Earth to Universe: Do You Read?

Geoff Marcy has to work nights, and his graveyard shifts last three or four days at a time. He arrives at work 2200 miles from home with heavy eyes and jet lag from crossing two time zones. But what choice does he have? You can't study the stars with the sun in the way. And the mammoth telescopes used by astronomers such as Marcy are built far from the air- and light-pollution that muck up the crystalline purity of the night sky.

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Marcy had it tougher a few years ago. Then he wasn't only exhausted, he was also an unknown. Today he is the king of planet hunters, answering questions asked for thousands of years by sky watchers who imagined distant worlds. If gray, saucer-eyed extraterrestrials are hovering overhead, they haven't provided enough evidence to satisfy the hundreds of scientists who spend their careers looking for less-fanciful signs that we are not alone. These researchers probe meteorites from Mars for evidence of ancient bacteria, listen for radio messages from deep space and search the stars for worlds that might support microbes or mammals or (continued on page 235) Earth to Universe(continued from page 196) intelligent beings. Marcy can't yet say if any have life, but he's finding planets all over the place.

Marcy and his colleague Paul Butler discover planets not by peering through a telescope--no working astronomer does it that way anymore. Instead, they use computerized telescopes with 33-foot mirrors to capture light from objects so far away we can't fathom the distance. Marcy's favorite is the Keck, which sits atop the 14,000-foot peak of the dormant volcano Mauna Kea in a Hawaii most visitors wouldn't recognize. Gentle tropical breezes do not blow here. Palm trees do not sway. The only difference between December and July is that July has blizzards, and the thin air is only technically breathable. Even standing still, you'll develop a terrific headache and nausea.

Mauna Kea is paradise to Marcy, because the Keck lets him see as close as he can to forever. Prior to 1995, only four people had found planets invisible to the naked eye: William Herschel discovered Uranus in 1781, John Couch Adams and J.G. Galle found Neptune in 1846 and Clyde Tombaugh located Pluto in 1930. Searching among 700 of the stars nearest the Earth, Marcy and Butler have found 12 planets, each orbiting its own sun. Other astronomers have discovered three more, for a total of 15, and the number won't stop there. Evidence of new planets, Marcy says, "is coming down the conveyor belt."

Scientists have reason to believe that at least one future astral discovery will be teeming with life. First, if life exists elsewhere in the universe, it almost certainly does so on a planet, or on a moon that orbits a planet. Photographs taken by the Galileo explorer have revealed a half-mile-thick layer of ice covering Europa, one of Jupiter's moons. It appears to hide a vast ocean of water--one substance biologists believe must be present to support life. The wanderings of the robot Sojourner over a patch of Mars added to a conviction that the Red Planet had water flowing across its surface billions of years ago and may still have water beneath its surface. Recent discoveries on Earth have shown life to be hardier than anyone suspected: Bacteria flourish in boiling springs in Yellowstone National Park, in the ice and frigid waters of lakes in Antarctica, around 250-degree thermal vents on the ocean floor and in solid rock two miles deep. Distant planets with inhospitable conditions may yet surprise us.

These findings add up to a major advance for a branch of science that didn't exist until a few decades ago. Its practitioners can't even agree on a name--it's been called exobiology, bioastronomy or astrobiology. The discipline's guiding philosophy was cobbled together in 1960 by astronomer Frank Drake, the first scientist to listen for radio signals from extraterrestrials (a notion popularized by films such as Contact). As he began his research, Drake attempted to calculate the probability that he would ever hear intelligent messages amid the static that continuously bombards Earth.

The result became known as Drake's equation. Written in scientific terms (N = R*Fp Ne Fl Fi Fc L), it appears daunting. Translated, it makes perfect sense. Drake figured that the number of detectable alien civilizations would depend on factors such as how many stars have planets, how many planets have life and how much of that life is intelligent enough to have developed interstellar communication and put it to use before losing interest or destroying itself.

Forty years ago, when Frank Drake first worked out his equation, the only thing he could say with any certainty was how fast stars form. Taking his best shot at the other variables, he calculated that the number of planets with intelligent life capable of communicating with us falls between 1000 and 100 million. Drake needed only one.

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As Frank Drake listened for the message that would solve his equation in one full-court shot, other astronomers attempted to work through the problem step-by-step. For two decades they made no progress. That began to change in 1983. At the time, Geoff Marcy was a fellow at the Carnegie Observatories in Pasadena, California. He loved astronomy but needed a challenge to renew his childhood passion for it.

Marcy decided to tackle Drake's equation. First he would find a new planet, then he would find a planet resembling Earth. He could hardly have chosen a more quixotic project. Planets beyond our solar system are impossible to observe directly, even with a telescope as powerful as the Keck. Spotting one would be the equivalent of seeing a candle from a distance of 500 miles when it's sitting next to a billion-candlepower searchlight aimed at your face. What astronomers do instead is chart the effect that a planet's gravitational pull has on a star. For instance, our sun wobbles because of the pull of its nine planets, though the most distinct influence (by Jupiter) moves it to and fro at a rate of just 28 miles per hour. It takes some expertise to nail down star wobble so minuscule from tens of trillions of miles away.

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During the years it took them to fine-tune their instruments for the task, Marcy and Butler recorded light from a sample of 120 stars. Initially they expected it would take decades of observations to determine if a star wobbled. Butler wrote a computer program to analyze the data on hand, but it was so complex it took four to five hours to process a five-minute observation of a single star. When the astronomers described their laborious techniques at a conference at Harvard, they encountered laughter and some derision. It's no coincidence that virtually the entire Harvard astronomy department is on Butler's list of scientific scoundrels.

During the spring of 1995, Marcy and Butler decided to redouble their efforts. Astronomer Steve Vogt had refurbished the light-reading instruments at the Lick Observatory near San Jose, California, making them far more sensitive, and Butler had refined his software. Marcy and Butler had never been more confident that they would be the first astronomers to identify an extrasolar planet. And they would have been, but for an accidental discovery. On October 6, Swiss astronomer Michel Mayor announced that while searching for failed stars known as brown dwarfs, he and a colleague had stumbled across an odd mass orbiting the star 51 Pegasi. According to Mayor's calculations, the mass was at least half the size of Jupiter yet orbited closer to its sun than Mercury does to ours. Its year was four of our days.

Still, it was a planet. If they had known where to look. Marcy and Butler might have found it over a long weekend. They were disappointed but also thrilled. A barrier had been broken. Butler had grown up admiring scientists such as Copernicus, Kepler and Galileo, and an Italian philosopher named Giordano Bruno, who was burned at the stake in 1600, in part for asserting there might be other worlds among the stars. Now the day had come, centuries later, when those courageous thinkers were proved correct. "The universe was screaming in my head, 'There are planets out there!'" Butler recalls. He and Marcy took Mayor's discovery as a call to action. No one else had eight years of telescope observations on tape. Surely other planets--including better candidates to support life---lurked in the data.

Butler began crunching numbers around the clock. For nearly three months, nothing. Then, five days after Christmas, Marcy received a call at home from Butler: There was something Marcy had to see. Working overnight, Butler's software had charted the wobble of a star called 70 Virginis, 200 trillion miles from Earth, so clearly that there was no question what it meant. A few weeks later, the software found another planet, this one circling the star 47 Ursae Majoris. Each orbited at a respectable distance from its sun--somewhere between the distances of Mars and Jupiter from our sun in the case of 47 UMa b, and between Venus and Mercury for 70 Vir b. The latter orbit implies a surface temperature of about 185 degrees, well within the freezing and evaporation points of water, which might support life but doesn't meet the Goldilocks conditions (not too hot, not too cold) scientists hope to find. In reality, 70 Vir's planet is almost certainly, like the giant planets of our system, made mostly of gas. But what about a moon? Jupiter, Saturn and Neptune each have large moons that may be more receptive to life than are the planets they orbit.

Amid all the conjecture, Marcy had mentioned the L word--life--and nobody in the press missed it. The phones rang for months. NASA also took note: Among its projects is a series of huge telescopes that will orbit Earth and provide views thousands of times deeper into space than the celebrated Hubble can. If all goes well, these telescopes will allow astronomers to identify Earth-size planets and examine their atmospheres. NASA also has been pumping money into land-based reflectors, including a second Keck. The twin towers will help determine how many stars have large planets and whether they are anything like Jupiter or Neptune. Marcy and Butler expect planets to be common. Since the days of Copernicus, who challenged religious leaders with the heresy that Earth is not the center of the universe, scientists have operated on a principle bearing his name: Our planet is nothing special, our sun isn't unusual, the Milky Way is garden-variety. If solar systems are common, then ours must be typical.

Or maybe not. The majority of newly discovered planets are unlike anything astronomers had imagined. Several, like 51 Pegasi b, are what Marcy calls "hot Jupiters": huge gassy masses circling close to their suns. Some have egg-shaped orbits, which make their surfaces furnace-hot and then freezing cold, sometimes within days. Hot Jupiters also may form farther out and spiral in, ejecting or destroying other planets. "It appears that the largest planet in a solar system dictates whether other planets survive," Marcy says. "In our system, the bully is Jupiter, but it's sitting in a nice, well-behaved orbit 350 million miles from Earth."

These bullies appear to be so aggressive that life may not be as common as scientists had hoped. But it may be too early for such pessimism. Hot Jupiters are easy to spot. Well-adjusted Jupiters, like our own, are wallflowers. "Within the next decade or so, we'll have charted just about every planet the size of Jupiter, or maybe Neptune, around every sun within 100 light-years, or 588 trillion miles," Marcy says. Based on what astronomers have seen so far, at least five percent of stars have planets. With 100 billion stars in the Milky Way alone, life seems a reasonable bet.