EUCLID’S ELEMENTS Euclid, Euclid’s Elements: All Thirteen Books Complete in One Volume: The Thomas L. Heath Translation (Santa Fe, N.M.: Green Lion Press, 2002).
PERFECT NUMBERS A perfect number is any positive integer that is equal to the sum of its proper divisors; for example, 6 is the sum of 1, 2, and 3 and 28 is the sum of 1, 2, 4, 7, and 14.
KANTIAN IDEAL Immanuel Kant, Critique of Pure Reason, trans. and ed. by Paul Guyer and Allen W. Wood (Cambridge University Press: 1998).
CARL FRIEDRICH GAUSS Gauss, who had an avid interest in extraterrestrials, is also the German rumored to have proposed the Pythagorean right triangle extraterrestrial-signaling scheme; whether or not the idea originated with him is not certain. Michael J. Crowe, The Extraterrestrial Life Debate, 1750–1900 (Mineola, N.Y.: Dover Publications, 2011), p. 205.
THE PARALLEL POSTULATE Euclid’s fifth postulate is: “If a straight line intersects two other straight lines, and so makes the two interior angles on one side of it together less than two right angles, then the other straight lines will meet at a point if extended far enough on the side on which the angles are less than two right angles.” Euclid, Euclid’s Elements: All Thirteen Books Complete in One Volume: The Thomas L. Heath Translation.
AVOIDED USING IT J. J. O’Connor and E. F. Robertson, “Non-Euclidean Geometry,” JOC/EFR (Feb. 1996).
KEPT HIS DOUBTS A SECRET Ibid.
THEORY OF GENERAL RELATIVITY Albert Einstein, “Der Feldgleichungen der Gravitation,” Königlich Preußische Akademie der Wissenschaften (1915), pp. 844–847.
PHOTOSYNTHESIS EVOLVED LATE Joseph R. Michalski, Tullis C. Onstott, Stephen J. Mojzsis, John Mustard, Queenie H. S. Chan, Paul B. Niles, and Sarah Stewart Johnson, “The Martian Subsurface as a Potential Window into the Origin of Life,” Nature Geoscience, 11, no. 1 (2018), p. 21; Tanai Cardona, James W. Murray, and A. William Rutherford, “Origin and Evolution of Water Oxidation before the Last Common Ancestor of the Cyanobacteria,” Molecular Biology and Evolution, 32, no. 5 (2015), pp. 1,310–1,328; Akiko Tomitani, et al., “The Evolutionary Diversification of Cyanobacteria: Molecular-Phylogenetic and Paleontological Perspectives,” PNAS, 103, no. 14 (2006), pp. 5,442–5,447.
THE VAST MAJORITY OF MICROBES Yinon M. Bar-On, Rob Phillips, and Ron Milo, “The Biomass Distribution on Earth,” Proceedings of the National Academy of Sciences, 115, no. 25 (2018), pp. 6,506–6,511.
DEEPEST SUBTERRANEAN MINES B. Lollar Sherwood, Georges Lacrampe-Couloume, G. F. Slater, J. Ward, Duane P. Moser, T. M. Gihring, L-H. Lin, and Tullis C. Onstott, “Unravelling Abiogenic and Biogenic Sources of Methane in the Earth’s Deep Subsurface,” Chemical Geology, 226, no. 3–4 (2006), pp. 328–339; Katrina J. Edwards, Keir Becker, and Frederick Colwell, “The Deep, Dark Energy Biosphere: Intraterrestrial Life on Earth,” Annual Review of Earth and Planetary Sciences, 40 (2012), pp. 551–568; Cara Magnabosco, Kathleen Ryan, Maggie C. Y. Lau, Olukayode Kuloyo, Barbara Sherwood Lollar, Thomas L. Kieft, Esta Van HeerDen, and Tullis C. Onstott, “A Metagenomic Window into Carbon Metabolism at 3 km Depth in Precambrian Continental Crust,” The ISME Journal, 10, no. 3 (2016), p. 730.
MORE OF THOSE LITTLE HOMES Joseph R. Michalski, et al.,“The Martian Subsurface as a Potential Window into the Origin of Life,” Nature Geoscience.
STARTING TO UNDERSTAND T. C. Onstott, B. L. Ehlmann, H. Sapers, M. Coleman, M. Ivarsson, J. J. Marlow, A. Neubeck, and P. Niles, “Paleo-Rock-Hosted Life on Earth and the Search on Mars: A Review and Strategy for Exploration,” Astrobiology (2019).
SITE CALLED MIDWAY Paul Voosen, “NASA’s Next Mars Rover Aims to Explore Two Promising Sites.” Science 362, no. 6411 (2018), pp. 139–140. Midway’s strongest advocate in the landing site selection process was trailblazing Caltech professor Bethany Ehlmann, who has published extensively on Northeast Syrtis and has spearheaded a charge to explore ancient subsurface terrains.
RIDGES AND MESAS J. Mustard, et al., “Mars 2020 Candidate Landing Site Data Sheet: NE Syrtis,” NASA JPL.
“LIFE AS WE DON’T KNOW IT” This research area is focus of the Laboratory for Agnostic Biosignatures (LAB) Project, for which I serve as Principal Investigator. With support from NASA’s Astrobiology Program, LAB aims to develop life detection methods that identify unknowable, unfamiliar features and chemistries that may represent processes of life as-yet unrecognized. The LAB team includes biologists, chemists, computer scientists, mathematicians, and instrument engineers. Building on seminal work in the astrobiology community (i.e., P. G. Conrad and K. H. Nealson, “A Non-Earthcentric Approach to Life Detection,” Astrobiology, 1, no. 1 (2001), pp. 15–24), we are also designing tools for detecting these signatures and strategies for interpreting them (www.agnosticbiosignatures.com [inactive]).
CHEMICAL COMPLEXITY S. M. Marshall, A.R.G. Murray, and L. Cronin, “A Probabilistic Framework for Identifying Biosignatures Using Pathway Complexity,” Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 375, no. 2109 (2017), p. 20,160,342; S. S. Johnson, E. V. Anslyn, H. V. Graham, P. R. Mahaffy, and A. D. Ellington, “Fingerprinting Non-Terran Biosignatures,” Astrobiology, 18, no. 7 (2018), pp. 915–922.
DIFFERENT MOLECULAR FOUNDATION For instance, life might have evolved to use cosmic rays as a source of energy, just as we use visible wavelengths of light here on Earth, or to use sulfur, silicon, or ammonia in lieu of carbon as the building block of life. J. E. Lovelock, “A Physical Basis for Life Detection Experiments,” Nature, 207, no. 997 (1965), pp. 568–570; P. H. Rampelotto. “The search for life on other planets: Sulfur-based, silicon-based, ammonia-based life,” Journal of Cosmology, 5 (2010), pp. 818–827.
A THING “UNCUTTABLE” Some later scholars, it should be noted, have interpreted Aristotle’s idea in Physics that there is a smallest size of material substrate on which it is possible for the form of a given natural tissue to occur (e.g., bone or blood) as evidence that Aristotle believed in the existence of minimal physical parts. See: Sylvia Berryman, “Ancient Atomism,” in The Stanford Encyclopedia of Philosophy, Edward N. Zalta, ed. (Winter 2016 edition); “Scholastic Philosophy and Renaissance Magic in the De Vita of Marsilio Ficino,” Renaissance Quarterly, 37 (1984), pp. 523–554; Ruth Glasner, “Ibn Rushd’s Theory of Minima Naturalia,” Arabic Sciences and Philosophy, 11 (2001), pp. 9–26; John E. Murdoch, “The Medieval and Renaissance Tradition of Minima Naturalia,” in Christoph Lüthy, John E. Murdoch and William R. Newman, eds., Late Medieval and Early Modern Corpuscular Matter Theories (Leiden: Brill, 2001, pp. 91–132).
NOT BUILT FROM INANIMATE PARTS For a fascinating discussion of worldviews, see the work of philosopher Lucas Mix, who discusses how Lucretius, an Epicurean atomist, viewed the world as fundamentally dead whereas Aristotle viewed the world as fundamentally alive, and “by and large Aristotle won for two thousand years.” Lucas John Mix, “The Meaning of ‘Life’: Astrobiology and Philosophy,” University of Washington Seminar Series, NASA Astrobiology Institute Virtual Planetary Lab, 12 May 2012, and Lucas John Mix, Life in Space: Astrobiology for Everyone (Cambridge: Harvard University Press, 2009), pp. 246–247; see also: Mohan Matthen and R. James Hankinson, “Aristotle’s Universe: Its Form and Matter,” Synthese, 96, no. 3 (1993), pp. 417–435.
THE HEAVENS Aristotle, “Book IV,” On the Heavens, trans. W. K. C. Guthrie (Cambridge: Harvard University Press, 1939).
MANY OF THEM WERE WRONG Alan Lightman, Searching for Stars on an Island in Maine (New York: Pantheon Books, 2018), p. 145; Armand Marie Leroi, “6 Things Aristotle Got Wrong,” Huffington Post (Dec. 2, 2014).
PARADIGM HAD SHIFTED In the 1960s, Thomas Kuhn proposed the idea of paradigm shifts in science: the idea that a dominant mode of scientific thought slowly accumulates errors, then dominant thinking radically shifts to a new paradigm. T. S. Kuhn, The Structure of Scientific Revolutions (Chicago and London: University of Chicago Press, 1962).
MECHAN
ICAL, CLOCK-LIKE UNIVERSE “Newtonian Cosmology and Religion,” Cosmic Journey: A History of Scientific Cosmology (American Institute of Physics).
“IF THE DOORS OF PERCEPTION” William Blake, “The Marriage of Heaven and Hell,” in The Poetical Works, ed. John Sampson (Oxford University Press, 1908; Bartleby.com, 2011), lines 115–116. Similarly, Einstein once said, “We are in the position of a little child entering a huge library filled with books in many languages. The child knows that someone must have written those books. It does not know how. It does not understand the languages in which they are written. The child dimly suspects a mysterious order in the arrangements of the books but doesn’t know what it is. We see the universe marvelously arranged and obeying certain laws but only dimly understand those laws.” Quoted in Alan Lightman, Searching for Stars on an Island in Maine (New York: Pantheon Books, 2018), pp. 115–116.
MEDIEVAL EARTHQUAKES Allison McNearney, “The Buried Secrets of the World’s Very First Lighthouse,” The Daily Beast (Oct. 21, 2017).
THE MECHANICAL BIRDS James Crawford, “The Life and Death of the Library of Alexandria,” LitHub (March 13, 2017).
PARTICLES AND FORCES For a beautiful meditation on a scientist’s belief in the material world, see: Alan Lightman, Searching for Stars on an Island in Maine (New York: Pantheon Books, 2018).
RIVETING LETTERS Papers of William Henry Pickering, 1870–1907 (Harvard University Archives, HUG 1691).
INTERLEAVED ARE HUNDREDS Ibid.
SILENT-FILM FOOTAGE “Hallo, Mars? Mr. Marconi and his new aerial on the radial yacht ‘Elettra,’ with which he hopes to call up Mars,” British Pathé.
A PICTURE FROM AROUND 1910 David Peck Todd papers, 1862–1939 (inclusive), Yale University Manuscripts & Archives.
WORLD IS GETTING QUIETER Duncan H. Forgan and Robert C. Nichol, “A Failure of Serendipity: The Square Kilometre Array Will Struggle to Eavesdrop on Human-like Extraterrestrial Intelligence,” International Journal of Astrobiology, 10, no. 2 (2011), pp. 77–81.
WITHIN THEIR OWN EYES Lowell observed linear features not only on Mars but also Mercury (“cracks”), the moons of Jupiter (“lineaments”), and Venus (“spokes”). The similarities between the “spokes” he charted on a map of the surface of Venus at the turn of the twentieth century and a modern image of blood vessels diverging from the optic cup are uncanny; see: W. Sheehan and T. Dobbins, “The Spokes of Venus: An Illusion Explained,” Journal for the History of Astronomy, vol. 34, part 1, no. 114 (2003), p. 61.
“LITTLE GOSSAMER FILAMENTS” Percival Lowell, Mars as the Abode of Life (New York: The Macmillan Company, 1908), p. 146.
“UNDESCRIBED, IMPERFECT YEASTS” Helen S. Vishniac and Walter P. Hempfling, “Cryptococcus Vishniacii sp. nov., an Antarctic Yeast,” International Journal of Systematic and Evolutionary Microbiology, 29, no. 2 (1979), pp. 153–158.
TENDED TO THE SLIDES Ephraim Vishniac, phone interview by Sarah Johnson (Sept. 8, 2017).
THE EDITION Euclid, Euclid’s Elements: With Notes, an Appendix, and Exercises by Issac Todhunter (independently published, 2017). The painting is Caspar David Friedrich, Wanderer above the Sea of Fog, 1818, oil on canvas (2007).
“TRACES OF HUMAN EVENTS” Herodotus, quoted in Thomas Harrison, “Review: Herodotus,” The Classical Review, 49, no. 1 (1999), p. 16.
AS MANY AS FORTY BILLION Erik A. Petigura, Andrew W. Howard, and Geoffrey W. Marcy, “Prevalence of Earth-Size Planets Orbiting Sun-like Stars,” Proceedings of the National Academy of Sciences, 110, no. 48 (2013), pp. 19,273–19,278; Melissa Block, “Study Says 40 Billion Planets in Our Galaxy Could Support Life,” NPR, All Things Considered (Nov. 5, 2013).
SPEED LIMIT For an illuminating discussion of limits in science, from the speed of light as the speed limit of the universe to the limits Heisenberg uncovered about what can be measured with certainty, see: John D. Barrow, Impossibility (Oxford University Press, 1998).
ACROSS MERIDIANI PLANUM The sunset images were collected on November 4 and 5, 2010. Guy Webster, “Martian Dust Devil Whirls Into Opportunity’s View,” NASA (July 28, 2010); Webster, “Mars Movie: I’m Dreaming of a Blue Sunset,” NASA (December 22, 2010).
THE MICROPHYSICS OF THE SYSTEM On Earth, blue light is scattered more efficiently than red light, which has a longer wavelength. This phenomenon, Rayleigh scattering, results from light scattering in all directions off of objects that are much smaller than the wavelength of light, in this case the very small molecules of air in our atmosphere. This is why our sky is blue. But by the time incident light from the sun has traveled through a great deal of atmosphere (e.g., at sunset, when the sun is low on the horizon), the blue light has been mostly scattered away. The result is that mostly red and yellow photons hit our eyes. On Mars, there is very little air, so Rayleigh scattering is less prominent. Most of the light is scattered by dust particles, which tend to be similar in size or larger than the wavelengths of incident light. As the light is scattered, the blue wavelengths are deflected less than red wavelengths, and sunsets on Mars appear blue. Recent observations from the Compact Reconnaissance Imaging Spectrometer aboard the Mars Reconnaissance Orbiter have led to important advances in characterizing the scattering properties of Martian aerosols; see: M. J. Wolff, M. D. Smith, R. T. Clancy, R. Arvidson, M. Kahre, F. Seelos, S. Murchie, and Hannu Savijärvi, “Wavelength dependence of dust aerosol single scattering albedo as observed by the Compact Reconnaissance Imaging Spectrometer,” Journal of Geophysical Research: Planets 114, no. E2 (2009).
ABOUT THE AUTHOR
SARAH STEWART JOHNSON is an assistant professor of planetary science at Georgetown University. A former Rhodes Scholar and White House Fellow, she received her PhD from MIT and has worked on NASA’s Spirit, Opportunity, and Curiosity rovers. She is also a visiting scientist with the Planetary Environments Lab at NASA’s Goddard Space Flight Center.
1. In the prologue of The Sirens of Mars, the author writes, “The story of Mars is also a story about Earth: how we’ve sought another stirring of life in the universe, and what that search has come to mean….Mars has been a blank canvas. And tenderly, our human seeking has rushed to fill it.” How does the story of Mars and Mars exploration reflect the story of Earth? Do you think Mars is still a “blank canvas” today? Why or why not?
2. Throughout the book, the author weaves in stories from her own life, painting an image of a young girl, and later a young woman, perennially intrigued by the same thing: space, the stars, and Mars. Why do you think this was so arresting to her, even as a child? Have you had a similar guiding star in your life, something you constantly turn to with wonder and awe?
3. The Mariner 4 mission was focused on gathering images of Mars that would be far more powerful than the best telescopic observations of the time. The author writes, “Like Martin Luther insisting on a direct relationship with God, the imaging eliminated the need for an interpreter.” What do you think is gained, for scientists or the general public, in having this direct relationship with the planet?
4. Once the Mariner 4 transmitted its images of Mars, it revealed that the surface of the planet was covered in craters—indicating that Mars was likely “dead.” The media and the world reacted in disappointment. “Upon seeing the pictures, Lyndon Johnson sighed, ‘It may be—it may just be—that life as we know it…is more unique than many have thought.’ ” Why do you think it was so disappointing to learn that there was no life currently on Mars? What does the idea of life being “unique” to Earth invoke in you?
5. The author frequently describes her relationship with her career and her craft via religious metaphor, explaining that it felt “holy” to be present in Mission Control at NASA’s Jet Propulsion Lab or writing how it feels to worship her scientific pursuits. Why do you think the author uses religion to describe her passion?
6. Discuss the story of David McKay, the geologist who studied ALH84001 in the 1990s and determined th
at the slice of rock contained evidence of life on Mars. Only a year after publishing his groundbreaking study, his arguments had been largely abandoned by the scientific community and he found himself under immense stress. Consider the fact that any day, new evidence can be discovered that may entirely discredit a person’s work—or, as the author says: “The collapse of an abiding belief is always just one flight, one finding, one image, away.” How do you think scientists are able to cope with this ever-shifting landscape in their field? How would you cope in this kind of environment?
7. During the author’s sophomore year of college, she attended a presentation by MIT professor Maria Zuber. Partway through the talk, she realized that this was the first time she had heard another woman give a presentation on planetary science. Discuss what Dr. Zuber’s and the author’s experiences may be like, being women in such a male-dominated field. What factors might contribute to there being fewer women in fields like planetary science? What do you think the author’s colleagues could do to help ease some of the difficulties of being the sole woman, or one of the sole women, on the job? Is there anyone in your life in a similar situation?
8. The author mentions that Dr. Zuber was a major inspiration to her when she was a young student. Why do you think the author found Dr. Zuber to be inspiring? Do you have someone in your life that you can look up to like this? Why do you find them to be inspiring?
9. On a trip to Hawaii for a geoscience class in college, the author and her classmates visited a volcano. There she encountered a fern growing amongst the solid lava and she was utterly transfixed by the plant. She writes, “That fern on the volcano was even more striking up there by itself, all alone. It was just so impossibly triumphant….Huddled under a rock, growing against the odds, that fern stood for all of us.” Do you agree, that human beings are like that sole fern within a seemingly desolate landscape? Why or why not?
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