(2 of 7)
If so, it may not be long before we find out. Energized by the latest discoveries, astronomers are racing back to their telescopes for more observations and to their computers to analyze years' worth of data still sitting in their disk drives. Everyone wants to be the next to find a distant world. The scientists are eagerly awaiting the results from the Infrared Space Observatory (ISO), a newly orbiting European satellite that can detect the faint heat from distant planets. They're looking forward to the 1997 installation of a new infrared camera on the Hubble Space Telescope, which could take a picture of at least one of the newly discovered worlds.
Most promising of all, they're buoyed by a newly unveiled NASA initiative, known as the Origins project, that will build a generation of space telescopes to search for new worlds. Says NASA administrator Daniel Goldin: "We are restructuring the agency to focus on our customer, the American people." And the public excitement about this field, he says, "is beyond belief."
It shouldn't be. Man's fascination with other worlds is as old as Western civilization. Galileo's discovery that they actually existed--that at least some of the pinpoints of light that wandered throughout the night sky had mountains and moons--set off a centuries-long quest to discover new planets. The first great success came in 1781, when William Herschel found Uranus. Then came the discovery of Neptune by Johann Galle in 1846. Eventually, the notion of otherworldly life made the transition out of the pages of philosophy and fiction: in 1894, the wealthy astronomer Percival Lowell built his own observatory in Arizona to try to detect the life he believed existed on Mars. He never found it, but in 1930 Clyde Tombaugh, then an assistant at Lowell Observatory and now a professor emeritus at New Mexico State University, found Pluto. It was the last planet that would be discovered until the 1990s.
Not that astronomers ever stopped looking--at first, within the solar system, for the mysterious Planet X (now considered very unlikely to exist), and then, as powerful instruments like the 200-in. Hale telescope came online, around other stars as well. But picking out a planet against the glare of a star is like trying to spot a 100-watt light bulb next to a 100-billion-watt searchlight. Astronomers find it much easier to look for the subtle influence a planet might have on its parent star.
An orbiting world's gravity should, for example, tug faintly on the star that is its sun, pulling it first this way, then that. If the plane of the planet's orbit is such that a star is being pulled first toward and then away from the Earth, the motion will cause light waves coming from the star to be squeezed together, then stretched apart--making the light look first a little bit bluer than it really is, then a little bit redder, then bluer again, and so on. These subtle color changes--examples of the so-called Doppler shift--can be precisely measured, and the magnitude of the wobble pinned down, with a device called a spectrometer.