Scientists find six planets outside solar system...11/29/99

WASHINGTON (Reuters) - Six jumbo-sized planets have been detected orbiting stars outside our solar system, and five of the newly discovered objects are just the right distance from their suns to support life, astronomers said Monday.

The discoveries, made with the massive Keck I Telescope in Hawaii, were a great leap for planet hunters, who have identified a total of 28 so-called extrasolar planets in the last five years.

The recently found planets orbit stars that are about as big, bright and old as the Earth's sun, and the planets range in size from slightly smaller to several times larger than Jupiter -- the largest planet in our solar system.

They are probably made of the same inhospitable stuff as Jupiter, the scientists said: hydrogen and helium gas.

But five of them are squarely in what astronomers call the habitable zone, which could allow the existence of liquid water -- a prerequisite for life. This makes them different from most of the extrasolar planets found before this.

"These (five) planets are just the right distance, with temperatures in one case around 108 degrees Fahrenheit -- like a hot day in Sacramento," Steven Vogt, an astronomy professor at the University of California-Santa Cruz, said in a statement.

Besides Vogt, the discovery team also included Geoffrey Marcy of the University of California-Berkeley, Paul Butler of the Carnegie Institution of Washington D.C. and Kevin Apps of the University of Sussex in England. Their findings will be published in the Astrophysical Journal.

One of the planets, HD 192263, was also recently detected by a team in Geneva, Switzerland, the U.S. team said.

These scientists did not actually see the new planets, but detected their presence by watching for a telltale wobble in the stars they orbit; the wobble is caused by the gravitational pull the planets exert on the star.

No Earth-like planets are likely to be contained in these new planetary systems, Vogt said. Jupiter-sized planets in oval-shaped or eccentric orbits -- instead of the neatly stacked, circular orbits of our solar system -- would have such gravitational force as to quickly eject any Earth-type planet, he said.

But he said if these big Jupiter-sized planets are like the giant in our solar system, they may have numerous moons orbiting them.

"For a planet in the habitable zone of its star, such moons offer the possibility of liquid water and the eventual emergence of life," Vogt said.