then you can produce power. And you create things with that. But if the water goes on the fire, then you have destruction. And my entire life is just trying to find this balance between creation and destruction. For the things that I create and the things that are eating me inside. And it’s a very fine balance.’ There is a pattern in her life, she tells me, where the highest of highs are swiftly followed by the lowest of lows. She speaks to me of the deaths of her mentors, friends and family members, of times she came close to death, of times when she struggled with inner darkness. ‘What people see in me is the successful woman, the leader, but all of this is built on sweat and work and temper, you know? It’s losses, tragedy, death and tears. I guess you cannot be strong if you never have been hurt and learn how to survive that.’ As she tells me this, she looks bone-tired. It is the third week of our expedition, and she is sleeping badly, two or so hours a night, she says. And the altitude medicine she is taking is making her sick.
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