The discovery was announced at a news conference Wednesday in Washington, and the findings have been posted on the National Science Foundation’s Web site and will be published in The Astrophysical Journal.

The authors said the relative ease by which planet was found  in only 11 years  led them to believe that such planets must be common.

“Either we have just been incredibly lucky in this early detection, or we are truly on the threshold of a second Age of Discovery,” they wrote in their paper.

Pressed during the news conference about the possibility of life on Gliese 581g, Dr. Vogt protested that he was an astronomer, not a biologist. Then he relented, saying that, speaking strictly personally, he believed that “the chances of life on this planet are almost 100 percent.”

Asked the same question, Dr. Butler squirmed and said, “I like data.” After a pause he added: “And what the data say is that the planet is the right distance from the star to have water and the right mass to hold an atmosphere. What is needed simply to find lots and lots of these things is lots and lots of telescope time.”

The latest results from Gliese 581 were harvested from observations by two often competing teams, using telescopes in Chile and Hawaii to measure the slight gravitational tugs the star gets as its planets swing by.

Image Credit... Astrophyisical Journal

This is hardly the first time around the block for Gliese 581, which is a longtime favorite of planet hunters and now is known to have six planets in its retinue. It is a dwarf star about one-third the mass of the Sun and only about one-hundredth as bright, allowing planets to huddle closer to the campfire. “It hauntingly reminds us of our own solar system,” Dr. Butler said.