by Sara Seager
Pioneers can be ruthless. I wrote Dave: You are a fantastic scientist and time will show that. Then I told him what he already knew. He should still publish his findings, regardless of what his competitors did. That paper would matter more in the end than a press release. Time will tell the truth, I wrote.
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The more immediate truth was that one race was over, and a new one had begun. That walk across campus with my dog was the last break I would have for weeks. I had been turning over an idea—a genuinely original one—and the successful use of the Transit Technique gave it a greater urgency. I was practically swollen with it. A lot of science, especially pioneering science, relies on intuition. You’d be surprised to learn how many of our most significant discoveries began as a hunch, as a feeling. I didn’t have any evidence that my idea would work. But I was doubtless.
I had realized that the Transit Technique might help reveal something more than the black silhouette of a planet. Immediately around that tiny, partial eclipse, the same starlight that was being blocked by an exoplanet would pass through its atmosphere. The starlight would reach us, but not the way regular starlight reaches us. It would be filtered, like water running through a screen, or a flashlight’s beam struggling through a fog.
If you look at a rainbow from a distance, its many colors form a perfect union. But if you look at a rainbow more closely, using an instrument called a spectrograph, you can see gaps in the light, minuscule breaks in each wavelength like missing teeth. Gases in the solar atmosphere and Earth’s own thin envelope interrupt the transmission of sunlight, the way power lines cause static in a radio signal. Certain gases interfere in telltale ways. One gas might take a bite out of indigo, while another gas might have an appetite for yellow or blue.
Why couldn’t we use a spectrograph to look at the starlight passing through a transiting exoplanet’s atmosphere? That way we could determine what sorts of gases surround that exoplanet. We already knew that large amounts of certain gases are likely to exist only in the presence of life. We call them biosignature gases. Oxygen is one; methane is another. Maybe the way to find Bigfoot really was by seeing his breath. We could start with Hot Jupiters, the planets we already knew, and their more easily detectable atmospheres. Like a skunk’s spray, their traces of sodium and potassium would stand out amid the company of less potent atoms.
I kept my idea to myself, because I knew it was great—I was the first to see the potential of the Transit Technique for studying atmospheres—and now I knew, too, that great ideas get stolen. Dimitar Sasselov, my former PhD supervisor, was the only person I told about my theory, and he offered to help me bring it closer to practice. When we had worked out the details, I published a paper extolling what Dimitar and I called “transit transmission spectra.” Reading the gaps in rainbows.
My paper received considerable attention. NASA was accepting proposals to use the Hubble Space Telescope; within a few months of publication, one team cited my work and won the rights to study the light that passed through the atmosphere of a transiting Hot Jupiter. I was furious not to be included on that team, which chose an older male scientist over me.
Within two years, their work revealed the first exoplanet atmosphere. It didn’t surround another Earth, but my premise had worked. We had seen our first alien sky. I had profoundly mixed emotions on the day of the announcement. My theoretical efforts had triumphed, but I still felt as though I hadn’t been invited to the party I had helped to throw.
News of the discovery was embargoed from the public until one o’clock on a Tuesday afternoon. I told John Bahcall that I’d be ready to talk about it at 1:01 P.M. Every Tuesday there was a formal lunch called (imaginatively enough) Tuesday Lunch, at which John took his seat at the head of a horseshoe-shaped table filled with some of Princeton’s finest minds. I was proud to join them. John had a habit of cutting off boring speeches by clanking his glass, terrifying some of my colleagues, but I wasn’t scared. He was won over by careful, quantitative work, and I had done the work. I stood up and explained what others had done with what I had done, the chain of succession of my idea, from my lamp-lit desk to deepest space. The thought made me breathless. We had traveled light-years. It hadn’t taken any time at all.
John smiled with pride, and I warmed in his admiration. But he was far from satisfied. “What’s next?” he said.
I was coming to understand that I would ask myself that question every day for the rest of my life.
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Life doesn’t just need certain gases to survive. It also needs certain solids. It needs a rock to stand on. Perhaps, I thought, transiting exoplanets could prove valuable in yet another way. Radial velocity gave us the mass of an exoplanet. By watching that same exoplanet in transit, and measuring how much of its star it eclipsed, astronomers could now determine its size. High school physics teaches us that mass divided by volume yields density, and given an exoplanet’s density, we would have a pretty good idea of its construction materials: Dense would probably mean rock. We were still far away from seeing small, rocky planets, but here was a way we might home in on them sooner than we might with something like the Terrestrial Planet Finder. If astronomers could find a planet made of rock that also betrayed atmospheric evidence of biosignature gases, we could be looking at another us.
I turned my full attention to the avenues of discovery opened by the Transit Technique. I didn’t have much interest in confirming the existence of exoplanets that we had already discovered. I wanted to do better. I wanted to find new worlds passing in front of new suns.
Like every investigation into space, the Transit Technique had its complications. Bodies don’t often align. We would need to see the smallest passages, a tiny speck on an endless horizon, and we would have to see those passages repeat, as regularly as an orbit. That would require our looking at the same star for long periods. If aliens were using the same technique to find us, they would have to wait at least a year to confirm that Earth is a planet. (Closer to two years if they had just missed us the first time around.) The bigger problem, as far as my hopes were concerned: Even if we could somehow train a camera on an exoplanet during its transit in front of its star, what would we see? We’d see what we see of the moon during an eclipse. We’d see its silhouette, but nothing of its surface. We’d see black. I wanted a familiar blue dot in the sky. I wanted alien oceans, evaporating into alien clouds.
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Happily, walking in the footsteps of Einstein at the Institute made me feel capable of miracles. Not coincidentally, I was also in a place where I could finally make a friend. I still had a hard time navigating social situations; once, dressed nicely for a work event, I said to Mike, a little excitedly, “I can pass for normal!” He smiled. “Yeah, until you start talking.” Despite my being among so many like-minded colleagues, I sometimes saw things too starkly. I might change my mind about something, but if I did, I would swing from one extreme to the other. I rarely saw gray.
Gabriela was far from gray. A blond, blue-eyed Mexican astronomer, she was working on her postdoctoral fellowship, shuttling between Princeton and astronomy institutes in Chile. Gabriela and I soon saw each other as allies. We were both young, both ambitious. We both wanted to join the ranks of discoverers. Gabriela could also apply to use Chile’s enviable ground-based telescopes, which, for me, was like finding out your crush happens to come from money. At the time, the Institute’s offices were under renovation, and Gabriela and I huddled in a cloud-white trailer in a corner of the grounds. Spending time with her was a little like spending time with Mike: We were two of a distant pair.
Gabriela was incredible at math. It flowed through her more innately than music; it was something like spiritual. She had a preternatural ability to design simple yet expansive algorithms, and her access to telescopes meant that she could collect new data to feed them. I was good
at interpreting those numbers with my efficient computer code. Gabriela was the library; I was the reader.
We set ourselves the immodest goal of finding the first previously undiscovered exoplanet using the Transit Technique. Together we shared that tingle of anticipation known only to explorers, flush with the almost childlike joy that fuels every adventure. Like other astronomers trying to stake the same claim, we thought it best to use a telescope with a wide-field camera, capable of monitoring tens of thousands of stars at a time. We wanted to buy multiple tickets for the same lottery. Gabriela and I also knew that we wouldn’t be able to find an Earth-size planet just yet. A new Hot Jupiter, massive with a short orbit, would still be a titanic discovery in every sense.
Gabriela and I began hanging out beyond work, too. Mike liked her, and the three of us had frequent dinners together. She even looked after our menagerie of pets when we went on another long Arctic canoe trip. Gabriela and I became a team and, with time, a successful one. She flew to the telescope in Chile and diligently couriered tapes filled with astronomical data to me. I ran the data through my new lines of code, based on her stunning algorithms. We felt on the verge of greatness.
There was one moment when Gabriela and I thought we’d found a planet. We were strung through with adrenaline. Astronomers all over the world were trying to beat us, and we were trying to beat them, but making a claim that proved untrue would destroy our careers. We looked at the data and had to admit that something wasn’t quite right. At the end of our three weeks of allotted observing time, Gabriela flew home from Chile. We sat down in her office at the Institute to solve our dilemma. It was long past dark. Harsh fluorescent light reflected off our cherry tabletop as we scribbled away, pounding through algebra. Papers covered with equations piled up around us. Some fell to the floor. In that chaos we confirmed that we were seeing bodies in transit, absolutely. But the shape wasn’t right; the numbers didn’t add up. We looked at each other and didn’t know whether to laugh or cry.
We came to the realization at the same time: We hadn’t found a planet. We’d found a strange tangle of stars—what astronomers today call a “blend.” One star had passed in front of another, but a third, nearby star was contributing just enough light to the equation to lessen the starkness of the eclipse. It made a star look the size of a planet. Our only victory was that we had kept our confusion private.
Gabriela and I never did succeed. During our shared quest, she answered frequent questions from an older, famous astronomer. She thought he was just curious, interested in our progress and perhaps impressed with our strategy. Later that summer we found out he was competing with us. He didn’t steal our secrets; Gabriela gave them away. I was frustrated with her and with the situation—the other professor would have probably succeeded even without his duplicity. Time will tell the truth. Gabriela was devastated. I thought she would pull out of her dive and we would redouble our efforts in the ways that only she and I could. But she never recovered her enthusiasm for our project, and it felt as though she was also losing her interest in me. I felt let down. Abandoned.
In the fall of 2002, the older professor’s team put out a list of transiting planet candidates, including a previously unknown planet, OGLE-TR-56 b, in the constellation Sagittarius. Another team used radial velocity to confirm the finding, winning the accolades that come with being first. I spent two days crying. My father was visiting and took me to New York City for an afternoon. I told him of my disappointment while we walked the crowded streets; he bought me some camera equipment, as if to tell me that there were millions more things still to see.
Then I had a conference in Seattle to attend, and Mike and I took the chance to go on a long hike on Vancouver Island. He didn’t understand why being first in such an esoteric way mattered. His inability to understand my sadness was maddening, but he also helped give me a sense of perspective. My work would have its highs and lows, but Mike would always be there. Nothing had changed in the real world. I watched a bald eagle fly through a river canyon in front of me and thought: Everything is going to be okay.
In the middle of that race to find the first transiting exoplanet, my near-disaster with Gabriela led to a different kind of achievement. The equations that describe the dimming of starlight held another secret: They could be used to calculate the density of a planet-hosting star, which would help us eliminate false positives, such as the effects of our mischievous trio. We stayed up late one night and figured it all out—how our wrong could help others make sure they were right. It was hard for me to sit with Gabriela to write up our work for publication, staring into the heart of our dissolving partnership, but we could still salvage something of our time together. We published the lessons of our near miss, and that paper became one of my mostly widely cited. It was the consolation prize I received in exchange for the end of our friendship.
CHAPTER 5
Arrivals and Departures
I wanted to have children. I was in my early thirties, and I had always imagined that I’d have children one day. It would be almost hypocritical to dedicate myself to finding other life on another Earth and not bring new life to this one. But now it became more than a desire or an exercise in completeness; it was a need. I could feel my body demanding to carry a baby.
Mike did not share the feeling. Pets were one thing, he said. Children were something else. (I congratulated him on his observational skills.) I didn’t see a lot of room for compromise. We had talked about children before we were married, and he had agreed to the idea in principle. Practice, as always, was a different matter. It was time for him to make another decision about what he really wanted in life.
Late in 2002, after three years with John in Princeton, I was offered a position at the Carnegie Institution in Washington, D.C., as a senior researcher. The Institution was founded in 1902 by Andrew Carnegie, a safe haven where scientists are afforded the resources to follow their ambitions to their limits. A celebrated astronomer named Vera Rubin had retired, opening a place. I asked John whether I should fill it. His job was to find his postdocs permanent positions elsewhere. We were all meant to be just passing through Princeton. He knew that, the way parents know that their children will one day leave them. That doesn’t make their leaving any easier. I don’t think John wanted to lose me. He didn’t want to tell me not to go, either.
“Well, Vera did all right,” he said.
That was his way of giving me one last blessing. I was on my way.
Before I could start my job, I had to get a green card. I couldn’t leave the United States while I was waiting for it, so that summer Mike and I couldn’t take our usual canoe trip north. We went to paddle the Grand Canyon instead. It was some of the biggest water I’d seen. My canoe went into a trough and I couldn’t see beyond the crests of the churn around me; I was overwhelmed by the pure power of the river and retreated to the relative safety of our group’s raft. Lava Falls challenged even our guide, who flipped his kayak. Mike, however, took it on in an open boat. He looked so skilled, he paddled so flawlessly, that strangers shouted their admiration to him from the shore.
Soon after Mike and I moved to Washington, I was pregnant. I was elated. I began having recurring dreams of a daughter with red hair and blue eyes, Mike in miniature. I didn’t have any conscious preference for a son or a daughter, but those dreams were as vivid as my dream of our survival during that long-ago night on the esker: I was sure that we were going to have a girl. Mike began subscribing to my certainty. He wanted to name her Kira. He must have really liked that book. Since we couldn’t have a dog and a child with the same name, we renamed our loyal, brindled canoe companion “Tuktu,” the Inuit word for caribou. Then we waited for the new, hopefully less fearsome-looking Kira to join our growing family.
Out popped Max.
I was drained after thirty hours of labor, but I can remember so clearly when Mike first held him. Max was perfect, 10-out-of-10 on his Apgar scor
e. His thick, dark blond hair looked as though it had been trimmed and combed by a barber. He had sky-blue eyes like Mike—my dreams had been accurate there—and they regarded each other with identical stares. They looked so alike in that moment. Their faces shared an expression that wasn’t joy or sorrow or fear; it didn’t even look much like love. They were both totally surprised to see each other. They shared the sheerest awe.
Two years after Max came Alex. (His middle name is Orion, the constellation that dominated the western sky on the night of his birth.) I had to concede that both of my children were indisputably boys. I wanted to have more kids, maybe a red-haired girl named Kira next time, but Mike felt that he had met his end of our non-compromise. Two children were more than enough for us to handle. Rationally, I could see his point—there is something scary about being outnumbered by your offspring, and there aren’t many canoes built for more than four—but I had been so happy when I was pregnant. I glow thinking about it even now: all of that hope, all of that possibility, coming to life inside me. I tried not to feel wounded when Mike wanted to race off for the fastest post-baby vasectomy in reproductive history. I was upset, but his surgery put an end to our debates.
NASA was more open to further additions. In 2003, the agency launched another space telescope, Spitzer. It was a minor miracle of engineering. Unlike most telescopes, including Hubble, Spitzer didn’t capture visible light; it detected infrared. That was important, because stars and exoplanets both emit infrared light in the form of thermal radiation. (A little more than half of our sun’s light is infrared. You can’t see it, but you can feel it. Infrared is why places get warmer in the sun than in the shade.) We still had no way to perceive exoplanets in wavelengths our eyes can see, since their stars remained too bright. But exoplanets, especially the biggest and hottest of them, compete a little better in the infrared. The best of their light comes in the form of heat.
