Read Five Billion Years of Solitude Online
Authors: Lee Billings
By 2003, the Institute had secured $25 million in funding from Paul Allen, the billionaire cofounder of Microsoft, to build an innovative new instrument, the Allen Telescope Array (ATA), in a bowl-shaped desert valley some 185 miles north of San Francisco. Rather than construct a smaller number of gigantic (and gigantically expensive) dishes, the Institute would save money by building larger numbers of smaller dishes. Drake had spearheaded much of the ATA’s design. Three hundred fifty 6-meter dishes would act together as one extremely sensitive radio telescope, monitoring an area of sky nearly five times larger than the full Moon on a wide range of frequencies. Allen’s millions, along with $25 million more from other sources, were sufficient to build the ATA’s first forty-two dishes, which were completed in 2007. Significant funds to operate the fledgling ATA came from California state funding and federal research grants to the Radio Astronomy Laboratory at the University of California, Berkeley, which jointly ran the ATA with the Institute. Though only partially completed, the ATA still functioned well enough to support a SETI effort as well as a significant amount of unrelated radio astronomy research. It operated on an annual budget of approximately $2.5 million—at least until 2011, when funding shortfalls forced the entire facility into hibernation.
As I spoke with Drake in his home in June 2011, weeds were already growing up around the idle dishes at the shuttered ATA. Only a skeleton crew of four Institute employees remained attached to the facility, merely to ensure it wouldn’t fall into irreparable disarray. The ATA would not restart operations until December, buoyed by a brief flurry of small donations. The money raised was sufficient to fund only another few months of operations. The Institute was seeking a partnership with the U.S. Air Force, which later purchased time on the ATA to monitor “space junk”—cast-off rocket stages, metal bolts, and other debris that can strike and damage spacecraft. But that funding, too, proved only temporary, and time spent surveying space junk was time sucked away from the ATA’s SETI-centric goals. Unless more wealthy patrons swooped in with heavyweight donations, the ATA had very little hope of reaching its original target of 350 dishes—and during the long recession after the 2008 turmoil in the global financial system, potential donors were proving at least as elusive as any broadcasting aliens. Drake’s greatest dream seemed to be collapsing.
Aside from political and economic difficulties, there was another factor in SETI’s decline that was at once more scientific and particularly ironic: the rise of exoplanetology, a field devoted to the discovery and study of exoplanets, planets orbiting stars other than our Sun. Beginning in the early 1990s, as radio telescopes intermittently swept the skies for messages from extraterrestrials, a revolution occurred in astronomy. Observers using state-of-the-art equipment began finding exoplanets with clockwork regularity. The first worlds discovered were “hot Jupiters,” bloated and massive gas-giant worlds orbiting inhospitably close to their stars. But as planet-hunting techniques grew more sophisticated, the pace of discovery quickened, and ever-smaller, more life-friendly worlds began to turn up. Twelve exoplanets were discovered in 2001, all of which were hot Jupiters. Twenty-eight were found in 2004, including several as small as Neptune. The year 2010 saw the discovery of more than a hundred worlds, a handful of which were scarcely larger than Earth. By early 2013, a single NASA mission, the
Kepler Space Telescope, had discovered more than 2,700 likely exoplanets. A small fraction of Kepler’s finds were the same size as or smaller than Earth and orbited in regions around stars where life as we know it could conceivably exist. Emboldened, astronomers earnestly discussed building huge space telescopes to seek signs of life on any habitable worlds around nearby stars.
When the ATA briefly came back online in December of 2011, it began to survey those promising Kepler candidates for the radio chatter of any talkative aliens who might live there. No signals were detected before the ATA was sent back into hibernation, starved once again for money. SETI’s half century of null results could not be further from the ongoing exoplanet boom, where sensational discoveries could lead to media fame, academic stardom, and plentiful funding for researchers and institutions. For those interested in extraterrestrial life, exoplanetology, not SETI, was the place to be. As the search for Earth-like planets came to a boil, SETI was being frozen out of the scientific world.
When I asked Drake if we were witnessing the end of SETI, his blue eyes twinkled behind a knowing Cheshire Cat grin. “Oh no, not at all. This, I think, has been just the beginning. People presume we’ve been somehow monitoring the entire sky at all frequencies, all the time, but we haven’t yet been able to do any of those things. The fact is, all the SETI efforts to date have only closely examined a couple thousand nearby stars, and we’re only just now learning which of those might have promising planets. . . . Even if we have been pointed in the right direction and listening at the right frequency, the probability of a message being beamed at us while we’re looking is certainly not very large. We’ve been playing the lottery using only a few tickets.”
• • •
D
rake’s confidence that there are other life forms out there at all had its roots in a private meeting that took place shortly after Project Ozma.
In 1961, J. P. T. Pearman of the U.S. National Academy of Sciences approached Drake to help convene a small, informal SETI conference at NRAO’s Green Bank observatory. The core purpose of the meeting, Pearman explained, was to quantify whether SETI had any reasonable chance of successfully detecting civilizations around other stars. The “Green Bank conference” was held November 1–3, 1961.
The invite list was star-studded and short. Besides Drake and Pearman, three Nobel laureates attended. The chemist Harold Urey and the biologist Joshua Lederberg had both won Nobel Prizes in their fields, Urey for his discovery of deuterium, a heavier isotope of hydrogen, and Lederberg for his discovery that bacteria could mate and swap genetic material. Both were early practitioners in the still-nascent field of astrobiology, the study of life’s origins and manifestations in space. Urey was particularly interested in the prebiotic chemistry of the ancient Earth, and Lederberg worked to define how alien life on a distant planet might be remotely detected. As the conference was underway, one of the guests, the chemist Melvin Calvin, was awarded a Nobel for his elucidation of the chemical pathways underlying photosynthesis.
The other attendees were only slightly less celebrated. The physicist Philip Morrison had coauthored a 1959 paper advocating a SETI program just like the one Drake undertook in 1960. Dana Atchley was an expert in radio communications systems and president of Microwave Associates, Inc., a company that had donated equipment for Drake’s search. Bernard Oliver was vice president of research at Hewlett-Packard, and already an avid SETI supporter, having earlier traveled to Green Bank to witness Drake’s first search. The Russian-born American astronomer Otto Struve, the director of Green Bank observatory, invited one of his star pupils, a soft-spoken NASA researcher named Su-Shu Huang. Struve was a legendary optical astronomer, and one of the first who seriously considered how to find planets orbiting other stars. He and Huang had worked together studying how a star’s mass and luminosity could affect the habitability of any orbiting planets. The neuroscientist John Lilly came to Green Bank to present his ideas on interspecies communication,
based on his controversial experiments with captive bottlenose dolphins. A dark-haired and brilliant twenty-seven-year-old astronomy postdoc named Carl Sagan was, at the time, the youngest and arguably least distinguished name on the guest list. Lederberg, one of Sagan’s mentors, had invited him.
It fell to Drake to arrange the agenda. A few days before the conference began, he sat down at his desk with pencil and paper and tried to categorize all the key pieces of information needed to estimate the number,
N
, of detectable advanced civilizations that might currently exist in our galaxy. He began with the fundamentals: surely a civilization could only emerge on a habitable planet orbiting a stable, long-lived star. Drake reasoned that the average rate of star formation in the Milky Way,
R
, thus placed a rough upper limit on the creation of new cradles for cosmic civilizations. Some fraction of those stars,
f
p
, would actually form planets, and some number of those planets,
n
e
, would be suitable for life. From astrophysics and planetary science, Drake’s musing entered into the field of evolutionary biology: some fraction of those habitable planets,
f
l
, would actually blossom into living worlds, and some fraction of those living worlds,
f
i
, would give birth to intelligent, conscious beings. As his considerations shifted to the rarefied realms of social science, Drake became restless. He sensed he was nearing the end of his categories and the outer limits of reasonable speculation. He doggedly forged ahead. The fraction of intelligent extraterrestrials who developed technologies that could communicate their existence across interstellar distances was
f
c
, and the average longevity of a technological society was
L
.
Longevity was important, Drake believed, because of the Milky Way’s sheer size and immense age, and the inconvenient fact that nothing seemed able to travel through space faster than the speed of light. Approximately 100,000 light-years wide, and thought to be almost as old as the universe itself, our galaxy presented a huge volume of space and time in which other cosmic civilizations could pop up. If, for example, the average lifetime of an advanced technological society was a few
hundred years, and two such societies emerged simultaneously around stars a thousand light-years apart, they would have essentially no chance of making contact before various forces brought the communicative phases of their empires to an end. Even if one somehow discovered the other, and beamed a message toward that distant star, by the time the message arrived a millennium later, the society that sent the message would no longer exist.
If one were to multiply all of Drake’s factors together using plausible figures, conceivably a ballpark estimate of
N
would emerge. The terms were interdependent; if any one of them had a vanishingly low value, the resulting
N
, the estimated number of detectable technological civilizations at large in the Milky Way, would drop precipitously. Strung together, they formed an equation of sorts that, if it did not yield an accurate estimate of contemporaneous cosmic civilizations, at least helped quantify humanity’s cosmic ignorance.
• • •
O
n the morning of November 1, after the guests were seated and sipping coffee in a small lounge in the NRAO residence hall, Drake rose and strode forward to present what he’d come up with. But rather than address the room from the central lectern, he kept his back turned and scratched out his lengthy figure on a nearby blackboard. When he put down the chalk and stepped aside, the board read:
N = R f
p
n
e
f
l
f
i
f
c
L
That string of letters has come to be known as the “Drake equation.” Though Drake had intended it only to guide the next three days of the Green Bank meeting, the equation and its plausible values would come to dominate all subsequent SETI discussions and searches.
At the time, only one term,
R
, the rate of star formation, was reasonably constrained. Astronomers had already closely studied several
star-forming regions in the Milky Way. Based on that data, the astronomers in the group quickly pegged
R
at a conservative value of at least one per year within our galaxy. They also chose to focus on Sun-like stars. Stars much larger than our own were also far more luminous, and burned out in only tens or hundreds of millions of years, leaving little time for complex life to arise on any orbiting planets. Stars much smaller than the Sun were far more parsimonious with their nuclear fuel, and could weakly shine for hundreds of billions of years. But to be sufficiently warmed by that dim light a planet would need to be perilously close to the star, where stellar flares and gravitational tides could wreak havoc on a biosphere. Sun-like stars struck a balance between the two extremes, steadily shining for several billions of years with sufficient luminosity for habitable planets to exist far removed from stellar fireworks.
In 1961, no planets beyond our solar system were yet known, so the estimate of
f
p
relied only on indirect evidence. It emerged from a discussion between Struve and Morrison. Struve had performed pioneering work decades earlier, measuring the rotation rates of different types of stars. He found that the very hot, very massive stars larger than our Sun spun very fast, while stars like our own, as well as those that were smaller and cooler, spun more slowly. The difference, Struve thought, was that spinning planets accompanied the stars more like our Sun, sapping the stars’ angular momentum and reducing their spin rates. However, roughly half of the known Sun-like stars were in binary systems, co-orbiting with a companion star that could also affect their spin. In such a system the pull of each star upon the other, it was thought, might disrupt the process of planet formation. Struve speculated that only the other half, the singleton suns, would be likely to form planets. He was so convinced that planets were common around Sun-like stars that almost a decade earlier, in 1952, he had published a paper laying out two observational strategies to find them, presaging the exoplanet boom by a half century. Struve’s estimate that half of all Sun-like stars had planets was too high for Morrison, who guessed that even around many
solitary stars only scattered asteroids and comets would form. He thought
f
p
might be as low as one-fifth.