From one perspective, contemporary science can seem like an expensive inquiry into nature’s vast store of trivia. Few of us lie awake at night worrying about the mass of the Higgs boson, after all. String theory does not balance a chequebook, and loop quantum gravity will not drive your ten-year-old to soccer practice. It is easy to forget that the questions scientists are addressing are, at root, the oldest and simplest ones. How big is the universe we live in? What is it made of? What are we looking at when we look at the night sky?
University of Toronto professor Ray Jayawardhana’s Strange New Worlds: The Search for Alien Planets and Life Beyond Our Solar System surveys the modern answer to one of those simple, venerable questions: are there planets orbiting other stars and are any of them similar to Earth? And it does so in a lively, literate fashion.
The question is as old as recorded philosophy, and in the absence of hard answers it has often served as a blank cheque to the human imagination. Early in his book Jayawardhana cites an 1835 article in the New York Sun reporting the alleged discovery of blue unicorns and two-legged beavers on the surface of the moon—the article was a hoax, of course (although the publisher would allow only the “possibility” that it had been faked); but it drove the paper’s circulation to new heights, a genuine if slightly embarrassing testament to the public’s eager interest in the subject.
Such speculation has been a growth stock ever since, from the science fiction novels of H.G. Wells to the various incarnations of television’s Star Trek, the incantatory opening of which Jayawardhana references in his title. Often enough, however, science has played the role of Coleridge’s person from Porlock, puncturing gaudy dreams with drab fact. When the first detailed photographs of Mars were broadcast from the Mariner 4 spacecraft in 1965, the crystalline cities of Ray Bradbury’s The Martian Chronicles and the green-skinned warriors of Edgar Rice Burroughs’s A Princess of Mars promptly dissolved into the reality of a frigid, airless desert. (Since then Mars has begun to display an interesting personality of its own, including a primordial history of flowing water and the remote possibility of microbial life; but a hypothetical bacterium remains a sorry substitute for a Martian princess.)
Planets circling stars other than our own, however, seemed safely beyond the reach of tawdry reductionism (or respectable science, depending on how you look at it). In 1835—the same year the New York Sun conjured up its lunar unicorns and bipedal beavers—French philosopher Auguste Comte claimed that real knowledge of the stars was categorically impossible, “necessarily denied to us.” But as Jayawardhana writes, “Comte’s timing could not have been much worse. Unknown to him, several scientists across Europe were already making fundamental discoveries about the nature of light that would prove him wrong.”
That breakthrough was the science of spectroscopy, which identified consistent markers (Fraunhofer lines) for various elements in the spectrum of radiated light. Comte’s assertion that “we shall never be able by any means to study [the stars’] chemical composition” was instantly overthrown, as astronomers began to do exactly that. Doppler shifts in those same Fraunhofer lines made it possible to calculate the relative motion of the stars. The night sky had begun to yield up its secrets.
It remained an open question, however, whether any of those stars harboured planets, much less planets like Earth. One of the heresies for which Giordano Bruno was burned at the stake in 1600 was his assertion that the stars were suns like our own, with similar families of orbiting worlds. It was a reasonable idea even in Bruno’s day—scientifically, if not from the perspective of the Inquisition—but until recently there was no practical way to confirm it.
Strange New Worlds is the story of how the last three decades have transformed Bruno’s heretical surmise into established fact, and a survey of how tantalizingly close we are to even more intriguing discoveries. The key role is played once again by spectroscopy, augmented by generations of increasingly sophisticated technology: satellite observatories, radio telescopes, adaptive optics, high-speed computer analysis. The premise behind the research is relatively simple. Any star hosting a planet will wobble minutely under the gravitational tug of its companion. A small wobble implies a small planetary body; a larger wobble implies a bigger one. A wobble that repeats in a slow cycle implies a planet in a wide orbit around its star; a wobble with a fast cycle implies a closer one. The difficulty is that these signals are incredibly tiny and must be teased out of mountains of noisy data.
It sounds like a problem only a computer could love, but Jayawardhana consistently finds the human drama in it. The researchers he profiles tend to be soft-spoken visionaries, like astrophysicist Debra Fischer, for whom “observatories are monuments to humankind’s curiosity about the universe,” or the amateur New Zealand astronomer Jennie McCormick, whose backyard telescope contributed data that helped confirm the existence of a planet 15,000 light years from Earth. “It just shows that you can be a mother, you can work full-time, and you can still go out there and find planets,” McCormick says, a remark that surely would have confounded Giordano Bruno’s inquisitors.
Jayawardhana’s prose is not especially poetic, but nor, in this context, does it need to be. The poetry emerges from between the lines, in an implicit and widening revelation of our own very small place in a very large universe. The discoveries speak for themselves. By 2006, the number of known “exoplanets” had reached 200; by 2010, that number had doubled. Many of these worlds are so exotic that they almost defy description: “hot Jupiters” so close to their suns that their years are counted in hours and their surface temperatures would boil platinum, or frozen behemoths locked into looping orbits around red dwarf stars.
The smaller a planet is, the harder it is to detect, which means that a world resembling Earth—the grail of the planet-hunting business—remains beyond the limits of detection. But that is rapidly changing. NASA’s Kepler orbital observatory, launched in 2009, should be able to discern the presence of such planets, and according to recent reports its data are rich with promising results. Other and even more precise devices, including NASA’s Terrestrial Planet Finder and the European Space Agency’s Darwin observatory, are scheduled to launch within the next decade. Before long, as Strange New Worlds suggests, astronomers may announce the discovery of an Earth-sized planet circling a Sun-like star, located well within its so-called Goldilocks zone (not too hot, not too cold), with liquid water at its surface and an atmosphere rich in oxygen and methane, hinting at the presence of life.
The possibility that human beings could ever visit such a planet is extremely remote. Even with the best imaginable spacecraft, travel time to the stars would be measured in centuries if not millennia. Some things really are, as Comte said, necessarily denied to us.
But the knowledge that such worlds exist would transform the night sky from a glittering but empty desert into something deeper and warmer: an archipelago of distant islands, most hostile, some welcoming. And just as Apollo 10’s iconic photograph of the Earth as seen from the moon helped reconstruct our collective sense of ourselves and the fragility of our environment, the most profound and unpredictable effects of that knowledge will surely be on our own psyches. Looking out, we also look in.