BY THE TIME GEOFFREY MARCY stepped up to the microphone, his audience could barely conceal its anticipation. For days, rumors had been circulating around the American Astronomical Society meeting in San Antonio, Texas, that Marcy and his colleague Paul Butler had something big. Then he dropped his bombshell. "We're here," said Marcy, "to announce the discovery of two new planets, orbiting stars similar to the sun." It wasn't the first time such planets have been found. But what made this discovery so exciting was that at least one of the new worlds, about eight times the size of Jupiter, is temperate enough for water to exist on it in liquid form. And that raises the tantalizing possibility that it could harbor life.
Marcy and Butler's announcement could change the course of astronomy. "This is extraordinarily important," says astronomer Alan Boss of the Carnegie Institution of Washington. "This is the first glimmering we have that normal solar systems exist beyond our own." It is sure to trigger a rush to find new planets. Indeed, half a dozen teams around the world are already looking. And in an address to the astronomers a few hours after Marcy's talk, NASA administrator Daniel Goldin announced a new program whose goal, he says, will be "not only detecting but taking direct images of Earthlike worlds, right down to oceans, continents and mountains, within 25 years."
That won't be easy. The newly discovered planets are much bigger than Earth, yet it is almost impossible to learn very much about them. The stars they orbit--70 Virginis in the constellation Virgo and 47 Ursae Majoris in the Great Bear--are each about 35 light-years away. The speediest space probe would take millions of years to reach them; even a radio signal, the fastest known thing in the universe, would need 35 years to get there, and it would take another 35 for any aliens, should they exist, to answer. The planets are so dim that they cannot be detected directly. In fact, the only evidence Marcy and Butler have is observations of tiny wobbles in the positions of the two stars, caused by the planets' massive gravity. The intensity of the wobbles tells the astronomers how big each planet is, and the timing reveals how long it takes each to orbit its star.
That information, along with the laws of orbital mechanics and planetary formation, let Marcy and Butler paint a portrait of the new worlds. They're like Jupiter: mostly gas, with small cores of rock. If water exists on either, it's the temperature of hot tea and is located high in the atmosphere; creatures that live on the planets would be very different from anything on Earth. Says Marcy: "It would have to be some sort of life that evolved without ever touching the ground."
There is another, intriguing possibility, however. As Marcy points out, the planets are almost certainly orbited by one or more moons. "If they are comparable in size to the moons of Jupiter and Saturn," he says, "they could easily have rain and oceans." Such speculations fire the imagination. But the mere fact that these giant planets exist is enough for the scientists. As astronomers have learned, the discovery of one or two new heavenly objects is usually just the beginning. Marcy's team is already analyzing data from some 60 other stars. "We have hints," he says, "that there may be planets around some of these as well."