FOR the first time in human history, scientists on Earth have peered across the vast sweep of interstellar space and detected alien planets that may be capable of supporting liquid water - and thus perhaps organic life as we know it.
The dramatic discovery of two planets circling two separate stars some 35 light years away opens "a gateway to a new era," says co-discoverer Geoffrey Marcy, an astronomer at San Francisco State University.
The findings confirm what astronomers have long suspected - that our solar system is not a unique accident. It supports, but does not prove, the widely held view that earthly life is not alone in the universe.
The evidence also gives a boost to the field of planetary discovery and raises fundamental philosophical and religious questions about the nature of life and the uniqueness of mankind.
The planetary findings were revealed yesterday at a meeting of the American Astronomical Society in San Antonio. Dr. Marcy said we now should have an extra twinkle in our eyes "knowing there's a reflection of our own solar system in those stars." He added that the discovery shows that planets "aren't rare after all."
His discovery with Paul Butler of the University of California at Berkeley shows planets circling two stars. One orbits the star 70 Virginis in the constellation Virgo, the other orbits 47 Ursa Major in the Big Dipper. Both stars can be seen by the naked eye, although the planets are too faint to be perceived. The stars are about 35 light years from earth - relatively close in galactic terms.
Speaking with obvious enthusiasm, Marcy told a press conference that the planet in the Big Dipper "almost smelled like the planets in our solar system."
Using the 120-inch Shane reflection telescope at the University of California Lick Observatory, Marcy and Dr. Butler detected the planets by the way they tug on the parent stars. This causes the stars to wobble slightly. The planet around 70 Virginis appears 6.5 times more massive than Jupiter. It orbits its sun every 116.7 Earth days in an elongated orbit - a path that would put it between the orbits of Mercury and Venus in our own solar system. Earth's orbit is between Venus and Mars.
The planet in the Big Dipper orbits once every 1,100 days on path that would be a little bit outside the Mars orbit. It appears to have a mass 2.3 times that of Jupiter.
Marcy noted that the surface temperatures on the plant orbiting 70 Virginis should be about 80 degrees C (176 degrees F) - "lukewarm, warmer than your body but not much."
While not a comfortable climate for humans, Marcy speculated that rain and even oceans could exist on the planet's surface. This raises "the possibility of some sort of process of evolution into amino acids and protein," he said.
Marcy's announcement comes on the heels of the discovery last October of the first planet known to be orbiting a star similar to our sun.
It's a planet with a mass somewhere between one-half to several times the mass of Jupiter. It orbits the star 51 Pegasi, 45 light years from Earth in the constellation Pegasus. It is, however, much closer to its sun than our innermost planet, Mercury. Thus, it is thought to be too hot to support organic life.
The planet also surprised astronomers with its ability to survive in an orbit so close to its parent star that its year lasts only 4.23 Earth days. Jupiter would have to be 100 times closer to the sun than it is to be in a comparable position in our solar system. Until now, planetary theory did not allow for formation and survival of such a close-in Jupiter-sized body.
But at the meeting here, Alan Boss of the Carnegie Institution in Washington, D.C. offered an explanation of how this might have happened. In his theory, the planet would have formed at a Jupiter-like distance from 51 Pegasus. Then, through interactions with the circumstellar disk of gas and dust from which planets form, the planet would lose momentum and spiral inward.
When Michel Mayor and Didier Queloz at Switzerland's Geneva Observatory reported their discovery, planet-hunting astronomers predicted it would be the first of many planet sightings. Rapidly improving detection technology would open the way for other such discoveries, they said.
Yesterday's announcement adds credence to that prediction.
Locating planets by their gravitational tug on their parent stars has been the best technique up to now. However, astronomers would like to detect the planets directly. The latest finds should be a fillip for a new class of radio-astronomy observatories that promise even greater detection capabilities.
Robert Brown of the National Radio Astronomy Observatory (NARO) at Socorro, N.M., says that "with instruments planned by 2005, we could detect planets the size of Jupiter around a solar-type star out to a distance of 100 light years. That means that we could survey approximately 2,000 stars."