In ten billion years, the Sun will run out of hydrogen and burn out, swallowing the inner planets of our Solar System into the abyss of its collapse as the outer planets drift farther and farther. In time, the cosmos itself will run out of energy and none will be left to succor life — the fact of it or the possibility of it — as the universe goes one expanding into the austere emptiness of pure spacetime. So will end the short line of life in the ledger of eternity. In the meantime, we are here on our improbable planet, living our improbable lives — perishable triumphs against the immense cosmic odds of nonexistence, haunted by our earthly existential loneliness nested into our cosmic loneliness. Is it any wonder that, since we first looked up at the night sky, we have been yearning to find what Whitman called “beings who walk other spheres,” searching for life on other worlds that tells us something about how to live on this one, something about the deepest meaning of life itself?

Planetary scientist Sarah Stewart Johnson takes up these questions in The Sirens of Mars: Searching for Life on Another World (public library) — a sweeping civilizational memoir of our longing for cosmic companionship and the particular pull of the red planet on our imagination, rendered by our science into an affirmation of Ray Bradbury’s Mars-fomented insistence that it is part of our nature “to start with romance and build to a reality,” living proof of Richard Feynman’s passionate conviction that “nature has the greatest imagination of all.”

Reverencing the long arc of transmuting theory into truth, Johnson traces how we went from the illusory Martian “canals” of the early observers to the discovery of real water-lain sedimentary rocks by our space probes, how all the things we got wrong paved the way for the revelation of reality — a reminder, she observes, that “the truth can be a chimeric thing, the collapse of an abiding belief is always just one flight, one finding, one image, away.”

Across the centuries, this romance of reality is populated by some remarkable characters: We meet the naturalist and amateur astronomer who, convinced that Mars was an undiscovered wilderness and its canals were made of vegetation, strode into town in the middle of a World War on one of his two horses, Jupiter and Saturn, to cable his reports; the commodities broker turned adventurer who, after swimming the English Channel and climbing most of the world’s tallest mountains, grew bored of Earth and set out to observe Mars from a balloon, only to be swarmed in a savage thunderstorm, barely surviving his crash into the shark-infested Coral Sea; the woman who learned to grind telescope mirrors when she was ten, became the first in her family to go to college and the first in her high school to earn a doctorate, then transformed planetary cartography by devising an elaborate laser-based system for mapping the topography of Mars while rearing two small children.

Johnson’s own search for life on other worlds began by studying life in the most otherworldly regions of this one. Plumbing the Siberian permafrost for evidence of ancient bacteria, she finds herself holding cells twenty thousand times her own age. An epoch after Little Prince author Antoine de Saint-Exupéry contemplated the desert and the meaning of life while stranded in the Sahara, she pitches a small yellow tent in the eerie expanse between Death Valley and the Mojave Desert, reading Blake and Dostoyevsky and West with the Night like sacred texts, probing them for clues about the meaning of it all, about the nature and mystery of life. She reflects:

All I wanted was to find some solid points, some method to triangulate, some way to pattern a sense of human understanding onto the vast physical world around me, a world marked by human absence. Soon, though, I began to realize the Granite Mountains weren’t as intensely empty as they seemed. When I’d first gazed into the Mojave, everything seemed muted. All the color had been drained, sipped away by the parched air. The plants were a whitish khaki green, like fistfuls of dried herbs. I had the urge to spit on them, thinking it was the least I could do, a small act of kindness. But after a while, my senses started to adjust. The sagebrush began to look like splashes, almost like raindrops hitting a lake. I started to see the life all around me — in the spine-waisted ants and blister beetles, even in the dark varnish of the desert rocks, a sheen potentially linked to microscopic ecosystems… I had a visceral sense of the world popping from two dimensions into three, of seeing a landscape in a way I’d never viewed it before.

It is this yearning to understand the fundaments of life that drives Johnson toward the mystery of Mars. Still in her twenties, she becomes part of the historic Opportunity mission and watches in awe as the rover beams back the first images of the immense Endurance Crater’s walls — an unprecedented glimpse of “layers that had been stacked like the pages of a closed book, one moment in time pressed close against the next,” hinting at the planet’s history and at the possible future of our own world. She recalls:

Ours were the first human eyes to peer into that mysterious abyss, and it was one of the most breathtaking things I’d ever seen. As I stared into the center of the crater, I felt like Alice in Wonderland falling through a rabbit hole. “What is this world?” I thought, there on the verge of Endurance, my eyes wide. “What is this piercingly wild place?” The giant cavity was laced with hummocks of sand. The most ethereal gossamer dunes filled the void at its center, unlike any dunes I’d ever seen. They looked like egg whites whipped into soft pinnacles. And enveloping the edges, there was undulating outcrop, cut with gorgeous striations, deeper than I was tall.

In between peering into fractures, studying chemical gradients, and looking for evidence of subterranean aquifers, the search is laced with existential questions — questions Voltaire took up epochs ago in his visionary parable Micromégas, from which Johnson draws inspiration; question Carl Sagan and Ray Bradbury contemplated in their own reckoning with Mars. The most disquieting of them is the question of what life looks like in the first place — perhaps Martian life is of substance so alien and scale so discrepant that we might not even recognize it; perhaps it is composed of an entirely new biochemistry, built upon an entirely different molecular foundation, which we have neither the tools nor the minds to discern.

In a passage that echoes the sentiment at the heart of “When I Heard the Learn’d Astronomer” — Whitman’s timeless gauntlet at the limits of scientific knowledge — Johnson considers our creaturely blind spots:

We have human brains within human skulls, and we understand little of what surrounds us. The limits of our perception and knowledge are palpable, especially at the extremes, like when we’re exploring space. There is so little data to tell us who we are and where we are going, why we are here, and why there is something rather than nothing. This is the affliction of being human in a time of science: We spend our lives struggling to understand, when often we will have done well, peering out through those narrow chinks, just to apprehend.

Still, we go on searching, go on trying to understand, because the search itself shines a sidewise gleam on the ultimate questions pulsating beneath our touchingly human lives. Johnson writes:

We are unique and bounded, and we may well be in decline, for we know that species come and go. We are a finite tribe in a temporary world, marching toward our end.

And what of life itself? Must it be finite as well? What if life is a consequence of energetic systems? What if the nothing-to-something has happened time and again and, because the chinks in our cavern are so small, we don’t know it? For me, this is what the search for life amounts to. It is not just the search for the other, or for companionship. Nor is it just the search for knowledge. It is the search for infinity, the search for evidence that our capacious universe might hold life elsewhere, in a different place or at a different time or in a different form.

But perhaps loveliest of all is that tucked into her passionate search for life on another world is her passionate love letter to this one — a soulful reminder that while we are expending superhuman resources on searching for a mere microbe on Mars, we are living on a planet capable of trees and bioluminescence and Bach. It is on this world that she learns just how rare life is, and how possible. “Wherever life can grow, it will. It will sprout out, and do the best it can,” Gwendolyn Brooks wrote in one of her finest poems — a mirthful fact Johnson discovers while ascending the desolate summit of Hawaii’s Mauna Kea volcano:

As the road climbed, we passed the tree line, then the last of the scrub and the last of the lichens, until we were above even the clouds. The landscape was gray and red and black in every direction; in places it even smoldered with a sheen of purple. There were shards and ash and cinder cones. It felt like a bruise, crystallized in the world. One day, when everyone was having lunch, I wandered over to check out the view from a distant ridge, where the solid lava gave way to pyroclasts and tephra. Without really noticing, I was kicking at the rocks as I stepped. I overturned a surprisingly large one with the toe of my boot, and as my eyes fell to my feet, I startled. Beneath the vaulted side of that adamantine black rock, a tiny fern grew, its defiant green tendrils trembling in the air. There in the midst of all that shattered silence was a tiny splash of life. I crouched down to see it better.

[…]

It was just so impossibly triumphant. I couldn’t pull myself away; I looked at it for so long that the others had to come find me. I showed it to them, but I didn’t have the words to explain its beauty, its significance. I couldn’t tell them that somehow, huddled under a rock, growing against the odds, that fern stood for all of us.

The Sirens of Mars is a wondrous read in its entirety. Complement it with Annie Dillard — whom Johnson read in that desert tent — on our planetary destiny, then revisit this breathtaking animated poem from former U.S. Poet Laureate Tracy K. Smith’s collection Life on Mars.