By John Noble Wilford
New York Times
Two teams of astronomers have made independent observations that they say establish for the first time the existence of a planet around a star similar to the Sun.
The planet appears to be an object at least half the mass of Jupiter and is orbiting the star 51 Pegasus, only 40 light-years away from Earth.
If these sightings are borne out by further research, the discovery would have profound philosophical as well as scientific implications. It would remove any pretension that the solar system is unique. And the likelihood that there are many other planetary systems increases the chances of there being life -- perhaps intelligent life -- somewhere else in the universe.
The discoverers do not know if the Pegasus planet is a solid or gaseous body, or if it is alone or has planetary companions. They are not sure if the planet has always been in its present orbit, or if collisions with other planets and the star's gravity drew it within five million miles of its star.
They do know that its behavior is unlike anything in the solar system; being so close, it races around its star once every four days, compared with the 88-day orbit of Mercury, which at a distance of 36 million miles is the nearest planet to the Sun. Earth is 93 million miles from the Sun.
The star 51 Pegasus would look much like the Sun to an occupant of any planet it might have at a distance comparable with Earth's from the Sun. It is about eight billion years old, as against the Sun's age of five billion years.
At first, when Swiss astronomers announced their observations on Oct. 6, other scientists reacted with caution, even skepticism. They believe that extra-solar planets may be common, but many previous announced discoveries had vanished upon closer examination.
Then two American astronomers, working at the Lick Observatory near San Jose, Calif., took a look on four nights last week and confirmed the discovery.
In announcing the new detections of the planet, Dr. Geoffrey Marcy, an astronomer at San Francisco State University, said: "We've explored all sorts of alternative explanations, and we've had the greatest minds in astronomy chiming in. Nothing else explains what we see."
With these confirming detections, earlier skepticism has faded. Other astronomers were still puzzled by the apparent presence of such a massive planetary object so close to a star. They wondered if it could be a low-mass star or substellar object known as a brown dwarf, instead of a true planet. But they expressed confidence in the abilities and judgment of both research teams.
Dr. Stephen P. Maran, an astronomer at the Goddard Space Flight Center in Greenbelt, Md., said the discovery was gaining strong support among other astronomers. "This time it appears they have really found a planet," he said.
Dr. David C. Black, director of the Lunar and Planetary Institute in Houston, said: "It's an exciting discovery. The object is probably real, not something that will go away on us."
Astronomers also predicted that the discovery could be only the beginning of many others in a short time. Indeed, the weekly magazine Science News reported in its current issue the detection of another, much larger planet candidate orbiting the star GL229, about 30 light-years from Earth. (A light-year is the distance light travels in a year, or six trillion miles.)
The discovery was made at the Palomar Observatory in California by astronomers from the California Institute of Technology.
Until now, the only accepted evidence for planets beyond the solar system centered on a dead star. Three years ago, Dr. Alexander Wolszczan, a radio astronomer at Pennsylvania State University, detected two and possibly three planets orbiting not an ordinary star like the Sun, but a dense, rapidly spinning remnant of an exploded star, known as a pulsar.
Planets of a dead star, however, are almost certainly inhospitable to life. But the newly discovered planet is also, astronomers said. Being so close to its star, the planet probably spends much of its orbit inside the star's outer atmosphere. The planet's temperature probably reaches 1,800 degrees Fahrenheit. If the planet was a gaseous giant like Jupiter, some astronomers said, the heat might have long ago driven off all its hydrogen atmosphere.
Dr. Paul Butler, a researcher at the University of California at Berkeley, who worked with Marcy on the confirming observations, said: "We don't know what the object's made of. But our back-of-the-envelope calculations suggest that a Jupiter could hang on to its hydrogen under those circumstances at 51 Pegasus."
The discovery was made by Michel Mayor and Dr. Didier Queloz of the Geneva Observatory in Switzerland and reported earlier this month at a scientific conference in Florence, Italy.
The star is visible to the unaided eye in the Northern Hemisphere, but not the planet. A slight but regular wobble in the motion of 51 Pegasus betrayed the gravitational effects of a nearby massive planet.
Butler and Marcy plan to return to Lick Observatory on Friday night for 10 consecutive nights examining 51 Pegasus. They want to conduct longer observations of the wobbling motions to refine their understanding of the planet's orbit and mass and look for the possible presence of other planets in the same system.
Any substantial changes in the orbital properties of the planet could cause significant revisions in estimates of its mass. The astronomers conceded that further study could reveal an even greater mass for the planet, making it as large as or larger than Jupiter.
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