WAIKOLOA, Hawaii » A team of astronomers using the Keck Observatory has widened the window on the study of alien worlds, finding water vapor in the atmosphere of a giant planet around a distant star.

While water is seen as requirement for life as humans know it, its presence does not necessarily mean life exists.

In fact, the planet in question is forbiddingly hostile, with a mass several times that of Jupiter, no solid surface and a temperature of about 1,000 degrees Fahrenheit, scientists said Thursday. The water exists as hellishly hot steam.

Still, the finding shows what astronomers can accomplish using the Keck’s light-gathering power, adaptive optics to compensate for the blur of our atmosphere, and highly sophisticated instruments that can discern chemical fingerprints at vast distances.

"This is the sharpest spectrum ever obtained of an extrasolar planet," said Bruce Macintosh, an astronomer at Lawrence Livermore National Laboratory in California and a co-author of the study. The paper appeared online Thursday in Science Express and will be published March 22 in the journal Science.

Macintosh also announced the findings here Thursday in conjunction with the 20th anniversary of the Keck Observatory. Two dozen astronomers are convening at the oceanfront Fairmont Orchid hotel to make presentations on the science made possible by Keck.

Altogether about 140 scientists, technicians and journalists are attending the two-day event, a hotel official estimated.

The planet is one of four gas giants orbiting a star called HR 8799, 130 light-years from Earth. The authors and their collaborators discovered this planet, HR 8799C, and its three companions in 2008 and 2010.

The study, the most detailed examination yet of the atmosphere of a Jupiter-size planet beyond our solar system, strengthens the possibility one day of finding "biomarkers" — chemicals such as oxygen, ozone, carbon dioxide and methane that strongly suggest biological processes — around other worlds.

On HR 8799 planet C, the astronomers found water vapor and carbon monoxide.

In a news release, Quinn Konopaky, an astronomer at the University of Toronto, credited the Keck Observatory’s advanced instrumentation, along with groundbreaking observational and data-processing techniques. It also helps that Earth’s view of the system is perpendicular to the orbits, revealing the planets like merry-go-round ponies.

"We can directly image the planets around HR 8799 because they are all large, young and very far from their parent star," said team member Christian Marois, an astronomer at the National Research Council of Canada. "This makes the system an excellent laboratory for studying exoplanet atmospheres."

Key to the observations was an instrument called OSIRIS, a spectrograph designed to work with the Keck adaptive optics system. When the light from the planet is divided into different frequencies, distinct lines along the spectrum can show the presence or absence of various compounds.

"With this level of detail, we can compare the amount of carbon to the amount of oxygen present in the atmosphere, and this chemical mix provides clues as to how the planetary system formed," said co-author Travis Barman, an astronomer at the Lowell Observatory in Flagstaff, Ariz.

Bottom line: The planet formed in a way much like Jupiter, Saturn, Uranus and Neptune.

"The fact that the HR 8799 giant planets may have formed the same way our own giant planets did is a good sign," said Macintosh. "That same process also made the rocky planets close to the sun."

Keck is also at the forefront of the search for those rocky planets, many of them potentially Earth-like, scientists here say.