There’s Lowell and the canals on his spiderweb maps. When he made them, he could not have known the findings of modern ophthalmology, which suggest that humans peering into the dark may catch glimpses of the faint shadows of tiny retinal veins within their own eyes. For decades, we tried so hard to make sense of those “little gossamer filaments” cobwebbing the face of Mars. Might it have been that we couldn’t escape our own ghostly image?
There’s a topographic map of the Asgard Range in Antarctica, a place I’ve flown over more than a dozen times, skimming the peaks in a Bell or AStar helicopter. Half a century has passed, and I’m still doing the same research as Wolf Vishniac, trying to detect life in one of the planet’s most impossible places. Next to the map is a paper by his wife, Helen, filled with descriptions of the cells of Cryptococcus vishniacii—cream-colored, nonfermentive, psychrophilic, “undescribed, imperfect yeasts.” Helen went on to publish numerous journal articles about her husband’s cultures. She tended to the slides for decades after his death, carrying those small slips of glass with her wherever she moved, from lab to lab, until she entered assisted living a couple of years ago.
And, of course, there is a copy of Elements, that crowning achievement, that bygone idea. The edition I couldn’t resist buying—one of the thousand editions printed since the invention of the printing press—happened to have one of the great paintings of the Romantic Era silkscreened on its cover. All the mathematics is bound by the portrait of a person standing on a precipice, caught in the wind, at once towering over the clouds and at the same time swallowed by nothingness.
This box contains the “traces of human events” that Herodotus spoke of. This is my “gift of the river.” We’ve been wrong about many things in the search for life. It’s been so hard to find an anchor, and so hard to know when our theories will no longer hold. The box reminds me of all who have come before me and what they’ve contributed.
It also reminds me of what is left to do. Mars, after all, is only our first step into the vast, dark night. New technologies are paving the way for life detection missions to the far reaches of our solar system, to the moons of the outer planets, far from what we once considered the “habitable zone.” To worlds that hold stacks of oceans amidst shells of ice, floating like a layer cake. That spew out jets of briny water through cryovolcanoes. That have pale hills and dark rivers and hydrocarbon rain. And then there are also the planets around other stars. There could be as many as forty billion planets that could support life in the Milky Way alone, belted with moons and moonlets—potentially an entire solar system for every person on Earth. The idea of knowing these places intimately, of one day touching their surfaces, may seem ludicrous. The universe has a speed limit—it’s slow, and these worlds are very far away. What could we ever know about them, besides a few details about their orbits, perhaps some spectrographic measurements of their atmospheres? They are points of light and shadow at the very edge of our sight, far beyond our grasp. Then again, that is exactly how Mars seemed only a century ago.
* * *
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AS MUCH AS Mars feels like a place we understand, a place like Earth, it is still the alien other. One of my favorite things inside the box, tucked in a bent folder, is a set of pictures that Opportunity took in 2010. All those years ago, it seemed like such a marvel that the rover was still working. No one would have dared to believe it would have thousands more sols of science. The dust was building, the power dropping. It had been traversing the planet for six years and was already long past its ninety-day expiration date. But then a gust of wind whistled across Meridiani Planum and cleaned some of the fine particles off the solar panels. With the unexpected spike in electricity output, the team commanded the panoramic camera to take a series of pictures that could be strung together with time-lapse photography.
The flickering images captured by the rover are unforgettable. There, on an ancient plain near the equator of Mars, against an ochre sky on a dusty day, the sun is setting. A white circle of light is drifting down over the dark desert. The terrain is bare, and the sky is still in the half-light of dusk. And on the horizon, with the dust having scattered all the red light away, the sunset glows an eerie, baffling, incandescent blue.
The color makes no sense. It rattles the mind. It rips at the seams of the physical world. Scientifically, I understand it—the properties of the light, the microphysics of the system. There is no mystery to behold. And yet the mystery, like many others in our universe, is profound, nearly incomprehensible. That blue. So recognizable, yet so foreign. Shining in a halo around our shared star, calling us like a siren.
For Emily
THIS IS A book about the search for life: life beyond our planet and, implicitly, a life beyond the one we live now. I have always been quick to recognize the hubris and ambition in hoping to play a role, however small, in such a pivotal breakthrough, and making it a cornerstone of my work. At times, I’ve worried that this kind of seeking has come with a consequence—a sense of restlessness, an inability to be content.
Not long after I finished this manuscript, the value of the life I have now, the one right here on Earth, tucked into a cozy spot in Washington, D.C., with my husband and family, was illuminated by a medical accident that pushed me to the brink of death. I landed in an ICU on life support, with a line in my neck, a ventilator in my throat, and my mother and husband by my side. As I lay dying, a series of fourteen transfusions replaced every drop of blood in my body, allowing me to live. This book could not possibly conclude without acknowledging the fourteen anonymous people who walked into donation centers, let strangers sink needles into their arms, and then walked back into the bright day. Because of them, I have my life back, this precious life here on Earth, and I have bright days ahead.
I also feel unspeakable gratitude toward those who have gathered around me during this dark time. They include my oldest, dearest friends: Lisha and Emma and Lippy and Kayje, who traveled hundreds of miles to ease my pain, to direct my medical care, and to keep me alive, in more ways than one, and Heather, Chelsea, Ying and Ryan, Jason and Meagan, Christine, Katherine, Erin, Shayna, Maya, Stephen, Leslie, Tisha, Tessa, Maria, Antje, Sherry, Nikki, Sarah, Angus, Hannah, Lawrence and Christina, Richard and Jeannie, Meghan and Nate, Ross and Kayte, Maxine and Joel, Jacob and Patti, Ajay and Amanda, Emma and Eric, Jeff and Laura, Alan and Annie, David and Ashley, and Judy and Mike. I’m also deeply grateful for the compassionate support I received from Georgetown University and countless wonderful colleagues there, and, of course, my lab. Even at the low points, they were never far from my mind. This was not the first time I have been surrounded and lifted by my students and postdocs, and I know it will not be the last.
I write a lot in this book about time and scale: about how we negotiate the dissonance between geologic timescales on the one hand, and human ones on the other; about how we live out our small, shining moments as human beings on this planet, hurtling through our enormous universe. I have been blessed that my shining moment, from the day I was born, has been shared with my family in Kentucky. Although it could have been no other way, I am so thankful I was born to Kate and John, the most compelling people I’ve ever known. What a joy it has been to be their daughter. (And what regret I feel that my mother does not appear in this book as much as she should!) In equal measure, I could not have become the person I became without my sister, Emily—my sister darling—who brought a distilled and pure happiness into my life and in so doing, taught me the meaning of unconditional love.
I also want to thank the many grandparents and aunts and uncles and cousins who have shaped me in immeasurable ways, and I want to thank my treasured children. For the longest time, they thought there would be just one copy of this book, and it would sit on the shelf of their shared room. In a sense they were right, because these words are and will always be for them. And most profoundly, I want to thank my husband, John, whose capacious mind shines througho
ut this book. He read and improved every passage, just as he has improved every part of me. He has given me the big, full life I always dreamed of. I told him at our wedding that he knew my heart, and he does. It still takes my breath away that we get to explore the expanses together.
This project began simply as a collection of thoughts that would never find expression on the pages of scientific journals. It would never have become a book without Christina, who decided to publish my first nonfiction essay, remains my favorite reader, and was convinced, long before I was, that this kind of writing might interest others. The book also wouldn’t have existed without sweet Matt, who, with help from Kristin, made sure I stayed in academia at the peak of my self-doubt and also introduced me to my literary agent, Jill. With her brilliant insights, Jill shaped a mess of ideas into something full of possibility, and together with Matt, led me to my editor, Amanda, who took my hand on a cold day in December and promised me it would work. She never let go. Amanda taught me everything about how to write a book. Without her help, it never would have been worthy of being printed.
Others who have supported me in this unlikely endeavor include my irreplaceable friend Dan, with his hundred years of wisdom, and Alan, with his stirring sense of the universe, as well as Kate, Tony, the Banff Centre, the Society of Fellows and the endless number of friends I made there, Marthe and Veronica and Jane for the kindness they bestowed on my children, Margaret for her interminable faith in me, the Massachusetts Cultural Council, MIT’s STS Department, and the Ellen Meloy Fund and their incredible board. I am profoundly thankful for my NASA colleagues—especially Paul, Heather, Bethany, Jim, John, Melissa, Stephanie, Will, Amy and Amy, Charles, Christine, Cherie, Jen and Jen, Doug, Steelie, and others on the SAM team, Alex, Haley, Morgan, Kevin, Abby, Steve, Jack, Kate, Jamie, Chris, Eric, Andy, Lee, Mary Beth, Jen, Dale, Tori, Brit, Joe, Paul, Lindsay, and Mary—to the early Mars mission scientists and engineers—Norm, John, Ben, Larry, and Gentry—and to my unsurpassed mentors—Maria, Ray and Eloise, Rick, Jim, Steve, John, Shere, Lindy, Pete, Gary, Scott, Dave, Roger, Kathy, Barb, Charles, Eske, Mark, and Roz. I am deeply grateful to Bill, who enhanced the manuscript tremendously with his historical depth, and Parker, who meticulously fact-checked each line, as well as Zach, James, Julie, Owen, Anita, Katie, Anne Cat, Maya, and Matt, and the staff of the Caltech, Harvard, MIT, Oxford, and JPL archives, the NASA History Office, and the Library of Congress, who all helped in various ways with research. In addition, I will always be indebted to those who read the leaden text of my early drafts—dearest Liz and Greg, Dedi, Maura and Heidi, and of course Deirdre, who is not only one of my closest friends, but also the reason I found and fell in love with John. I apologize to anyone I’ve inadvertently omitted, and also to those who have helped me in ways I’m not even aware of.
Eudora Welty once wrote about how things are often too indefinite to be recognized for themselves, to connect into a larger shape, until you are almost close enough to grasp them. But then “suddenly a light is thrown back, as when your train makes a curve, showing that there has been a mountain of meaning rising behind you on the way you’ve come, is rising there still.” In writing this book, I’ve come to understand better the meaning I find in searching for life. I’ve also come to appreciate all the people who came down this path before me and the astonishing lives they led, as well as the remarkable colleagues with whom I have the privilege of working today. In my final acknowledgments, I wish to extend my gratitude to all of those people, throughout the generations and across the disciplines, who have created and continue to deepen this field. If we find life on Mars, we will have done it together. In the meantime, we have this great human project, and we have one another.
Prologue
WORLD’S OLDEST ROCKS J. R. De Laeter, I. R. Fletcher, K. J. R. Rosman, et al., “Early Archaean Gneisses from the Yilgarn Block, Western Australia,” Nature, 292 (1981), pp. 322–324; D. R. Mole, M. L. Fiorentini, N. Thébaud, et al., “Archean Komatiite Volcanism Controlled by the Evolution of Early Continents,” Proceedings of the National Academy of Sciences, 111 (June 2014).
CORROSIVE AS BATTERY ACID The pH levels in these unique acid salt lakes, which have been studied for years as a Mars analog because of the pioneering work of West Virginia University Professor Kathy Benison, have been recorded to fall as low as 1.6. For more about the lakes and their extreme geochemical conditions, see: K. C. Benison and D. A. LaClair, “Modern and Ancient Extremely Acid Saline Deposits: Terrestrial Analogs for Martian Environments?” Astrobiology, 3, no. 3 (2003), pp. 609–618; B. B. Bowen and K. C. Benison, “Geochemical Characteristics of Naturally Acid and Alkaline Saline Lakes in Southern Western Australia,” Applied Geochemistry, 24 (2009), pp. 268–284; S. S. Johnson, M. G. Chevrette, B. L. Ehlmann, and K. C. Benison, “Insights from the Metagenome of an Acid Salt Lake: The Role of Biology in an Extreme Depositional Environment,” PLOS One, 10 (April 2015).
HOPING TO SIGNAL MARS Hans Zappe, Fundamentals of Micro-Optics, 1st ed. (Cambridge University Press, 2010), p. 298; Louise Leonard, Percival Lowell, An Afterglow (Boston: Richard G. Badger, 1921).
NO LAKES There are no longer any traditional lakes (i.e., lakes on the surface on Mars), but in 2018, the MARSIS Instrument on the European Space Agency’s Mars Express orbiter found intriguing evidence of a twenty-kilometer-wide subglacial lake deep under the south polar layered deposits. See: R. Orosei, S. E. Lauro, E. Pettinelli, et al., “Radar Evidence of Subglacial Liquid Water on Mars,” Science, 3 (Aug. 2018), pp. 490–493.
NO PLATE TECTONICS Many modelers agree that even an early epoch of plate tectonics on Mars is difficult to reconcile with the evidence for early crust formation and magnetic-field generation, though it has been suggested that Valles Marineris could be a plate boundary. See: D. Breuer and T. Spohn, “Early Plate Tectonics Versus Single-Plate Tectonics on Mars: Evidence from Magnetic Field History and Crust Evolution,” Journal of Geophysical Research: Planets, 108, no. E7 (2003); An Yin, “Structural Analysis of the Valles Marineris Fault Zone: Possible Evidence for Large-Scale Strike-Slip Faulting on Mars,” Lithosphere, 4, no. 4 (2012), pp. 286–330.
NO MAGNETIC FIELD Most estimates suggest that a global magnetic field of appreciable magnitude dissipated around four billion years ago. See: David J. Stevenson, “Mars’ Core and Magnetism,” Nature, 412, no. 6843 (2001), p. 214; Sean C. Solomon, Oded Aharonson, Jonathan M. Aurnou, W. Bruce Banerdt, Michael H. Carr, Andrew J. Dombard, Herbert V. Frey, et al., “New Perspectives on Ancient Mars,” Science, 307, no. 5713 (2005), pp. 1214–1220; and J. E. P. Connerney, J. Espley, P. Lawton, S. Murphy, J. Odom, R. Oliversen, and D. Sheppard, “The MAVEN Magnetic Field Investigation,” Space Science Reviews, 195, no. 1–4 (2015), pp. 257–291.
MUCH MORE LIKE EARTH Mars’s diameter is a bit more than half as large as Earth’s; in comparison, you would need more than eleven Earths side by side to match the diameter of Jupiter.
LIFTED GREENHOUSE GASES See: R. M. Haberle, “Early Mars Climate Models,” Journal of Geophysical Research, 103 (Nov. 1998), pp. 28,467–28,479; I. Halevy, M. T. Zuber, and D. P. Schrag. “A Sulfur Dioxide Climate Feedback on Early Mars,” Science 318, no. 5858 (2007), pp. 1903–1907; S. S. Johnson, M. A. Mischna, T. L. Grove, and M. T. Zuber, “Sulfur-Induced Greenhouse Warming on Early Mars,” Journal of Geophysical Research: Planets, 113, no. E8 (2008); R. M. Ramirez, et al., “Warming Early Mars with CO2 and H2,” Nature Geoscience, 7 (2014), pp. 59–63; and R. D. Wordsworth, “The Climate of Early Mars,” Annual Review of Earth and Planetary Sciences, 44 (2016), pp. 381–408.
WARM AND WET, AT LEAST PERIODICALLY See: R. A. Craddock and A. D. Howard, “The Case for Rainfall on a Warm, Wet Early Mars,” Journal of Geophysical Research Planets, 107 (Nov. 2002), pp. 21–36; S. W. Squyres and J. F. Kasting, “Early Mars: How Warm and How Wet?” Science, 265 (Aug. 1994); R. D. Wordsworth, et al., “Comparison of ‘Warm and Wet’ and ‘Cold and Icy’ Scenarios for Early Mars in a 3-D Climate
Model,” Journal of Geophysical Research Planets, 120 (June 2015), pp. 1,201–1,219; M. C. Palucis, et al., “Sequence and Relative Timing of Large Lakes in Gale Crater (Mars) after the Formation of Mount Sharp,” Journal of Geophysical Research: Planets, 121, no. 3 (2016), pp. 472–496.
“WARM LITTLE PONDS” Charles Darwin, letter to J. D. Hooker, February 1, 1871, Darwin Correspondence Project. In the letter to Charles Hooker, Darwin wrote: “But if (and oh what a big if) we could conceive” of the origin of life “in some warm little pond…” His instincts may have been right. Two leading possibilities today for the locus of the origin of life on Earth are hydrothermal vents deep in the ocean and freshwater pools within geothermal fields, similar to those in Yellowstone National Park. The latter has come to prominence in recent years for several reasons. The chemical composition of cells more closely resembles the chemical composition of pooling water within geothermal fields than that of deep-sea waters; organic molecules—the building blocks of life—could have accumulated in ponds more easily than in the deep ocean, and lower salt concentrations could have provided a more conducive environment for the first fatty-acid membranes to form. In addition, recent work now suggests that repeated cycles of wetting and drying may have been necessary to pattern the precursors of repeating informational molecules in membranous vesicles. If land is indeed required for life, at least life as we know it, Mars may hold more possibility than the icy moons of Jupiter and Saturn. See: Armen Y. Mulkidjanian, et al., “Origin of First Cells at Terrestrial, Anoxic Geothermal Fields,” Proceedings of the National Academy of Sciences, 109 (2012), pp. E821–E830; D. Deamer and B. Deamer, “Can Life Begin on Enceladus? A Perspective from Hydrothermal Chemistry,” Astrobiology (Sept. 2017), pp. 834–839; D. Deamer, First Life: Discovering the Connections between Stars, Cells, and How Life Began (Berkeley: University of California Press, 2011).
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