Now There Are 10
You could almost see the collective eyeball-rolling of astronomers early this month. Researchers Michel Mayor and Didier Queloz of the Geneva Observatory in Switzerland had just announced at a science meeting in Italy that they had detected a new planet in the constellation Pegasus, orbiting a star quite like our sun. But sightings of planets far from our own solar system are to astronomy what claims of perpetual motion are to thermodynamics--regular events that scientists have to waste time disproving. They still grimace about the "planet" that disappeared between 1983 and 1984, and the math mistake that gave birth to a planet in 1991.
This time was different. As luck would have it, astronomers Geoffrey Marcy of San Francisco State University and Paul Butler of the University of California, Berkeley, had already reserved time on the Lick Observatory's three-meter telescope near San Jose. They were going to scan other stars for signs of planets but quickly changed their targets "when we heard [about the Swiss claim] through the grapevine," says Marcy. Instead, they aimed the telescope at a point in the starry winged horse 255 trillion miles away. The gamble paid off. In four nights of observations, Marcy and Butler said last week, they confirmed the Swiss claim. "We've explored all sorts of alternative explanations," said Marcy. "Nothing else explains what we see."
What they see is nothing so straightforward as the Jupiter-size planet itself, of course, this being 1990s astronomy. Instead, the team measured the radiation streaming out of one of the constellation's stars, named 51 Pegasi. Just as the frequency of a wailing ambulance changes depending on whether the siren is approaching (the pitch gets higher) or receding (it drops), so the spectrum of radio waves "Doppler shifts" if its source moves. When the astronomers found that the starlight's frequency kept shifting--first higher, then lower-they inferred that the star itself was moving, like the ambulance. Pushing 51 Pegasi around gravitationally, the astronomers conclude, is a companion planet. Other scientists, skeptical at first, have come around. "I immediately bet a bottle of fine New York state champagne against a bottle of beer that the report was wrong," says Steve Maran of NASA's Goddard Space Flight Center. Now he's planning to pay up.
If the believers are right, the unnamed body is the only one outside our own solar system to orbit a potentially life-giving star. This would be a finding of enormous importance. Every other claim of a planet beyond Pluto has collapsed, except for a 1992 observation of two or three planets around a dying star called a pulsar. Although a planet orbiting 51 Pegasi could not itself sustain life as we know it -- its four-day orbit skims the surface of the star, and thus raises the planet's temperature to 1,200 degrees Celsius -- its existence implies that planet formation is not unique. Are any planets outside our solar system habitable--or inhabited? The largest radio receiver ever dedicated to scanning the skies for ET signals goes on line next week. The $250,000 Project BETA, financed by the Planetary Society and run by Harvard University astronomer Paul Horowitz, will scan 250 million frequencies at a time for the one that ET might be broadcasting on, intentionally or not. (Radio signals from an advanced civilization would leak out.) No one's placing any bets, champagne or otherwise, on hearing a "what took you so long?" But with 51 Pegasi joining the club of planet-supporting stars, the odds just got better.