Astronomers used Mauna Kea’s Keck 1 telescope to discover an Earth-like planet that could contain water and possibly even life, a finding likely to reinvigorate the search for extraterrestrial life and inspire Hawaii’s next generation of space explorers.

Researchers in Washington, D.C., and Honolulu announced yesterday the discovery of the rocky planet called Gliese 581g some 20 light-years away, orbiting in the sweet spot close enough to its own sun — but still far enough away — in what they call "the habitable zone."

"This is the beginning of a new era," said Nader Haghighipour, an associate astronomer at the University of Hawaii who is on the research team. "The goal of extrasolar planet hunting is to find Earth-like planets in the ‘habitable zone.’ And this is the first one."

The discovery of Gliese 581g in a six-planet solar system twice as old as our own in the Libra constellation is likely to spur the imaginations of future Hawaii stargazers and scientists, said Mike Shanahan, director of education, exhibits and planetarium at the Bishop Museum.

Educators at the museum’s planetarium provide a morning "space update" to visitors six days a week and are likely to include the discovery of Gliese 581g and its possibility of water and life in the next few days, Shanahan said.

"Finding water enormously advances the chances of finding life out there in the cosmos, and that’s a giant hook in drawing the public’s interest," Shanahan said. "When you include that it was done right here in the islands, every little piece helps."

From atop the Big Island, the W.M. Keck Observatory has been staring at the red dwarf star Gliese 581 for 11 years and in 2000 found the first of six planets orbiting it, Haghighipour said.

Each planet was given a letter designation in order of discovery, starting with 581b in 2005. Some were too close to their star and, therefore, too hot to contain water. Others were too big, too gassy, or too cold.

But the last planet, Gliese 581g, was just right.

"This really is the first Goldilocks planet," Gliese 581g’s co-discoverer, R. Paul Butler of the Carnegie Institution of Washington, told reporters at a Washington press conference yesterday.

Because of the planets’ distance from Earth and their lack of light, astronomers peering through the Big Island’s Keck 1 telescope cannot actually see them — let alone find direct evidence of water, Haghighipour told the Star-Advertiser.

The planets’ existence is based on observations of Gliese 581’s wobble, indicating that planets are pulling on the star as they orbit around it, Haghighipour said.

Gliese 581g — and the solar system it flies around in — hardly resembles our own.

The planet is three to four times the mass of Earth. But the Gliese 581 star is just one-third the size of Earth’s sun. It’s also 8 billion years old compared with 4.5 billion years for the sun.

Because the Gliese 581 star generates far less radiation than Earth’s sun, planet Gliese 581g has to be much closer to its star to replicate Earth-like conditions.

While Earth spins on its axis 93 million miles from the sun, Gliese 581g sits only 14 million miles from its sun. Like Mercury, Gliese 581g likely keeps the same side toward its star, with half of the planet in perpetual darkness and the other in sunlight.

Gliese 581g takes less than 37 days to make a complete orbit around its sun, Haghighipour said, compared with 365 days for Earth.

Despite all the differences, the math adds up to suggest that Gliese 581g has the right conditions to be hard and rocky and contain water — and perhaps even life.

"We don’t have any hard evidence of water," Haghighipour said. "But this is the first planet similar to Earth — as far as size and mass — that is sitting at the right distance from its star. So we conclude that it might have liquid water."

Based on all the data, Haghighipour said the team led by Butler and Steven Vogt of the University of California, Santa Cruz, instantly recognized the ramifications for Gliese 581g, beginning a few months ago.

"Everyone on the team came to the same conclusion: It has all the right conditions, orbit, mass," Haghighipour said. "’Oh, man, this must be similar to Earth.’"

The Associated Press contributed to this report.