Five Billion Years of Solitude

by Lee Billings

  A few audience members laughed again, this time with bitter cynicism. Politically, the country was hyperpolarized, and financially it was mired knee-deep in debt. To think that any U.S. politician, let alone the president, would choose to expend one shred of political capital pursuing a voyage to the stars against such heavy headwinds smacked of the same wishful thinking that had years ago tipped the TPF project into calamity.

  Moments later, Seager stood again before the crowd. She was scheduled to deliver a prepared talk but had discarded most of her presentation in light of the debate sparked by Charbonneau’s and Marcy’s remarks.

  “We want to go out and map the very nearest stars,” Seager reiterated, establishing the common ground on which everyone could agree. “Thousands of years from now, when people are embarking on their interstellar journey, they will look back and remember us as the people who found the planets like Earth around the very nearest stars. . . . I want to say I love NASA; NASA has helped my career tremendously. But I also see that NASA probably can’t do the Terrestrial Planet Finder within the next forty years. That has become more and more clear to me, and everybody in this room knows that I am one of the biggest, ardent supporters of any terrestrial planet–type mission. That’s what I want to do. I want a TPF in my lifetime. . . . And until now I never really worried about that.” For a fraction of a second, her gaze and voice betrayed a sudden hint of sadness.

  Seager noted that her position as a tenured MIT professor gave her tremendous security, which offered an opportunity—almost an obligation—to pursue high-risk, high-reward research. With flagging confidence that NASA could achieve TPF within her lifetime, she had been forced to consider other paths, new developments. One in particular looked promising: the recent debut of a new generation of commercial spaceflight providers, a select group of high-tech start-ups that were building rockets and spaceports with an eye toward at last overcoming the crippling paradigm of high launch costs. The companies had names such as SpaceX, Blue Origin, and XCOR, and multimillionaire CEOs who had made their fortunes with companies like PayPal, Amazon, and Intel. Seager thought the new companies might finally bring the profitable, sustainable human expansion into space that NASA had failed to deliver. They could be a powerful means to an elusive end, kicking off the next wave of synergies astronomers needed to lower the costs and accelerate the launches of TPF-style space telescopes, bringing the light of other living worlds into the lives and careers of all those assembled before her in the room. She had summoned her friends and colleagues to the meeting not only to discuss the field’s future, but also to bid it a temporary farewell. Her work on exoplanets would continue, but it would compete against a new, overarching emphasis on aiding the emergence of a self-sustaining commercial spaceflight industry. The surprise announcement set off whispering reverberations through the crowd.

  “That’s what I’m going to be doing now,” Seager explained with firm determination. “Most of you haven’t seen me at meetings lately; you won’t see me a lot in the future, because I’m investing in this. And if you see me working on asteroids and Mars, you’ll know that I’m not really interested in those that much. I’m interested in getting the commercial spaceflight world whatever I can to help them.” She cited estimates for launch costs: reaching orbit on one of NASA’s space shuttles had cost some $100 million, while a ride on a simpler Russian Soyuz rocket was only $10 million. Commercial providers could perhaps drop launch costs by another order of magnitude. “We need them to succeed if we want to do Terrestrial Planet Finder, because we’re never going to be able to do it at the ten-billion-dollar price tag. If we get that down by helping them, it will happen.”

  After Seager’s talk, the audience filed out of the auditorium into the hallway, clumping into loose pockets of caffeinated conversation. I listened as a biochemist explained to an astrophysicist how the quest for a life-finding space telescope resembled the race during the 1990s to sequence the human genome. “There were all these different groups with the technologies to do it just trashing each other,” said the biochemist. “Then you had the government agencies and the academic institutions and the pharmaceutical companies all separately decide to try to sequence it for their own ends. That mix of state and commercial competition pushed everyone toward the goal. . . . You guys need to figure out how to make China decide to go find the first habitable planets and name them all in Chinese.”

  Over by the coffee and tea tables, an engineer told a scientist that it would be straightforward to send a robotic probe at 10 percent of light-speed to Alpha Centauri: all he needed was a nuclear reactor from a Virginia-class submarine hooked up to a high-impulse electric propulsion system. “We could do it with today’s technology!” the engineer exclaimed. “We’d probably be alive to see the pictures it sent back!” The scientist’s only response was a polite nod, as if the engineer had forgotten to factor in a few important variables in his mental calculations.

  That evening, after the conference’s official end, a handful of the participants migrated from the Media Lab to Seager’s office on the seventeenth floor of MIT’s Building 54, the Green Building, the tallest high-rise in Cambridge. At Seager’s invitation, some of us climbed up to the rooftop, which was dotted with antennae and white radar domes, to gaze down at the twinkling lights of Boston’s skyline and at sailboats plying the calm waters of the Charles River. Mountain, Seager, and Grunsfeld chatted quietly, admiring the view. Traub stood silent for a time, watching the sunset. Marcy clambered up to pose for a few pictures beneath the immense radar dome, then descended. He mostly made small talk, but, when pressed, would dive again into discussing NASA’s plight.

  “NASA’s in big trouble,” he told me later. “It seems like even with all its infrastructure and expertise, it can’t outdo the private sector. It’s unable to overcome its own bureaucracy. How could NASA turn its back on TPF? I don’t want to blame NASA per se; maybe it’s not really NASA’s fault. Maybe it’s just that we have challenges when we try to organize ourselves to do great things. Rome falls. People are imperfect. We make incredibly tragic mistakes. . . . It’s just our nature, it seems.” He raised an empty hand, with thumb and forefinger angled like chopsticks grasping a single grain of rice. “We are just this far above the ants. That’s how I see it. We function in some ways like a bee colony. It’s natural. But, you know, there is something called colony collapse disorder, too.”

  Back inside the Green Building, the discussions continued, and a drift of people buzzed around Seager, the queen bee of this transitory hive. Standing at its fringes, I overheard her muse again about interstellar travel. “I don’t know if we’ll ever leave the solar system,” she said. “All I know is, it would be nice to have the option.”

  Into the Barren Lands

  An expanding shell of light surrounds our solar system, with our Sun as its source. The shell is not perfectly spherical, but instead tapered like an hourglass at its midsection, where some light is extinguished by thick lanes of gas and dust within the Milky Way’s spiraling galactic plane. Above and below the galactic plane, relatively free of occluding debris, the Sun’s photonic shell ripples outward in twin lobes, ever expanding at the speed of light. Though the shell’s boundaries sweep three hundred thousand kilometers farther away from us every second, their expansion through the great intergalactic voids is so glacial that their position can be pegged at 4.6 billion light-years away. The shell’s edges are composed of photons first erupted in the flash of thermonuclear ignition that announced our star’s birth. Each unfolding moment of our solar system’s history follows behind, encoded in planetary reflections, refractions, and occultations of starlight. In all probability, the beginning of the end for this photonic broadcast will occur some six billion years from now, when our Sun, long since swollen into a pulsating red giant, finally burns through its last stores of hydrogen and helium. It will leave behind scorched planets, an evanescent nebula of ionized gas, and a stellar remnant, a white-hot ember of carbon and oxygen ash. Sl
owly cooling over the eons, the remnant’s faint light will finally fade to black, switching off the solar transmission as surely as scissors cutting a thread, leaving only the light of ancient days to echo through eternity.

  Borne on photons, the echoes of primordial and Precambrian time—the formation of planets, the emergence of life on Earth, the oxygenation of our world’s atmosphere, the invasion of the land—all long ago left the Milky Way to wash over the surrounding galaxies, galactic clusters, and superclusters. An observer somewhere among the trillion stars of Andromeda, our nearest neighboring spiral, would today see the Earth of 2.5 million years ago, when the forerunners of Homo sapiens were perfecting the production of crude stone tools in sub-Saharan Africa. Seen from the Large Magellanic Cloud, a dwarf galaxy swooping near the Milky Way, our world would be locked in the glacial advance of 160,000 B.C., with our ancestors poised to migrate out of Africa as the ice sheets retreated. Within our own galaxy, the echoes are closer to home. Among the open clusters and blue hypergiant stars of the Carina Nebula, somewhere between 6,500 and 10,000 light-years away, the Earth appears as it was during the rise of agriculture and the Bronze Age civilizations of Mesopotamia, Egypt, and the Indus Valley. Light from the Earth of Thales, Democritus, and other ancient Greeks now washes over the blazing newborn stars and shimmering molecular clouds of the Christmas Tree Cluster, just over 2,500 light-years distant. The Earth in the skies of the giant planets circling the Sun-like star HR 8799 has just begun transmitting in radio and perfecting the internal combustion engine. The first television transmissions of the 1930s now roll over the ice-blue stars of Regulus, and news of 1969’s Apollo 11 lunar landing has just reached the aging yellow suns of Capella. Whether any of this has actually found an audience somewhere out there, we cannot yet say. For all we know, the lively broadcast from Earth may be the only one of its kind in the observable universe.

  Viewed from the vicinity of the closest stars and compressed into a short time-lapse movie, our solar system’s birth and evolution would present an eerie picture. From a large black cloud of molecular hydrogen, a star forms first, followed by whirling planets. Once settled in their orbits, the outer giant planets remain relatively inert, placid for billions of years beneath their whorls and bands of swirling gas. Even less happens on inmost Mercury after its magma oceans cool and crust over. The other three inner worlds are each a blue-green jewel of cloud, sea, and land, but in a flash Venus bakes beneath a pall of steam, and Mars withers and freezes. For most of the movie’s running time, Earth is the system’s most curiously variable world, a kaleidoscope of wandering continents, pulsing glaciers, erupting mountains, surging tides, and swarming greenery. In the last second before the time-lapse catches up to the present day, the Earth gains electric lattices of nocturnal lights and sparkling haloes of artificial satellites. The transformed planet ejects a handful of spore-like metallic flecks throughout the system. Five of them approach Jupiter and are flung off at solar-escape velocities, destined for parts unknown in the wider galaxy and cosmos. They are humanity’s fledgling interstellar probes, each launched by NASA: Pioneer 10 and 11, Voyager 1 and 2, and the Pluto-bound New Horizons.

  On February 14, 1990, the farthest and fastest of those probes, Voyager 1, turned its cameras back toward Earth for a final time from a distance of more than six billion kilometers, beyond the orbit of Pluto and high above the solar system’s ecliptic plane. At the insistence of Carl Sagan and other workers on the Voyager missions, the spacecraft sought to reproduce the iconic Apollo “Blue Marble” image, but from a distance one hundred thousand times greater. From so far away, the entire Earth was almost lost in the Sun’s diffractive radiance, but close inspection revealed our planet as a solitary azure point of light comprising less than a single pixel in Voyager 1’s transmitted image.

  Sagan called Earth’s image a “pale blue dot,” and went on to use the phrase as the title for one of his many bestselling books. In the decades since the Green Bank meeting, he had ascended to the pinnacle of practicing and popularizing space science, performing crucial work on planetary atmospheres and producing the wildly successful television miniseries Cosmos. With Frank Drake and other collaborators, Sagan had designed and curated a long-playing phonograph record to be sent to the stars with the Voyagers. Crafted from copper, aluminum, and gold, a copy of the record was bolted to the side of each spacecraft, ready for playback, complete with a magnetic cartridge, stylus, and pictogram instructions. In the emptiness of interstellar space each record should persist for untold eons, outlasting the Sun and the Earth alike. Any eventual encounter with another planetary system is improbable—if ever found at all, the records will most likely be recovered by some wildly advanced civilization traveling between the stars. Maybe even by our distant descendants, if we are so lucky. The Voyager records were vaingloriously utopian, and excluded references to such entropic human failings as crime, war, famine, disease, and death. Each contained recorded messages from President Jimmy Carter and United Nations diplomats, greetings in fifty-four languages, and 118 joyful photographs of life on Earth. Each would share the sounds of wind and rain, heartbeats and laughter, kisses and rocket launches, electroencephalograms and whale songs. Each would play the music of Bach and Beethoven, Mozart and Stravinsky, Peruvian panpipes, Javanese gamelans, and Chuck Berry performing “Johnny B. Goode” on his electric guitar. Each would be a murmur from the departed Earth, a golden memory of beings either sublimed into some unknowable future form or long fallen from their ancient flaws.

  To many humbled and earthbound souls living in a universe revealed year by year as increasingly aloof and uncaring, Voyager’s glimpse of far-off Earth and its messages to the stars became beacons of hope, perseverance, and wisdom, pure and noble expressions of the better angels of our nature. Meditating on the pale blue dot in an essay, Sagan poetically called it a “mote of dust suspended in a sunbeam.” It was “the aggregate of our joy and suffering” upon which “everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.” To Sagan, the image was a symbol of the cosmic folly of human divisions and geopolitical conflicts. “In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves,” he wrote. “The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. . . . [T]he Earth is where we make our stand.”

  Earlier in the same essay, Sagan touched on the difficulties of finding any plausible future planetary home for humanity. He thought that the pale blue dot approximated the view of Earth as seen from a starship arriving after a long interstellar voyage. He did not mention that it also replicated how our planet would appear through a first-generation TPF-style space telescope, though the thought perhaps crossed his mind. We would know from experience that our home planet’s pale blue came from its life-giving seas of water and clouds of water vapor, Sagan wrote, but he doubted whether an alien observer could surmise so much from Voyager’s single, spectrum-free image. More detailed inspection would be required.

  That inspection arrived ten months after Voyager 1’s historic image—on December 8, 1990, when Sagan masterminded a suite of Earth observations using the Galileo spacecraft, which was flying by our planet on a roundabout voyage to Jupiter. Examining the Earth as if it were a newly discovered alien world, Sagan and the Galileo team successfully confirmed Earth’s habitability, then detected its biosphere and technology, all from the depths of space and purely from first principles. They took the planet’s temperature in infrared light, and confirmed its polar caps, seas, and clouds were made of water. They found evidence of life in the oxygen-soaked, methane-tinged atmosphere, far out of thermodynamic equilibrium, as well as in the vegetation-filled continents, which reflected the spectral sign of light-absorbing chlorophyll, of photosynthesis, out into space. Powerful pulses of narrowband modulated radio waves from the planet’s surface hinted at technological civil
ization. The collective verdict was indisputable: much of the planet was literally covered with life, and something down there had been smart enough to build a global telecommunications network. Later, Sagan and his team turned Galileo’s instruments toward Earth’s Moon, finding to no surprise that, unlike our living planet, it was a desolate, dead rock. As pat and prosaic as Sagan’s Galileo observations may first appear, they constituted a potent control experiment, a standard of proof that could be applied to any planet, whether investigated via close-flying probe or by telescopes gathering light over interstellar distances.

  Examining the breadth of Sagan’s later work, it is hard to escape the conclusion that he was methodically preparing for any observational studies of potentially habitable exoplanets that might occur during his lifetime. We will never know for certain. His life was cut short in December 1996 at the age of sixty-two, after a two-year battle with bone marrow disease, only months after NASA’s administrator, Dan Goldin, had announced plans to build TPF. Even at the end, by all accounts Sagan was just as sharp and limber-minded as he had been in all the earlier decades of his scientific career. If Goldin’s initial projections for TPF’s launch in 2006 had held, Sagan would have been seventy-two when the telescope began uncovering any pale blue dots around nearby stars. Had he lived longer, he could have served as an authoritative elder statesman to guide and promote the next giant leap in humanity’s understanding of the universe. Instead, with Sagan’s passing and the eventual demotion of TPF to NASA’s technology-development dustbin, his Voyager and Galileo observations of Earth were quite possibly the closest astronomers would get to investigating a living, alien world for many generations to come.