Three thousand six hundred feet below the picturesque North Yorkshire coast, or roughly the depth of three stacked Empire State Buildings, sits the Boulby Underground Laboratory, where a cluster of unusual machines peer deep into the unseen shadows all around us. The lab is shielded from disruptive surface-level radiation by thick layers of shale, marl and sandstone, making it an ideal site to search for illusive dark matter particles. But this is not the only scientific mystery being plumbed within its dark and salty depths.
Like Pitch Lake in Trinidad and Tobago, a stand-in for liquid methane reservoirs on Saturn’s moon Titan, or Antarctica’s subglacial Lake Vostok, a proxy for the oceans believed to exist beneath the icy crusts of Europa and Enceladus, the tunnels at Boulby grant access to the subsurface of Mars. It is what space scientists call a “planetary field analog,” a portal that allows them to study distant comets, moons and planets they are unable to visit themselves.
Boulby is an active salt and fertilizer mine. The minerals exhumed here were formed by the evaporation of the Zechstein Sea, an ancient inland body of water inside the supercontinent Pangea, which ranged from modern Britain as far as northern Poland in the late Permian Era, more than 250 million years ago. While the Martian surface has been disfigured by impact gardening (with little atmosphere to burn up incoming rocks), pristine underground evaporites may soon provide us with a record of the planet’s watery past along with any signs it once held life.
When I was a child, growing up a few miles north of Boulby, train wagons full of potash would rumble past on their way to Teesport, from where the potassium-rich minerals would be shipped out to fertilize cropland across the globe. I always wanted to know what else was being unearthed at Boulby, so ahead of my next visit home, I wrote to one of the lab’s senior science technicians. A new set of experiments was being planned, she told me, which is how I found myself at the site entrance early on a cold but clear morning last autumn. After changing into PPE, I was led into a side room for a safety briefing. At 9 a.m. sharp, the lift was scheduled to descend into another world.
Mining And Space
Humanity’s image of the Martian landscape has shifted over time. For the British-German astronomer William Herschel, lecturing the Royal Society in 1784, Mars was a second Earth, a place with “clouds and vapors floating in the atmosphere” and “a situation in many respects similar to our own.” Others, like the American William Henry Pickering, who watched Mars intently from his private observatory in Jamaica, saw Mars as an isolated wilderness, a stormy yet magnificent terrain comparable to the Siberian tundra.
To me, the most memorable vision of Mars was Percival Lowell’s, a zealous and self-funded stargazer who thought he saw signs of an industrial civilization grappling with the loss of its seas by redirecting meltwater from the poles to grow food. “Conditions hold there which would necessitate a much more artificial state of things,” Lowell wrote in 1895. “If cultivation there be, it must be cultivation largely dependent upon a system of irrigation, and therefore much more systematic than any we have as yet been forced to adopt.”
Lowell’s Mars was an automated garden, conceived in an age of grand engineering projects like the Brooklyn Bridge and the Suez Canal. Yet all hope for a botanical Mars — artificial or otherwise — came to an abrupt end when the Mariner 4 spacecraft returned the first up-close images of the planet’s sterile, frozen surface in 1954. Suddenly the only reasonable comparison to be made was with our moon — or with a handful of dead and lifeless places on Earth.
The science carried out at Boulby takes place at the invitation of an Israeli mining concern, ICL Group, which excavates potash, rock salt and polyhalite, a sulfate mineral mined nowhere else that is sold directly to farmers as an organic multi-nutrient fertilizer.
“There’s a synergy between mining and planetary research,” says Charles Cockell, a professor of astrobiology at the University of Edinburgh who has led the MINAR, or “Mine Analog Research” program, at Boulby since 2013. “Miners need mineral detection instruments that are small, lightweight, rugged and low-energy, which is exactly the same qualities you’d want for spacecraft instrumentation.”
After being issued with something called a “self-rescuer,” a fist-sized metal box I was told I could breathe through “for up to two hours” in the event of a carbon monoxide leak, I joined a group of visiting students, scientists, technicians and miners to head for the lift. Everyone was dressed in the same outfit: pumpkin-colored workwear, hard hats, ear protectors, steel-toed boots and shin guards known as “spats.” In addition, the miners clutched red 130-ounce water canteens. The rest of us were given lunches in brown paper bags.
It was cold — and loud — as we passed through a series of airlocks. Chit-chat was silenced by the roar of an enormous fan pumping air through the 620-mile tunnel system, much of which stretches out under the frigid North Sea. “Don’t be daft in the shaft,” a sign warned. “Act your age when in the cage.”
As we fell, suspended by a single black cable, the din began to fade. It was completely dark, so one by one we switched on our headlamps. The rising waves of geothermal heat came as a relief.
Pick Your Question
In much of fiction, as in geology, the progression downward represents a journey back in time, whether through the Earth or a human spine. “Each one of us is as old as the entire biological kingdom,” insists Dr. Bodkin in J. G. Ballard’s classic novel “The Drowned World” (1962), a creative use of analog superimposition in which a climate-changed London is submerged in a Triassic-era lagoon. “The further down the central nervous system you move, from the hind-brain through the medulla into the spinal cord, the further you descend back into the neuronic past.”
Such forays were common in the 19th century, when any cave, fissure or even cellar door might hold the keys to a lost city, mushroom forest or prehistoric ecosystem, sequestered inside a Hollow Earth. “I felt as though I were on some distant planet, Uranus or Neptune, witnessing phenomena quite foreign to my ‘terrestrial’ nature,” reports Axel, the reluctant narrator in the 1864 novel that catalyzed the genre, Jules Verne’s “Journey to the Center of the Earth,” while gazing at electric storms above a subterranean sea.
The lift takes seven minutes to descend. When you step out onto the powdery ground, the first thing you notice is the heat, which averages 104 degrees Fahrenheit. The second is the taste.
The saline environment instantly dries up human mouths, but nonhuman life is quite at ease. Extremophile halophiles — or salt-adapted microbes — thrive here in fractures and brine pools, sustained by water from an aquifer above and oils rising from the remains of a Carboniferous forest below.
In his “Principles of Geology” (1830-33), the Scottish geologist Charles Lyell proposed that to comprehend Earth’s deep history, we ought to compare evidence of past events with processes ongoing in the present. In the first half of the 20th century, astronomers and geologists extended this “uniform” view of geophysical processes beyond our atmosphere. Studying impact craters on Earth enabled them to see that the moon was a ledger of past collisions — not the world of gargantuan volcanoes that had been previously assumed.
Once inside the polished, air-conditioned lab, we changed into paper overalls and slippers — the correct attire in which to meet a family of immense yet sensitive machines.
Less than 5% of the known universe is visible to us. Of what remains, 68% is thought to be dark energy and 27% dark matter — particles that do not emit or reflect light but which clump together to influence how galaxies form.
The search for dark matter at Boulby began in the early 1980s with a single table-top experiment run by a physicist from the University of Sheffield. Forty years later, the huge facility contains a suite of pioneering interceptors — sophisticated “nets” designed to catch antisocial particles if and when they interact with nuclei in a gas-based medium.
To protect the machines from cosmic rays and other disruptive forms of radiation — in addition to more than half a mile of rock above — most are housed inside their very own “castle,” a shield made from metals like aluminum, copper or “ancient lead.” This prized commodity can be acquired by smelting warship cannonballs that have lain on the ocean floor for centuries. Because water is surprisingly effective at blocking radiation, the lead boasts a purity that other metals lack.
“Every year you don’t find dark matter, it’s like you’re eliminating suspects from your crime,” says Sean Paling, a cheerful particle physicist who began his career in medical imaging and is now director and senior scientist at Boulby. “CERN is the most expensive machine humans have ever built, and yet they’re only trying to prove dark matter can exist by cooking it in their own kitchen. We’re trying to prove it does exist and is all around us. I’m biased, of course, but to me this is far more profound.”
In the 1990s, the team at Boulby pioneered a technique to increase the odds of catching rare particle interactions using dense liquid xenon as a scintillating (light-emitting) medium. The method would later be integrated into the most sensitive dark-matter detectors on Earth, like LUX ZEPLIN, better known as LZ, which contains seven tons of liquid xenon and lives about a mile underground in a former gold mine in South Dakota.
Another experiment currently at Boulby, known unofficially as a “muon tsunami,” looks like little more than a set of strip lights. These plastic tube-shaped detectors are tracking muons — elementary particles that are created when high-energy protons hit the Earth’s atmosphere and pass through the planet at almost the speed of light. Because muons are more likely to stop and decay as they pass through dense matter, detectors can monitor their “flux” to check for fractures hidden within infrastructure or to create x-ray-like maps of hidden places like pyramids or vaults.
A version of the instrument, TS-HKMSDD, is currently installed in the Aqua-Line expressway tunnel under Tokyo Bay, where it monitors the height of the tide for signs of a tsunami. At Boulby, which is much deeper, the team will test whether it can produce an image of the tide — and even individual waves — as water rolls over the beach.
The first time an analog of a non-Earth environment became a tool for space science was at the moon-like Meteor Crater outside Flagstaff, Arizona. Throughout the 1960s, NASA and the U.S. Geological Survey sought new landscapes, from Mexico to Iceland, where exposed strata, impact features, lack of vegetation and, above all, isolation, would prepare astronauts for life in outer space, and to identify what they saw when they got there.
Soon after its inception, NASA began handing out grants for life-detection instruments. One device, developed by a shy Jewish émigré from Berlin named Wolf Vishniac, was cut from the Viking mission due to budget constraints. Determined to prove its usefulness, the “Wolf Trap” was deployed in the Mars-like deserts of East Antarctica by Vishniac himself — then considered uninhabitable.
The mission cost Vishniac his life. He died trying to recover equipment that had fallen into a crevasse. But when colleagues examined a set of porous sandstone rocks sent to his bereaved wife, they found an army of dazzling blue-green algae taking shelter in the stones.
After the Apollo missions, knowledge of lunar geology improved, and analog sites on Earth were reshuffled and refined. Thanks to spectroscopic remote sensing and data collected during U.S. and Soviet flyby missions in the 60s and 70s, exobiologists and astrobiologists (who study life in the universe) knew they should look for terrestrial regions rich in iron and salt, since both had been detected in abundance on Mars.
“Planets and moons are big places,” says Louisa Preston, an author and astrobiologist at University College London who studies life up close in extreme habitats like Iceland’s notorious Eyjafjallajökull volcano and Hawaii’s Mauna Loa, which erupted last November for the first time since 1984. “We know that, on Mars, we are looking for areas that show signs — morphological or mineralogical — of once having flowing water and sources of energy; on Earth, places such as these support life as we know it.”
Life exists almost everywhere on our planet. Bacteria metabolize in the acidic, iron-rich Rio Tinto in Spain, an analog for waterways on a much younger Mars. Microorganisms teem inside deep-sea hydrothermal vents where no sunlight has ever fallen, and flourish well above the troposphere, higher than commercial airplanes fly — an analog for the temperate realm above Venus’s surface which NASA hopes to study using stratospheric air balloons.
“There’s no environment that’s exactly like Mars or an icy moon,” says Cockell. “Earth has been covered in an oxygenated atmosphere for 2.5 billion years. But if you pick the scientific question right, you’ll always find a site that approximates in some way to an extraterrestrial environment.”
One alternative to using Earth itself as a laboratory is artificial simulation chambers, which are more comfortable for scientists (they’re generally in cities) but can be even more extreme for the microbes under review.
For example, the German Aerospace Centre has three facilities in Berlin capable of simulating temperature and pressure conditions for Venus and Mercury (900+ degrees Fahrenheit), Mars (-100) and various icy moons (almost zero kelvin, the coldest possible temperature). Yet exploration in the field brings together a range of humans from different scientific backgrounds to a single, unpredictable point — and the arrival of new questions is inevitable.
“For me, natural sites are ideal — you cannot constrain them,” says UCL’s Preston. “It is untargeted research. You don’t always know what you are going to find and have to adapt your own ideas and experimental protocols accordingly — just like we would on an alien world.”
Time Capsule
After lunch in the lab’s mess area, we headed to the Mars Yard, a cavernous expanse where prototype rovers trundle across the dusty floor wielding experimental drills, hammers, cameras and sample bags. Sixth on NASA’s technology readiness scale is the requirement that tools be tested in a “relevant environment” — that is to say, an analog.
“Look there,” says Thasshwin Mathanlal, an engineer from the University of Aberdeen who works with lidar, infrared and complex algorithms to outfit drones and rovers that can swoop into dark places (on Earth or Mars) and make 3D maps without getting lost. “We don’t know exactly what they are — but they’re not manmade,” he says, shining his flashlight on a flat black polygon, implanted on the roof, observing us. The anomalous, curiously well-defined shape is a biosignature: evidence of biological processes taking place here long ago.
A recent paper in the journal Astrobiology found that Deinococcus radiodurans (a microbe known affectionately as “Conan the Bacterium”) can endure up to 28,000 times the gamma and UV radiation that would kill a human. The study also found that Conan could in theory survive dried, frozen and buried below the Martian surface for hundreds of millions of years.
“There’s a program between us and NASA’s Jet Propulsion Laboratory that I like to think of as microbial forensics,” explains Paling, the lab director. “They basically want to study a range of ‘dead bodies’ of different ages so they know what to look for when they get to Mars.”
One way to do this is by mapping hidden surfaces for traces of biogeomorphology, or landforms created by life, as Mathanlal and others hope to do. Another is to extract fluid inclusions — small drops of liquid trapped inside minerals as they form — in the hope they will contain organic molecules like lipids, fossilized nucleic acids or other signs of past life.
Perched on the San Rafael Swell in southern Utah, the Mars Desert Research Station (MDRS) is the longest-running Martian analog on Earth, founded by the Mars Society in the early 2000s at a time when NASA seemed to have given up hope of sending humans beyond low-Earth orbit. The site was discovered by scouts working for the director James Cameron, searching for the perfect location to shoot an IMAX Mars movie.
No human has been to Mars, and yet narratives of planetary exploration are already well established in our culture. While in residence at MDRS, participants experience red Jurassic geology similar to that on Mars, but also simulate being there by donning cumbersome EVA suits and sleeping at close quarters in a two-story habitation unit.
Travel magazines, science blogs and clickbait farms compile long lists of “amazing places on Earth that look like alien planets,” many of which overlap with the rare elemental, electrochemical and geophysical compositions sought out by astrobiologists to generate biosignatures that will guide the search beyond Earth or to forage samples they can bring back to the lab. This is work at the limits of what we know, and creativity plays an integral role.
“Analogy is useful — but can never give us all the answers,” says Vincent Ialenti, an anthropologist who writes about how humans have used geological analogs to assess sites for burying nuclear waste. “The experience taught me something about optimism versus pessimism of the intellect. Some people are more comfortable making the leap of faith to bridge time and space and pull together two disparate objects.”
The landscape photographer Andrew Studer uses drones to present “otherworldly” locations in the Western U.S. He describes them as “unique places that made me feel like I was visiting an alien planet.” The footage follows a single “astronaut,” a friend of Studer’s in a costume, who appears like the Romantic rückenfigur, or wanderer, in a sublime encounter not so much with an alien planet, but the ongoing process of discovering Earth as just one planet among many.
Astronomers believe there are perhaps 100 billion galaxies in the universe, each containing about a billion trillion stars, many with one or more planets orbiting them. It seems statistically unlikely that ours is the only one that has produced replicating, thinking, dreaming chemistry. And yet as far as we know, we are a sample of one. As our understanding of life on Earth becomes more sophisticated, our chance of finding it elsewhere improves too.
Before heading back to the surface, it was suggested that the students grab a salt crystal as a souvenir. I decided I would like to be included in the fun and began sifting the sandy floor in search of hidden gems.
As we waited by the lift, a team of miners returned from the rock face, their skin covered in a thick layer of whitish salt, ready to trade places with the upcoming shift. One of the students held up a large translucent stone to be inspected by senior science technician Emma Meehan, a former horse-riding instructor who arrived at Boulby to work part-time as a cleaner and has since risen to become one of the facility’s brightest talents. She took the lamp from her helmet and set the stone on top so that the light shone through. She pointed to three small bubbles suspended in the crystal — 250-million-year-old droplets from a long-dead ancient sea.
It may be a cliché, but returning to the surface really did feel like waking from a dream. It was a beautiful, cloudless day. Everyone laid out their samples on the conference room table and sat around dazed, squinting at each other, before changing back into everyday clothes.
Later, I drove up the coast to Teesside, the once-booming industrial region where I was born. Even in the 1990s, we would occasionally receive instructions to stay home with the windows tightly shut due to a dangerous chemical release or escaped plume of toxic smoke. All through my childhood, the sky at night glowed orange thanks to the flaming towers of the local chemical and steel works, a landscape that inspired the opening scene in (local-born) Ridley Scott’s celebrated sci-fi noir “Blade Runner” (1982).
Although the heavy manufacturing and processing have largely disappeared, the region is undergoing something of a renaissance, and will soon house a lithium refinery, wind turbine production and possibly a factory that makes small modular nuclear reactors — a future nobody of my father or grandfather’s generation would have predicted.
There’s a cynical view of the search for extraterrestrial life expressed neatly in Stanisław Lem’s “Solaris” (1961) as the “space era’s equivalent of religion: faith disguised as science.” But seeking (and analogy) is fundamental to both science and art, and suggests an openness to new information with the potential to change us beyond recognition.
There is a NASA poster in Boulby’s Mars Yard that asks, “Life: What is it? Where is it? How can we find it?” The same question could be asked of dark matter. Terrestrial analog sites have already proven that life, once established, can adapt and flourish in the most punishing environments. By exploring its boundary conditions on Earth, we inch ever closer to the thing we’re studying, which is integral to explaining what we are.
