Five Billion Years of Solitude

by Lee Billings

  As it became clear that building both TPFs would easily be multibillion-dollar endeavors, outspoken support for the project in the wider U.S. astronomical community became ever more muted. The choice for NASA became an easy one as it struggled to balance the budgetary burden of its human spaceflight efforts against the discordant demands of astronomers and astrophysicists. In February 2006, it cannibalized some $3 billion from its science budget to support a handful of space shuttle flights and Bush’s Constellation program. The rapid push for life-finding space telescopes was effectively cancelled, officially demoted to become one of the agency’s numerous and indefinite technology development projects, a trickle-funded limbo where grand visions went to die. Without a major shift in policy and funding for NASA, the agency seemed set on a course to delay any planet-imaging telescope worthy of being called TPF until, at the earliest, the mid-2030s. In the meantime, the discoveries of more and more potentially Earth-like worlds would keep piling up. The transformative project Traub had uprooted his life for had, within less than a year of his arrival at JPL, crumbled to pieces. When I asked his opinion about TPF’s prospects in his lifetime, Traub told me with thinly veiled gloom that remaining optimistic had become part of his job description.

  “Professionally, I can’t get discouraged, because otherwise this would be a very, very depressing thing to do,” he said. “But when you start out to build a cathedral, it’s not a requirement that you build it before you die. They usually took a couple of hundred years. We aren’t building medieval cathedrals here, however. I think this is easier, and I do believe that if things had gone ahead as had been planned in that letter from 2004, if we had just been given the funds to go ahead, then we would be flying these telescopes more or less on the schedule that had been set. TPF-C would be nearing its launch, with TPF-I maybe at the end of the decade. There is nothing fundamentally new I have learned since 2004 to change that point of view. Now, technically speaking, none of this is easy. This is all hard compared to everything else I’ve ever done in my life, and everyone else working on this would tell you that, too. But right now, today, we do already have half a dozen ways to get the light of potentially habitable exoplanets. We’ve proved them in the lab. We need time to get the engineering correct, but not to invent new things. It’s really just a matter of building a big mirror with a little piece of glass in the focal plane, putting it in a big rocket, and putting some deformable mirrors in the back!”

  If it was so straightforward, I offered, maybe NASA wasn’t the only answer. Maybe the solution could come from private funding rather than government sponsorship.

  Traub shook his head. “There is nobody in the private sector with an incentive to spend money on something of this magnitude,” he said. “It’s almost impossible for people with money to spare to invest in a long-term project like this. That’s why the government does it. NASA didn’t decide to send men to the Moon; President Kennedy did. It’s the legislators and the administration that tell NASA what to do, so what it’s going to take is someone in Congress, someone in the presidency, feeling strongly about this and realizing that the first discovery of life beyond the solar system is an event that in all of history will only happen once. Do we want to be the ones who dropped the ball, who screwed up and didn’t move this forward? All we need is for our political leadership to decide this is something important for NASA and for our nation to do. I can guarantee we know exactly how to proceed if we are given the go-ahead. That’s my final thought on that.”

  • • •

  I had first met Traub the previous year, in late May of 2011, at a small conference held on the campus of the Massachusetts Institute of Technology in Cambridge, on the glass-sheathed top floor of its famed Media Lab. Entitled “The Next 40 Years of Exoplanets,” the conference had been conceived by the MIT astrophysicist and planetary scientist Sara Seager to mull over the field’s troubled recent past and its possible future redemptions, redemptions that could come via TPF or in some other unimagined form. Seager had invited Traub to discuss the Kepler results and to defend JPL’s role in TPF’s rise and fall. She had invited many other luminaries as well. Matt Mountain had come to make the case for a poor man’s TPF-O, explaining how a starshade could utilize less than a tenth of JWST’s observing time to deliver spectra of any small, rocky worlds around a handful of neighboring stars. A JWST starshade, he estimated, would cost about $700 million, though NASA would be loathe to spend a penny more than what was already being budgeted to get its flagging space-science flagship into orbit. John Grunsfeld was there, too, seemingly already preparing for his return to NASA, hinting that America’s astronauts were eager for challenging missions like assembling and servicing planet-finding telescopes in deep space far from Earth. His inner Tsiolkovsky emerged to declare that extinction awaited any single-planet species, and he optimistically predicted that solid proof of the first habitable exoplanet would come from a NASA space telescope on July 21, 2025—the fifty-sixth anniversary of humanity’s first footsteps upon the Moon.

  Seager was the conference’s ideal catalyst. She was still relatively young, on the eve of her fortieth birthday, possessing sufficient passion and longevity to keep her at the forefront of exoplanet research for the next forty years. Though young, she was already one of the most respected and accomplished workers in the field. She had embarked on a career in astrophysics hoping to delve into cosmology, to reveal the formative early life of the universe. When the exoplanet boom began, she rapidly changed course. Beginning in the mid-1990s, when she was only a graduate student working under the Harvard astronomer Dimitar Sasselov, Seager had performed the first detailed theoretical modeling of the structure and evolution of hot Jupiters’ atmospheres. At the time, many astronomers still thought hot Jupiters were illusory products of stellar variability and wishful thinking, and some viewed Seager and Sasselov’s work as foolishly risky. Yet by 1999, she had obtained her PhD from Harvard, and the wider astronomy community had sheepishly caught up with her: most everyone finally agreed hot Jupiters were real, and Seager’s models set gold standards for observational studies. In response, Seager surged ahead again, describing how a transiting hot Jupiter’s atmosphere could be investigated without having to first build something akin to a TPF. In Seager’s proposal, coauthored with Sasselov, she pointed out that starlight blasting through the planet’s upper atmosphere would beam spectroscopic information toward Earth that astronomers could then discern using existing ground- and space-based telescopes; she recommended looking in particular for signs of sodium, which she calculated should project a clear spectroscopic signature in optical wavelengths. At the time, no transiting planets had yet been found. A couple of years later, a team tried out Seager’s suggestion, using the Hubble Space Telescope to observe a newly discovered transiting hot Jupiter. As predicted, they found the spectral lines of sodium—the first detection of an exoplanet’s atmosphere. Through the years, Seager’s focus had increasingly shifted to the search for exoplanetary life, in which she performed groundbreaking work on how to characterize the environments of potentially habitable worlds. She made it no secret that she hoped to lead any eventual TPF mission that flew in her lifetime.

  Seager had organized the conference with an eye toward posterity, and had meticulously ensured that its proceedings were captured on video and archived online. She cut a slim, striking figure when she stood to deliver her opening remarks in front of the seated scientists, engineers, and journalists. She wore a funereal black A-line dress and blazer that matched her knee-high boots and the shoulder-length dark hair that framed her solemn face. A blood-red scarf encircled her neck. As always, she talked with a brisk, steely intensity that some of her colleagues found off-putting, though neither social disengagement nor a lack of compassion were its cause. Seager’s mind seemed to be permanently overclocked, processing information faster and more keenly than most of her fellow human beings could fathom; her algorithmic approach to interaction, her abruptly earnest pronouncements, her calc
ulated charm, all simply reflected that. She swept her eyes over the gathered crowd in the auditorium as she spoke, but often when offering her most fervent points, Seager paused to turn her piercing hazel gaze directly into the camera lenses, addressing an undefined audience of future generations.

  She had brought the conference together, she said, to plot how to continue the field’s wave of discovery in the face of the U.S. government’s budget crisis and the seemingly dwindling exoplanet boom. “What we think here, most of us who work on exoplanets, is that hundreds or thousands of years from now, when people look back at our generation, they will remember us for being the first people who found the Earth-like worlds, and I don’t mean Earth-size or Earth-mass. I mean Earth-like.” Nearing her fortieth birthday, halfway through life, she said she no longer believed those discoveries to be foregone conclusions. “So I convened all of you here, and that’s why we’re recording this, because we want to make an impact and we want to make that happen. We are on the verge of being those people, not individually but collectively, who will be remembered for starting the entire future of other Earth-like worlds. That’s why we’re here.”

  It soon became clear that even if everyone agreed the field’s sustainability depended upon searching for potentially habitable, potentially living planets around nearby stars, opinions strongly diverged about how such a search should take place. Charting a unified path through the coming years would be a struggle. David Charbonneau, a longtime friend of Seager’s who was now a planet-hunting Harvard professor, rose from the crowd to make a case against pursuing a mission like TPF. Charbonneau had led the team that detected the first exoplanet atmosphere using Seager’s technique. He wore a bright-yellow T-shirt emblazoned with the slogan “BIGGER THAN TrES-4,” a reference to a transiting planet he had helped discover in 2007 that was so light and puffy it could float on water like a piece of balsa wood.

  Oddball transiting worlds were one of Charbonneau’s specialties; he had risen to prominence in 2000 when he codiscovered the first one, a hot Jupiter orbiting the Sun-like star HD 209458. Since 2009, he had spent much of his time on the mEarth Project (pronounced “mirth”), a ground-based array of small 0.4-meter telescopes that sought transiting super-Earths around nearby red dwarf stars, also known as M-dwarfs. The relatively large size of super-Earths in comparison to our own planet, paired with the relatively small size of an M-dwarf compared to our Sun, collectively meant that in terms of contrast the super-Earth/M-dwarf pairing was the easiest of all potentially habitable planetary systems to see, and would probably prove to be the cheapest kind to characterize. Charbonneau said that those transiting would be particularly good targets for transmission spectroscopy, as first outlined by Seager and others, all without needing to build anything like a multibillion-dollar TPF.

  Such massive worlds would likely be quite alien, with unearthly thick atmospheres and squashed landscapes due to their stronger gravitational fields. Unchecked by actual data, debates raged over whether or not super-Earths could possess some form of climate-stabilizing plate tectonics like our own more diminutive planet. To harbor liquid water upon their surfaces, M-dwarf super-Earths would need to be perilously close to their small, dim stars, so close that tidal forces raised by the nearby star would sap energy from the planets’ rotations, causing many to lock one face toward their stars just as the Moon does to Earth. On such worlds, one light-bathed hemisphere would be eternally scorched by ionizing radiation from stellar flares, while the other would be veiled in endless night, with only a thin ribbon of constant middling twilight between the two. Depending on its composition, a tidally locked planet’s atmosphere could entirely freeze out onto the night side, or, if it persisted, drive steady gale-force winds between the disparate hot and cold hemispheres. If they were even habitable at all, no M-dwarf super-Earth seemed likely to ever top a list of Earth-like exoplanetary real estate.

  To Charbonneau, those environmental drawbacks and uncertainties were of little consequence, as was the fact that transit studies could only reveal a vanishing fraction of the nearby population of exoplanets. What was important was that transiting M-dwarf super-Earths could be found and studied relatively soon, at low cost, without the need to wait a generation or more. His argument was the distillation of a growing belief among some in the exoplanet community that directly imaging Earth-size planets in the habitable zones of Sun-like stars was a task so difficult it was effectively a nonstarter. In place of TPF, a host of smaller, less ambitious, less capable ground- and space-based mission proposals had emerged to sustain the astronomers during their travail in the budgetary wilderness. Like Charbonneau’s mEarth, most took their inspiration from the wildly successful Kepler mission, and revolved around searching for transits around nearby stars. Two years later, NASA would allot $200 million for the 2017 launch of one of those modest proposals, TESS, the Transiting Exoplanet Survey Satellite. TESS would be the successor to NASA’s Kepler mission, performing an all-sky search for transiting planets orbiting stars within a few hundred light-years of Earth.

  Sharpening his presentation, Charbonneau pointed out that while there were only 20 Sun-like stars within about 30 light-years of our solar system, there were nearly 250 M-dwarfs. Extrapolating from Kepler results, which suggested that smaller, cooler stars harbored large numbers of close-in low-mass planets, Charbonneau stated that within at most 20 light-years of the Sun, “we are guaranteed that there are [potentially habitable] bodies at the right place around those M stars” to transit as viewed from Earth. Pushing for TPF was a mistake, he opined, not only because there was insufficient funding, but also because “it’s foolish to devote twenty years of your life to something with too narrow a vision given the rate of discovery.” In Charbonneau’s view, younger astronomers would not and should not be willing to make such a lengthy investment in uncertain returns; missions like TPF and ATLAST would be doomed to wither and die on the vine for decades to come, and knowledge of any true Earth analogs would remain elusively out of reach. It couldn’t be helped.

  After a short break, Geoff Marcy, the doyen of American planet hunters, strode forward to tacitly critique Charbonneau’s dismissal of big, challenging space telescopes, which he implied was misguided and counterproductive. He began his remarks with his hands shoved deep in his pockets, uncharacteristically gazing down at the floor as he restlessly shifted his weight from foot to foot. He was ecstatic about Kepler’s results, he said, but angry about the last decade’s lack of progress and the diminished prospects for the next. Kepler’s results, he said, made the case for a TPF “extraordinarily compelling,” for it suggested the existence around nearby stars of a wealth of non-transiting potentially habitable worlds that would otherwise elude close investigation. TPF-I in particular, with its promise of high resolutions obtainable only through unfilled apertures, was “the only plausible future for astrophysics,” and yet “somehow NASA blinked.” He spread his ire around the room, blaming not only NASA but also the vassal-like space-science community for profound failures of leadership. In the picture he presented, it was as if the agency and JPL had acted as interferometers, splitting the exoplanet researchers into competing, clashing fronts that canceled each other out in nulling pulses of self-annihilative incoherence. As a result, the collective dream of a TPF had been relegated to the dark fringes of space astronomy, and a deep shadow had fallen across the field’s foreseeable future.

  “This is the history as I know it painfully well,” he recounted, recalling that he had served in 1999 on the inaugural TPF science definition team. “In 2000, NASA headquarters admonished us with a shaking finger from the administrator that we must build TPF-I, that we should all take classes, by the way, in astrobiology and molecular biology. . . . Then, around 2002, NASA said we should build a coronagraph, not an interferometer, and there’s not money for both, so it has to be the coronagraph! And then, remarkably, in 2004 NASA headquarters announced that we should build both! A coronagraph in the optical and an interferometer in the infra
red.” He shook his head, incensed. “I didn’t know how the money suddenly appeared to do both types of TPFs. We were being jerked around. For several years these two designs fought against each other, the coronagraph and the interferometer. . . . I think that was a pretty bad moment for a few years there. . . . And then of course the occulter came around, and the occulter cast a shadow, really, over the whole field!” The audience erupted in laughter, less from the simple joke and more to break the tension after the airing of so many uncomfortable truths.

  Winding down his presentation, Marcy made it plain his faith in NASA had been so shaken by the failure of TPF that he now wondered whether portions of the agency’s overlarge portfolio shouldn’t be entirely outsourced to the more agile private sector. Besides TPF, he did dream of one other great and worthy task for the agency in the next half century, one he articulated in a Tsiolkovskian appeal directly to President Obama. “Stand up and make the following announcement,” Marcy implored. “Say that before this century is out, we will launch a probe to Alpha Centauri, the triple star system, and return pictures of its planets, comets, and asteroids as soon as possible, even if it takes a few hundred years or a thousand years to get there. . . . It would be a great mission, to go to Alpha Centauri. It would engage the K-through-twelve children, it would engage every sector of our society, Congress, and so on. It would jolt NASA back to life, if we’re really lucky. . . . And of course any such mission should be an international one involving Japan, China, India, and Europe. . . . A mission to Alpha Centauri would bring the diplomatic coherence in the world that we need, as well as scientific progress.”