Five Billion Years of Solitude (9 page)

From the audience, someone asked how many stars might lack planets entirely.

“It’s very hard to show that any star is devoid of planets,” Laughlin replied. “So it’s more useful to ask what percentage of stars have
planetary systems like ours. Data from RV surveys and from Kepler is now starting to show that stars with a Jupiter-mass planet in something like a ten-year orbit like our own system are fairly rare. This is something that I think at most only ten percent of surveyed stars can now support. At least as far as Jupiter is concerned, our solar system is somewhat unusual. Right now, the data are telling us that the archetypal planetary system is a Neptune-like planet in a warm, short-period orbit, but part of that is selection bias—those planets are easier to detect.”

He began to deliberately pace the floor, regaining the rhythm of his presentation by walking back and forth between the podium and a window. “We really don’t know much yet about the distribution of Earth-size planets in Earth-like orbits, but the expectation is that they will be abundant. Kepler’s going to tell us soon, I think—it’s easier to validate transits, even though they reveal small fractions of total populations. The small planets we’re detecting today create RV signals on their stars of the order of a meter per second. I’m walking a meter per second right now. Now, that’s an incredible accomplishment to detect such a small change in the motion of an entire star many light-years away, but it’s not quite enough: the Earth’s RV signal on the Sun is only about ten centimeters per second. Stars move more than that from interior pulsations and vibrations, and from material flowing around their surfaces—at any particular moment, a star is creating all that noise, introducing astrophysical jitter that contaminates the signal.”

There was an implicit warning within Laughlin’s carefully phrased remarks. The most tantalizing worlds—those that might resemble Earth and harbor life—were also some of the most difficult to find. A low-mass planet in a clement orbit about its star could often only be detected as a sliver of signal cresting above a sea of stellar noise. As the pressure mounted for RV surveys to turn up alien Earths orbiting nearby stars, it was also getting tougher to know what was actually real.

Faint RV planetary signals could be amplified, Laughlin told his audience, by lavishing a quiet star with attention, hammering away with hundreds or even many thousands of observations, all averaged over time
to beat down the star’s already low stellar noise. But the approach came with risks—a planet-hunting team fortunate enough to secure observing time on a world-class telescope and spectrometer might chase a star’s tantalizing signals for months or even years, only to ultimately discover that its potential planets were illusory. Careers and reputations would be forged or shattered on the barest probabilistic whiffs of planets emerging from a statistical haze. “[The] push toward lower-mass planets is part of an ‘arms race’ among the different competing groups,” Laughlin explained near his presentation’s conclusion. “You find planets, and then the time-allocation committees give you more time to find more planets. If at any point you don’t find planets, that’s it, you’re out of the game.”

•   •   •

F
or more than a decade after astronomers began regularly detecting exoplanets in the mid-1990s, the RV “game” had been limited to a contest between two great planet-hunting dynasties, one American, the other European. The first began in Pasadena, California, in 1983, while a struggling twenty-eight-year-old astronomy postdoc named Geoff Marcy was taking a long morning shower. Marcy’s research into stellar magnetic fields wasn’t panning out, and had been roundly criticized by a few senior astronomers. He felt incompetent, depressed, and burnt-out. As the water streamed over his downturned head, he realized that up until then his career had been mostly a failure, and that if nothing changed, it might end before it had even properly begun. He thought back to what had set him down his disastrous path of astronomy, when he had been a young boy wondering whether all the stars in the sky had planets. Where had his passion gone? Suddenly, an epiphany: if he was destined for failure, he should fail spectacularly, pursuing a topic he loved but few others took seriously. By the time he finished showering, he had decided to spend the rest of his perhaps-brief career searching for exoplanets.

Marcy was not as incompetent as he believed. His encyclopedic knowledge of astronomy, paired with a quick wit and the skills of a natural storyteller, made even the most abstruse astronomical topics comprehensible to laymen. He soon landed a junior faculty job at San Francisco State University, and in between teaching courses he pondered an RV planet survey, though his plans always seemed half-baked—the spectroscopic signals of planets would be impossible to discern without proper calibration. Things coalesced when he met Paul Butler, a younger student simultaneously pursuing a bachelor’s degree in chemistry and a master’s in astrophysics. Butler shared Marcy’s interest in exoplanets, and they became close friends. Together, they worked to find ideal calibration methods, until Butler came up with a solution: a glass vessel filled with iodine that could be attached to a spectrometer. Light shining through this “absorption cell” would project iodine absorption lines like hashmarks upon a star’s spectrum, allowing small spectral wobbles to be seen. Butler’s iodine cell would become the standard calibration technique for decades of RV planet searches.

In 1987, Marcy and Butler mated the iodine cell with the general-purpose “Hamilton” spectrometer built by Marcy’s former PhD advisor, the UC Santa Cruz astronomer Steve Vogt, and began their planet search. For years they used the spectrometer on various telescopes at Lick Observatory on Mount Hamilton, twenty-five miles east of San Jose, searching to no avail for extrasolar Jupiters around 120 nearby Sun-like stars. Butler left for a time to obtain his PhD at the University of Maryland, but continued to hone the duo’s data-analysis software, eventually sharpening the RV precision of their data from 15 to 5 meters per second. By the autumn of 1995 they were nearing the end of their patience when two University of Geneva astronomers, Michel Mayor and Didier Queloz, announced the discovery of 51 Pegasi b based on another RV survey conducted from the Haute-Provence Observatory in the south of France.

When they heard the news, Marcy and Butler rushed to observe 51 Pegasi for themselves, and within days saw the star’s telltale wobble
from its whirling hot Jupiter—a variety of planet they had not conceived of or looked for in all their previous years of searching. Revisiting their old data, they rapidly found two more giant planets around the stars 47 Ursae Majoris and 70 Virginis, retaking the lead in the burgeoning race of discovery and establishing a rivalry that would span decades.

In those early golden years, Marcy and Butler surged ahead in the race, propelled by nearly a decade of experience and their extensive back-catalog of data. By the turn of the millennium, they had discovered nearly forty close-orbiting gas giants. Each announcement was a news event—the discovery of exoplanets had yet to become truly routine. With their research featured on magazine covers and national newscasts, the duo abruptly found themselves in high academic demand, and soon secured more-prestigious positions. Marcy became a UC Berkeley professor, and Butler secured a job as a staff scientist at the Carnegie Institution for Science in Washington, DC. Though geographically separated, they continued their work together, ultimately utilizing their growing fame to expand their team to include Vogt as well as another brilliant planet hunter, the astronomer Debra Fischer. The group gained more funding and access to some of the best astronomy resources in the world, notably another Vogt-built spectrometer, HIRES, operating on the twin 10-meter telescopes of the W. M. Keck Observatory in Mauna Kea, Hawaii. HIRES could reach RV precisions of 3 meters per second, allowing it to discover smaller exoplanets in cooler orbits. But to reach potentially habitable worlds, even more precision would be required. Marcy began closing his intergroup e-mails with the exhortation “OMPSOD!”—One Meter Per Second, Or Death!

“The Swiss,” as Marcy’s and Butler’s Geneva-based competitors are invariably called despite having collaborators around the world, were not sitting idle while their American counterparts surged. They were expanding their team as well, and redoubling their efforts to find more planets. As both teams excelled, their competition became fierce. At a conference in June 1998, the American team announced their
discovery of Gliese 876b—the first planet found around a red dwarf star. The following day, the Swiss made an announcement of their own, saying they had detected the same planet days before the American announcement; they claimed to have confirmed their discovery some hours before the conference, but Marcy and Butler had beaten them to the podium. The American team would also beat them to peer-reviewed publication on the planet, and came away with credit for the discovery. In November of 1999, both teams nipped at each other’s heels to share the discovery of the first transiting planet, a hot Jupiter around the star HD 209458, after separately and nearly simultaneously observing the transiting world and submitting papers on the results. The rivalry deepened in 2002, when the Swiss released a paper claiming the detection of twin “hot Saturns” around the star HD 83443. Marcy, Butler, and Vogt also observed the star, but could find no evidence in their data to support both Swiss planets. Butler spearheaded the publication of a paper detailing the case against the Swiss claims, and months afterward the Swiss team retracted one of the planets, placing a dark blemish on their otherwise flawless record. In contrast, while working together the American team never retracted a single world from their tally. The Swiss never forgot about the time when Butler led the American charge against them. They would keep him far from their orbit ever after.

The Swiss, for their part, seized the lead in RV precision in 2004 with the debut of their HARPS spectrometer, developed in collaboration with the European Southern Observatory (ESO). Stabilized in a temperature-controlled vacuum chamber and mounted on a 3.6-meter ESO telescope in Cerro Paranal, Chile, HARPS proved capable of breathtaking RV precisions of slightly below 1 meter per second, giving the Swiss a decisive edge that they used to discover a multitude of smaller planets orbiting on the cusps of habitable zones. Some of the worlds were only a few times the mass of our own, and thus possibly rocky rather than smothered in heavy layers of gas. They were hopefully called “super-Earths.” Keck’s HIRES would receive upgraded
detectors that same year, boosting its precision closer to but not equaling that of HARPS. The Americans had more planets to their names, but they knew it was their competitors who were making faster progress toward detecting potentially habitable worlds. The Swiss had been the first to break the 1-meter-per-second barrier, and even with its upgrades HIRES was slightly below HARPS in performance. After their years of dominance, the Americans privately worried that their sudden disadvantages, albeit minor, could lead to the downfall of their team.

As the Swiss were developing HARPS in 2002 and 2003, Fischer, Vogt, Butler, and Marcy made grand plans of their own for what they hoped would be a superior piece of kit: the Automated Planet Finder, a 2.4-meter robotic telescope to be constructed at Lick Observatory and outfitted with a new spectrometer custom-built by Vogt to excel at precision RV measurements of a meter per second or less. Though it would be dwarfed by the light-gathering power of many larger ground-based telescopes, the APF’s advantage would be its singular focus. Almost all world-class telescopes were by necessity workhorses for the entire breadth of astronomy, with only a portion of their time devoted to planet hunting. The APF’s sole task, by contrast, would be to survey bright nearby stars, night after night, steadily accumulating RV signals for any accompanying small, rocky planets. The group selected Vogt to be the APF’s principal investigator. The project hit a snag, however, after the relationship between Marcy and Butler took a sudden turn for the worse.

Over time, the duo’s extreme success had pushed them apart and destabilized their friendship. They were no longer young—each man now sported dark circles beneath the eyes, a salt-and-pepper beard, and a head unburdened by more than a waning crescent of hair. After two decades of working together, much that had once seemed fresh and new now felt tiresome and constraining. Though he had initially been only a graduate student beneath Marcy, Butler’s development of the iodine cell and seminal contributions to RV data-analysis techniques had elevated him to equal stature with his longtime research partner. Yet
Marcy still acted as the group’s de facto leader and manager. Where Butler was taciturn and blunt, preferring the simplicity of actual planet hunting to the delicate nuance of press interviews and academic politicking, Marcy was loquacious, charismatic, and cunning, happy to speak at length in eminently quotable sentences about the team’s work and always careful to offer diplomatic praise for his competitors. With the Swiss, Marcy was cordial, even friendly, though they had for years collectively treated Butler as persona non grata. The almost universal propensity to overlook Butler in favor of Marcy had progressively led to a tangible divergence of the two men’s fortunes, as Marcy accrued the lucrative lion’s share of press mentions and professional awards.

Feeling underappreciated and eclipsed, Butler reached his limit in 2007 and abandoned Marcy to form a new planet-hunting team with Vogt, using instruments at Lick Observatory as well as facilities in Chile and Australia. Their dynasty was splitting into multiple shards. Fischer soon left the team, and her position as a professor at San Francisco State University, for a professorship at Yale, where she founded a planet-hunting group of her own and began building a new spectrometer, CHIRON, meant to rival and surpass HARPS. Marcy, by now a coinvestigator on NASA’s Kepler mission, remained at UC Berkeley and worked closely with a new protégé, the astronomer Andrew Howard, using Keck and HIRES to search for more planets and to study Kepler’s thousands of candidates. Where once there had been only two RV teams in serious contention for finding alien Earths, the disintegration of the powerful Marcy-Butler partnership had given birth to many, with still more upstart groups waiting in the wings to use a new generation of planet-hunting spectrometers being constructed and deployed at observatories across the globe. But along with the unified Swiss, the scattered, grizzled veterans of the crumbled American dynasty still had the best data, the best observatory access, and the best chance of finding rocky planets in stellar habitable zones. Marcy’s group, continuing its existing program while also first in line to drink from Kepler’s firehose, was the odds-on favorite to be first.