A high-flying telescope has detected the strongest evidence yet that water - the essential ingredient for any life we know - exists on a giant gassy planet orbiting a far-away star.

It's highly unlikely that such a huge and massive object - a planet larger even than Jupiter - could be home for anything alive, but it does increase astronomers' confidence that life is just waiting to be detected on smaller, rocky planets in what are called habitable zones around distant suns like ours.

A report on the new discovery is published today in the journal Nature by scientists who monitor images and data sent to Earth from NASA's Spitzer Space Telescope, which has been in orbit around the sun for the past five years.

A team of astronomers, including Carl J. Grillmair of Caltech's Spitzer Science Center and David Charbonneau of the Harvard-Smithsonian Center for Astrophysics, confirmed in their report what other observations had suggested - that the brightly shining planet 63 light-years from Earth indeed holds abundant water vapor - on Earth we call it steam.

That's not surprising. Measurements show that this huge planet is brilliantly hot - with a temperature of more than 1,700 degrees Fahrenheit. The Spitzer telescope "sees" objects in the infrared frequencies, and the scientists confirmed the presence of water vapor on the planet by analyzing those frequencies.

The planet is one of more than 300 "extrasolar" planets that have been discovered since astronomers found the first one in 1995, and now astronomers are excited that it contains water.

"These new observations bear witness to the robust nature of water in the universe," Geoffrey Marcy of UC Berkeley, a pioneer in this worldwide, planet-hunting community, said in an e-mail. "Who could doubt that on a gentler, lukewarm planet, water would also likely exist and serve as a cocktail mixer for life."

Debra Fischer of San Francisco State, who hunts for extrasolar planets from her telescope base at Lick Observatory atop Mount Hamilton near San Jose, called the finding of water "a fantastic discovery - a training ground for ultimately detecting water on rocky planets."

Fischer noted that water is a "great solvent for carbon-based chemistry" - the kind of chemistry that results in everything alive on Earth. So, she said, that same chemistry may well be playing an identical role out there on smaller rocky extrasolar planets yet to be found.

The giant, gas planet, its surface largely composed of hydrogen and helium, is known only by its astronomical number, HD189733b. It orbits a sunlike star in the constellation Vulpecula, the fox, and for stargazers it lies in the same region where the familiar stars named Deneb, Vega and Altair shine.

Scientists who track the Hubble Space Telescope reported Wednesday that Hubble, too, has at least tentatively detected evidence on HD189733b that both carbon dioxide and methane also exist, and if confirmed, it would mean the existence of two more chemical compounds important for life on any Earth-like planet.

"This is exciting because Hubble is allowing us to see molecules that probe the conditions, the chemistry and the composition of atmospheres on other planets," said team leader Mark Swain of NASA's Jet Propulsion Laboratory in Pasadena.

In a commentary on the Nature report, astronomer Drake Deming of NASA's Goddard Space Flight Center said in the journal that among the closest stars in our cosmic neighborhood are thousands of smaller ones known as red dwarfs and that many "super-earths" detectable by ground-based telescopes seem to be orbiting them.

"Orbiting a red dwarf, this habitable super-earth may be a bizarre and unfamiliar world, hosting 'life as we don't know it,' " Deming said.