Alien Oceans

The Search for Life in the Depths of Space

Kevin Hand

• Publisher: Princeton University Press
• Year: 2020
• ISBN:
  9780691189642
• Topic: Sciences physiques
• Subtopic: Science de l'espace

Inside the epic quest to find life on the water-rich moons at the outer reaches of the solar system Where is the best place to find life beyond Earth? We often look to Mars as the most promising site in our solar system, but recent scientific missions have revealed that some of the most habitable real estate may actually lie farther away. Beneath the frozen crusts of several of the small, ice-covered moons of Jupiter and Saturn lurk vast oceans that may have existed for as long as Earth, and together may contain more than fifty times its total volume of liquid water. Could there be organisms living in their depths? Alien Oceans reveals the science behind the thrilling quest to find out.Kevin Peter Hand is one of today's leading NASA scientists, and his pioneering research has taken him on expeditions around the world. In this captivating account of scientific discovery, he brings together insights from planetary science, biology, and the adventures of scientists like himself to explain how we know that oceans exist within moons of the outer solar system, like Europa, Titan, and Enceladus. He shows how the exploration of Earth's oceans is informing our understanding of the potential habitability of these icy moons, and draws lessons from what we have learned about the origins of life on our own planet to consider how life could arise on these distant worlds. Alien Oceans describes what lies ahead in our search for life in our solar system and beyond, setting the stage for the transformative discoveries that may await us.

PART I

OCEANS NEAR AND FAR

PROLOGUE

THE BOTTOM

We were stuck on the bottom. Batteries were running low. Our air was running out. We had no way to communicate to the other submersible or to the team on the boat some 10,000 feet above us. We were nestled in the metal sphere of our tiny submersible, perched on some rocks at the bottom of the Atlantic Ocean.

This was my first trip to the ocean floor, and it had the makings to be my last.

Yet somehow it seemed peaceful. With what little light we had left I was able to look out through the porthole of three-inch glass and see a long, red creature exploring the surface of a rock, perhaps looking for its next meal. There it was, going about its business, with no concern or awareness of our precarious situation.

It’s easy for things to turn surreal and serene in a tiny submarine. Our brains have no way of processing the reality of the situation: several thousand pounds of pressure per square inch, a landscape revealed only by the limited lights on the sub, odd sounds and whirls of the machine that’s protecting you from a gruesome, watery death. Unlike experiencing a fear of heights or a bone-dry desert, there’s nothing in our Homo sapiens software that knows what to do when cooped up in a metal ball at the bottom of the ocean. We had no connection to a mouthpiece and breathing regulator like scuba divers and had no need for decompression on the way up. In a submersible you simply breathe the air around you. Sure, there’s the potential for claustrophobia with three people crammed into a sphere two meters in diameter and the darkness of a world cut off from sunlight; but if you can get beyond that, it’s really quite nice. That is, if everything is working as it should.

I actually had no business being down there. First, as a human I was clearly out of my biological comfort zone; I needed technology to make this trip possible. But second, and perhaps more important, my professional realm had long been that of the stars, planets, and moons. A childhood obsession with aliens had led me down a path to studying Europa, an ice-covered moon of Jupiter that had recently been revealed to harbor a vast subsurface ocean. I was in the midst of my PhD studying Europa’s physics and chemistry when fellow space nerd and longtime friend George Whitesides rang me to gauge my interest in an exciting project: James Cameron, filmmaker of Titanic, Terminator, and many other successful movies, was looking for a young scientist to talk about Europa while exploring the depths of our ocean. Would I be interested in potentially joining the expedition? It was not your everyday phone call.

The year was 2003 and Cameron wanted to make a film about the deep sea and the prospect of searching for life in Europa’s ocean. The team would explore the seafloors of the Atlantic and Pacific Oceans, studying how life survives in the dark depths—conditions that might be comparable to those found on Europa. My role would be to help connect ocean exploration with the search for life beyond Earth. The deep-sea hydrothermal vents that we would explore serve as chemical oases for life in the ocean’s depths and provide some guidance in our search for habitable environments beyond Earth.

At the time, given where I was in my studies, it was a difficult decision to make. My primary research would have to take a backseat while I was out at sea. Did I want to add this diversion during a time when I was very focused on my PhD? The depths of our ocean are potentially a good analog for what might be going on within Europa’s ocean, so from that standpoint I could at least justify the time away.

In retrospect, it should have been a simple decision. If you ever get the chance to go to the bottom of the ocean, take it. Don’t think twice; just say yes. Your brain will be changed forever.

My own internal deliberations were clarified by the sage words of mentor, musician, and microbiologist extraordinaire, Professor Ken Nealson of the University of Southern California. Standing on a dock one evening on Catalina Island, Ken grabbed my shoulder and said, “You’re overthinking it! If there’s even the slightest chance you get to go to the bottom of the ocean, you better go!”

And so, a month after that phone call from George, I found myself on the Russian research vessel Keldysh, floating above the middle of the Atlantic Ocean, preparing to explore the darkness below instead of the stars above.

The ocean had long been magical to me—not just because of its vastness and great depths but because it was a place with which I was largely unfamiliar. I had grown up in the landlocked state of Vermont. Set me down in the mountains or in a cave and I’d do fine, but the ocean was a foreign environment to me. I wasn’t afraid, per se—there was no Jaws music running on a loop in my head. Rather it was that lack of familiarity: I did not know how to read the clouds and winds, and there would be no trees whispering about the weather, no mountains to break the sky. Only an arc of the horizon, with water from end to end, the world below hidden by the waves above.

I was fascinated. Cruising from the port in Halifax to the middle of the Atlantic Ocean, I spent many hours—day and night—sitting on the bow of the Keldysh, gazing out at the water, trying to build an innate sense of my new environment. But it was alien. The vast expanse of the ocean was well beyond my comfort zone—exciting and intimidating at the same time.

With a combined sense of uncertainty and anticipation, I turned my attention to the machines that would take us into this extreme environment—the Russian Mir submersibles (in Russian, mir means peace or world). I spent time in the machine shop on the Keldysh, communicating with hand gestures and the occasional Russian word. I was eager to get a sense of how the submersibles work—and what could go wrong. I had no idea what to look for in a good sub, but the engineers were very patient. I soon learned that Russian engineers are nothing if not robust and thorough: there was always a backup plan, and a backup to the backup plan, and so on.

The basic goal of the physics of a submersible is pretty straightforward: (1) don’t get crushed, and (2) make sure you can float when you need to. Unlike space exploration, gravity is your friend when exploring the ocean floor. To get back and forth from space requires any number of variations on rocket engines, heat shields, parachutes, and wings. To get back and forth from the seafloor, the general idea is to carry a weight on the way down and then drop it when you want to come up. Although the change in pressure in the ocean is fairly extreme, there’s not a huge temperature difference, and you’re never traveling that fast. As long as your sub can withstand the pressure and is buoyant once you drop the weights, you’ll rise to the top of the ocean like a cork.

The basic underlying simplicity of how a submersible moves up and down through the water was central to my getting comfortable with the Mir subs. Genya, Viktor, and Anatoli—three of the pilots and engineers who endured my questioning—explained the various backup systems and redundancies the subs boasted. For the most part, the subs followed the prime KISS rule of engineering design: Keep It Simple, Stupid. They had relatively few moving parts, and the electronics seemed like hardy relics from the Cold War. Nevertheless, my stream of “What ifs?” eventually led to the worst-case scenario: What if you’re many kilometers down at the bottom of the ocean and your power fails, your thrusters fail, your communications link fails, and you start running out of air? You’re just sitting in a fancy hunk of metal trapped at the bottom of the ocean. What then?

Not surprisingly, there was a plan. In that scenario, you lift up one of the seats in the sub and find a big wrench. That wrench is used to loosen a large nut on a bolt that is connected to a weight. Once that weight has dropped, the sub becomes positively buoyant. It should start to rise off the bottom of the ocean and gradually accelerate as it rises upward. According to the engineers, by the time the sub reaches the surface, it will have amassed so much momentum that it would likely pop out of the ocean and into the air, rising a few meters above the ocean surface. It’s not pretty or high-tech, but at least you’re not dead on the bottom.

All of this was going through my head as we sat stranded on the seafloor in our dying submersible. I was starting to think more and more about that wrench. Was I certain it was under the seat? I should have double-checked before we left.

Up until that point, everything had gone quite well. After reaching our location near the middle of the Atlantic Ocean, we had dived from the ship in two subs—Cameron and two team members in one, me and two team members in the other. Our goal was to explore hydrothermal vents on the side of a seamount called Menez Gwen (basically a volcano on the bottom of the ocean).

Being in a submersible at the bottom of the ocean feels like a hot air balloon ride, scuba dive, and space mission rolled into one. (Mind you, of the three, I’ve only ever scuba dived.) Motions are, for the most part, slow and smooth. The Russian Mir submersibles offer a small (approximately eight-inch) porthole from which to peer out into the depths: one porthole for each occupant, three in total. In the center is the pilot and to the left and right are two passengers. You can’t stand up, but there’s enough room for a cramped, hunched-over shuffle if one person needs to trade places with another. Instruments, buttons, and switches along the interior are reminiscent of the 1970s and 1980s, when these subs were built and first deployed. Seats with blue vinyl cushions form a tiny, communal U-shape, but there’s not enough space for all three people to have their legs on the floor at the same time. Usually, the pilot sits upright in the middle, hands on the control sticks, while the two passengers lie on their sides, which they have to do to peer out the windows.

On the way down to the bottom, when the machine is dropping like a stone, you pass rapidly through the photic zone—the uppermost layer of water, approximately 300 meters deep, through which sunlight shines and in which life thrives off of photosynthetic organisms like phytoplankton.

As you descend through this region, light begins to fade. Blue goes to black. The sub starts to cool. You can’t feel that you’re falling, but the sounds from the acoustic communication system serve as a metronome reminding you of the distance between you and the rest of the world. Loud pings bounce between the sub and the Keldysh every few seconds—exactly the clichéd pinging you would expect to hear while sitting in a submersible but a little higher in pitch and shorter in duration. Every so often, words trickle through the speaker: a sentence or two of Russian, significantly broken up by its journey through the water. For me, with my limited Russian vocabulary, the foreign patter and pings made the environment feel even more alien.

As we sank, I pressed my face up against the porthole and wrapped my head in a towel, trying to prevent light from inside the sub from contaminating my view outside. This part was familiar to me—astronomers gazing at the night sky are always protective of their night vision. The better adapted you are to the dark, the more stars you can see in the night sky.

Here, however, I was scouring the depths for a glimpse of bioluminescence from the host of bizarre creatures that populate our ocean’s depths and that give off pulses of light as they, or things around them, move. The plummeting submersible created a shock wave of bioluminescence radiating away from us. Creatures large and small, from jellyfish to microbes, flashed. It was a sight I’ll never forget, and it’s one that I treasured on each of my nine dives. I got into the habit of donning earphones, pairing the biological fireworks with the music of Radiohead and Pink Floyd. I half-expected to find those bands playing on the ocean floor.

So far, this dive, my first, had been very successful. After some initial exploration of the seafloor, we managed to track down a site rich with hydrothermal vents. For hours we cruised over the flanks of Menez Gwen and collected samples with the robotic arm from the gushing superheated vents. Microbes, mussels, and fish feasted on the bounty of these chemical oases.

Finding this spot on the bottom of the ocean may not seem like a big achievement, but it really was. All of those mapping luxuries that we employ on the surface of the Earth are useless in the ocean. The wavelengths we use for GPS navigation barely penetrate beyond a few millimeters into the ocean’s surface. In fact, the ocean is a bad place for transmitting just about any wavelength in the electromagnetic spectrum. Water—the key ingredient to life as we know it—turns out to be very good at hiding much of our own planet from us. Liquid water readily absorbs light, from short to long wavelengths, and thus we can’t “see” or communicate from the bottom of the ocean. This simple fact has confounded engineers for decades: no electronic mode of navigation or communication works underwater—no cell phones, no Wi-Fi, no GPS, no AM, no FM, no ham (amateur) radio, nothing.

Nothing makes it through the ocean over very long distances, except sound. This is partly why whales and dolphins use sound to comm...