Mirror Earth (9 page)

A century and a half later, William Herschel—the German musician who taught himself astronomy in middle age and went on to build the finest telescopes in existence, find the planet Uranus, discover infrared radiation, and much more—was a firm believer in extraterrestrials. The Moon was certainly populated, he was sure. In a letter to a friend in the Royal Society he wrote, “If you promise not to call me a Lunatic, I will … shew my real sentiments on the subject.” So was Mars, which he wrote, has an atmosphere, “so that its inhabitants enjoy a situation in many respects similar to ours.” So was the Sun. The people who live there don't burn up, he believed, because the fiery surface we see is actually the blazing top of a permanent cloud cover. The undersides of these burning clouds are cool, and the dark sunspots we see are breaks in the overcast, giving us a glimpse of the cool and comfortable surface that lies below.

While Herschel and many others populated just the solar system with their speculations, followers of the French philosopher
René Descartes, who did most of his work in the mid-1600s, theorized on a grander scale. Descartes rightly guessed that the stars were faraway suns in their own right. He stopped there, but one of his students, Bernard Le Bouvier de Fontenelle, took the next logical step. “Our Sun enlightens the Planets; why may not every fix'd Star have Planets to which they give light?” he asked the French in his 1686 book
Entretiens sur la pluralité des mondes
(Conversations on the plurality of worlds).

And so, from the early 1600s on, philosophers and scientists would debate the questions that would ultimately lead Frank Drake, the founder of SETI, to begin listening for alien signals in 1961 and would lead Geoff Marcy and Bill Borucki to begin searching for extrasolar planets in the mid-1980s. They couldn't test their theories, though. Despite the construction of more and more powerful telescopes through the late 1800s and early 1900s, there was no way to back up their ideas with observations. Planetary formation could, depending on whose theory you liked, be inevitable or improbable. Our solar system might be typical, or very rare.

With those same telescopes, however, astronomers kept finding new objects in the solar system—scores of asteroids starting in 1800; the planet Neptune in 1846; moons circling Uranus, Mars, Jupiter, Saturn, and Neptune throughout the 1800s; Pluto in 1930. Throughout most of that period, scientists became more and more convinced that at least some planets were populated—especially Mars and Venus—although Herschel's idea of creatures that walked the Sun never caught on.

By the late 1800s, almost all of that conviction was focused
on Mars. Venus was perpetually covered with a thick overcast that surrounded the entire planet. You could speculate about a dank, swampy surface, and many did, but speculation was the end of it. With Mars, by contrast, the surface was visible, in a blurry sort of way. Swimming in and out of view in that blur were two very notable features. First, while most of the surface was a reddish orange, the Martian poles were white, suggesting that Mars had icecaps, like those on Earth. The observers could even see the white spots wax and wane with the Martian seasons. That proved Mars had an atmosphere that could move melted, evaporated ice from one hemisphere to the other to fall as snow each winter.

But that was nothing compared with the evidence first reported by Italian astronomer Giovanni Schiaparelli in 1877. At the very edge of visibility, Schiaparelli said, he saw markings on the Martian surface. In an article published several years later, he wrote,

All the vast extent of the continents is furrowed upon every side by a network of numerous lines or fine stripes of a more or less pronounced dark color, whose aspect is very variable. These traverse the planet for long distances in regular lines, that do not at all resemble the winding courses of our streams.

Not only that: These
canali
, or channels, seemed to widen and narrow with the change of seasons, and some of them appeared to double into pairs of parallel channels. He continued,

Their singular aspect, and their being drawn with absolute geometrical precision, as if they were the work of rule or compass, has led some to see in them the work of intelligent beings, inhabitants of the planet. I am very careful not to combat this supposition, which includes nothing impossible.

In many of his scientific papers, Schiaparelli was careful to acknowledge that much of what he saw could also be completely natural, and that his eyes might even be playing tricks on him. Some of the other astronomers who also saw the
canali
were convinced that they were, in fact, optical illusions, but others were sure they were real. In other writings, Schiaparelli made it clear that he strongly favored the argument that many of the canals were engineered by Martians. The thickening, he believed, was a seasonal expansion of vegetation as the
canali
flushed with water and nourished crops on either side.

Schiaparelli was a model of caution and restraint, however, compared with Percival Lowell. Lowell, a rich Bostonian and the brother of future Harvard president A. Lawrence Lowell, became intrigued with Mars in the early 1890s. He built his own observatory under the clear skies of Flagstaff, Arizona, equipped it with a much more powerful telescope than Schiaparelli used, and began scanning Mars for evidence of the life he was already convinced was there. With that attitude, it's no surprise that he found it. “Mr. Lowell went direct from the lecture hall to his observatory in Arizona,” wrote astronomer W. W. Campbell disparagingly in a review of Lowell's popular
1895 bestseller
Mars
, “and how well his observations established his pre-observational views is told in this book.”

This end run around the scientific method didn't bother the press, however. MARS INHABITED, SAYS PROF. LOWELL, ran a headline in the
New York Times
on August 30, 1907. “Declares the Planet to Be the Abode of Intelligent, Constructive Life … Changes in Canals Confirm Former Theory—Splendid Photographs Were Obtained.” An editorial in the
Times
from around the same time says in part, “Harvard has ignored Prof. Lowell's discoveries of water vapor, vegetation, snow caps, and canals, always, more canals, on Mars. The people of this country support Prof. Lowell in his Martian campaign.”

Lowell died in 1916, still convinced he had discovered intelligent life on Mars. But within a few years after his death, the canals had vanished, as bigger and more powerful telescopes gave astronomers a sharper view of the planet. They were, as Schiaparelli had admitted might be the case (but Lowell hadn't), a trick of light, an optical illusion. For the general public, however, which had been reading about scientific claims of Martian life for decades, the idea of living Martians had become part of the popular culture.

It wasn't just public lectures and glowing newspaper stories. In 1898, H. G. Wells published the bestselling
War of the Worlds
. In 1912, Edgar Rice Burroughs, who a year earlier had been working as a wholesale distributor of pencil sharpeners, published
A Princess of Mars
, followed by nearly a dozen sequels. He went on to write a series about life on Venus as well, and one novel titled
Skeleton Men of Jupiter
. (Burroughs also
invented Tarzan of the Apes, by far his most famous character.) By the time Orson Welles turned
War of the Worlds
into a radio play in 1938, the idea of intelligent Martians was so plausible that some listeners thought an invasion was really going on—although the idea that hundreds of thousands of Americans fled their homes in panic is evidently an urban legend. Most of those who had listened to Welles's program the week before didn't panic, since he told them to stay tuned next time for the Martian invasion.

Even as aliens became a staple of B movies and TV shows such as
The Twilight Zone
and of breathless reports about UFOs in the 1950s—and maybe partly as a result—the topic moved out to the scientific fringe. The physicists Philip Morrison and Giuseppe Cocconi went out on a limb when they published a paper in 1959 titled “Searching for Interstellar Communications,” which suggested listening for alien radio signals. Morrison and Cocconi were no Percival Lowells; they didn't claim that extraterrestrials existed. “The probability of success is difficult to estimate,” they wrote at the conclusion of the paper. “But if we never search, the chance of success is zero.” Frank Drake independently began his search at the National Radio Astronomy Observatory in Green Bank, West Virginia—but he kept it a secret. The search for alien signals is still going on today, but without a lot of funding, and with the understanding that the search still has to overcome what astronomers call the “giggle factor.”

By the early 1960s, the Soviet Union had beaten America into space with the unmanned
Sputnik 1
satellite, and again with the first orbital flight by cosmonaut Yuri Gagarin. In a
Cold War panic, John F. Kennedy declared that America would demonstrate its superiority by beating the Soviets to the Moon. Money poured into the U.S. space program, which, despite waving flags and inspiring words about exploration and frontiers and understanding the universe, was mostly about showing the United States was better than the Communist enemy. Infused with money, a mandate to reclaim national pride, and a swelling staff of young scientists and engineers, NASA began shooting American astronauts into space and sending probes to the Moon, scouting for landing spots. The agency began sending robotic spacecraft out to explore the solar system as well—inward to Mars and Venus and out toward Jupiter and Saturn.

Whatever the original motivation, the
Mariners
and
Pioneers
and
Voyagers
brought back spectacular images and all sorts of data about the planets and their moons. The information, along with other observations, pretty much destroyed any remaining speculation about life on most of them. Venus turned out to be so hot that lead would melt on its surface. Mercury was covered with craters and relentlessly scorched by the nearby Sun. Jupiter, Saturn, Uranus, and Neptune were already known to have no surface at all until you got thousands of miles down into their gaseous atmospheres. Pluto, still a planet back then, was too frigid. But Mars proved to have ancient riverbeds; it clearly had no farmers or engineers, but it might once have had some primitive form of life, billions of years ago. The scientific search for life on other planets in our own solar system was revived, refocused on microbes rather than Martian princesses or skeleton men from Jupiter.

Thanks to more powerful telescopes than Galileo or Kepler or Herschel could have imagined, meanwhile, the active search for planets orbiting other stars, and not just theoretical speculations about them, was revived. NASA would try to play a major role here as well. But much of the agency's effort toward planet-searching would end up being wasted.

David Charbonneau arrived at Harvard in the fall of 1996, ready to literally take on the universe. He'd majored in physics as an undergraduate at the University of Toronto, concentrating on the physics of the cosmos just after the Big Bang. Thirty years earlier, a couple of radio astronomers at Bell Laboratories in New Jersey had stumbled on a mysterious whisper of static coming from all directions in the sky at once. The static turned out to be the feeble remains of an ancient flash of light from a time, more than thirteen billion years ago, when the universe emerged from a state of unimaginable density and heat and began to condense into the galaxies and stars we see today. The light was originally white-hot, but as the universe expanded, it cooled to red, and then moved out of the visible range entirely and into the microwave part of the electromagnetic spectrum, more of a faint glow by now than a flash.

Physicists realized that hidden within this cosmic glow—they named it the cosmic microwave background, or CMB—must be all sorts of information about the early universe. They
presumed, although they couldn't yet see them, that some spots should be a little warmer than average, representing spots of slightly higher than average density in the baby universe. These dense regions would have eventually formed into clusters of galaxies, presumably, while cool spots, with unusually low density, would have become the empty spaces in between. The warm and cool spots turned out to be so hard to detect that it took until 1992, and even then, the Cosmic Background Explorer (COBE) satellite that saw them could capture only the blurriest of images. If the spots hadn't shown up at all, it would have been a serious problem for the Big Bang theory. But while it confirmed the Big Bang, the data COBE sent back to Earth wasn't enough.

By the time Charbonneau was a senior at Toronto, physicists and astrophysicists had started to do follow-up studies from the ground to refine their understanding of the CMB, and they were starting to design new satellites that would improve on COBE. Toronto's Canadian Institute for Theoretical Astrophysics was in the thick of this, led by a prominent theorist named Dick Bond who was trying to figure out what the emerging patterns of hot and cold spots meant. “There were all of these wild data sets coming out of Antarctica,” Charbonneau told me one afternoon in 2010, “and from Saskatoon, in Saskatchewan. I was feeding off the excitement of the cosmologists.”

Charbonneau is now a full professor at Harvard, and our conversation took place as we walked from the Harvard Science Center, where he'd just finished teaching a class, up to the Center for Astrophysics a half mile or so away. It wasn't a leisurely walk. Charbonneau is extremely tall, so his stride covers a lot of ground. He's also extremely busy. He's got his own very time-consuming research project, he's a member of the Kepler science team, and he's also a very popular teacher. “Normally,” he told me, “I only teach one class, but this semester I've elected to teach three, because I really care about our undergraduate program.”