The Lonely Planet Hunters

• Five Billion Years of Solitude: The Search for Life Among the Stars
• Lee Billings
• Penguin Books (2013)

Any 20th-century kid hoping to be an astronaut could rattle off the names of the nine planets and go on to speculate about the possible existence of a tenth. But that was as far as it got. Trapped under our murky atmosphere, we couldn't even see those planets well; people were still claiming to see canals on Mars as late as the 1950s.

As for the rest of the universe, who knew? The kids' astronomy books I grew up with couldn't even explain our own solar system; one popular theory was that a passing star pulled material out of our sun that then condensed into the planets. Such close encounters would be very rare, so it was thought we might well be living on the only habitable world in the universe.

Live and learn. Pluto has since been demoted to the lowly rank of dwarf planet, while scientists have been finding "exoplanets" -- worlds orbiting other stars -- within a few dozen light-years of us. According to the Extrasolar Planets Encyclopedia, the current tally is 814 planetary systems including 1,077 planets and 179 confirmed multiple planet systems.

What's more, they are planets that were literally unthinkable a quarter-century ago: "hot Jupiters," for example, closer to their suns than Mercury is to ours. At least one system seems to have three planets in its "habitable zone," where water could be liquid (the planets themselves are far from habitable, however).

Science journalist Lee Billings tells the story of this revolution in astronomy in his new book, Five Billion Years of Solitude: The Search for Life Among the Stars. Like all revolutions, this one is rich in politics, deeply rooted in history and led by a few extraordinary people -- including Sara Seager, a Canadian-born astrophysicist at work on new ways to find more worlds.

The odds against finding alien civilizations

Billings begins his story with Project Ozma in 1960, when SETI (the search for extraterrestrial intelligence) began under the direction of Frank Drake. Using a big new radio telescope, Drake began periodically checking nearby planets to see if he could pick up radio signals. He couldn't; nor could generations of others.

Drake realized the odds: He didn't know which stars might have habitable planets, and if he did find a planet with life, it might not be transmitting. After all, we maintained radio silence for hundreds of thousands of years until Marconi. And we might not be transmitting for long: in the Cold War it seemed very likely that any advanced civilization might have a short life expectancy before it destroyed itself in nuclear wars.

In fact, one motive for Drake's search was to find out if other civilizations had discovered a way to avoid suicide. If they had, Drake reasoned, they might well last for hundreds of thousands or even millions of years.

Half a century later, we seem no closer to contact with alien civilizations, and SETI is running out of money. Yet since the mid-1990s, astronomers have been finding planet after planet.

They have several ways to do so. Radial-velocity spectroscopy measures the wobbles that planets cause as they move around their stars. The Kepler Space Telescope can actually follow the transit of a planet across the face of its star by measuring tiny variations in the star's light.

In hindsight, it's obvious that we would find the hot Jupiters first: enormous and very close to their stars, they exert the most obvious gravitational influence. But as techniques improved, we began to find gas-covered "mini-Neptunes" and rocky "super-Earths" in rapidly increasing numbers.

Interstellar gold rush

As Billings describes it, these techniques first emerged in the 1980s when a young astronomer named Geoffrey Marcy decided to search seriously for exoplanets. He teamed up with Paul Butler, who devised a way to calibrate spectroscopic signals. But not until 1995 did they succeed. Ironically, a Swiss team found the first hot Jupiter; Marcy and Butler, digging into their old data, found two more.

A kind of gold rush was on, with the Americans and Europeans in heavy competition. Funding and professorships followed, as well as scholarly battles over whether a given announced planet actually existed. But success had a price. Butler and Marcy eventually split up, each pursuing his own search with his own team.

These searches do not involve squinting through a super telescope and shouting "Eureka!" They involve feeding data into computer programs and seeing what comes out, and then refining the data some more. As in any other gold rush, conflicts arose over who owned the data and therefore the gold.

The key, then, was obtaining more and better data -- which meant more and better technology, all of it very expensive. Exoplanet discovery began in the prosperous years of the Clinton administration. But the U.S. space program was already in dire straits.

Houston, you have a problem

The space shuttle, designed as a cheap bus to get people and equipment into orbit, had turned into a black hole for taxpayers' dollars (and a death trap for some astronauts). Big rockets, capable of launching big telescopes, had been cancelled. If it couldn't fit in the bay of a shuttle, it wasn't going anywhere.

After 9-11, taxpayers' dollars were shipped to Baghdad to be pilfered by enterprising Americans and Iraqis with no interest in astronomy. President George W. Bush brought up the idea of a Constellation program to send men back to the moon as well as sending them to Mars. All that did was throw away still more dollars; President Obama killed Constellation in 2010.

With the public more interested in Star Wars and Star Trek than the real thing, paying for real space exploration has become a major problem; some researchers now look back on the 1990s as a golden age not to be repeated. The real protagonist of Billings' book emerges late in his story: Sara Seager, a Massachusetts Institute of Technology astrophysicist born and raised in Toronto.

Looking for life in unlikely places

As a Harvard Ph.D. student in the 1990s, Seager analyzed the atmospheres of hot Jupiters. During a stint at the Institute for Advanced Study in Princeton, she developed new ways to anticipate what exoplanet interiors and atmospheres might be like and how we might detect life on very unlikely worlds.

Moving on to MIT, she progressed rapidly while also supporting the development of a new class of telescopes -- Terrestrial Planet Finders, or TPFs -- even though 9-11, two wars, and the Great Recession made them increasingly unlikely. Other astronomers opposed the new telescopes as threats to the support of their own projects, Billings writes.

Seager's response has been to develop both new satellites and new sources of funding. Her Space Instrumentation group is building ExoplanetSat, a cheap "nanosatellite" about the size of a loaf of bread, that can piggyback on rocket launches and then study just one star for a couple of years.

Getting this and other TPFs into space could come from NASA or from the growing private-sector space industry. Seager is a co-founder of Nexterra Foundation, a nonprofit whose mission statement includes "undertaking an effort to locate, identify and create a map showing planets in the neighboring star systems."

And if that doesn't work out? "This sounds like a joke," she tells Billings, "but it's very serious: mining asteroids." She is scientific advisor to Planetary Resources, a company that plans to do just that. Its investors include Eric Schmidt and Larry Page of Google, and director James Cameron is another adviser. If the firm does indeed bring back vast quantities of platinum and other precious metals, Seager's share of the profits will pay for her own TPFs.

We are so accustomed to government funding for major space projects that private ventures sound crazy. But the Vikings and Basque fishers who first found Newfoundland were private venturers, and so were the companies that explored Canada for furs and Indonesia for spices.

As with computers, governments have covered the startup costs of space exploration. If they now lack the will to keep exploring, others will take up the task. On one of the pale blue dots they find, we may discover companions in this enormous universe, and an end to our five billion years of solitude.