A telescope atop Mauna Kea on the Big Island has discovered what appears to be liquid water on a rocky planet 20 light years from Earth in the constellation Libra, astronomers announced today.

The discovery of liquid water on a planet other than Earth is an important step in the search for extraterrestrial life, the team that made the discovery said in a statement. The research was conducted from Mauna Kea’s W.M. Keck Observatory and included University of Hawaii astronomer Nader Haghighipour, who said, “By determining the orbit of this planet, we can deduce that its surface temperature is similar to that of Earth.”

The planet, called Gliese 581g, has a mass three to four times the size of Earth, and orbits its star with five other planets.

Gliese 581g’s mass indicates that it is probably a rocky planet with enough gravity to hold on to its atmosphere.

The team discovered Gliese 581g by searching for tiny changes in the star’s velocity that arise from the gravitational tugs of its planets. The team used 238 separate observations of Gliese 581 taken over a period of 11 years.

Haghighipour said that the team is keeping tabs on many nearby stars using the Keck Observatory.

“As we collect more and more data about how these stars are moving, we expect to find many more planets with potentially Earth-like conditions,” he said. He noted that to learn more about the conditions on these planets would take even bigger telescopes, such at the Thirty Meter Telescope planned for Mauna Kea.

The team is led by Steven Vogt of the University of California, Santa Cruz and Paul Butler of the Carnegie Institution of Washington. Other team members include UCSC associate research scientist Eugenio Rivera, and Gregory Henry and Michael Williamson of Tennessee State University.