New Planet: Large And Luminous

Astronomers have discovered a planet bigger than Jupiter, just 15 light-years from Earth, apparently a huge ball of gas with a surface temperature well below zero.

Geoffrey Marcy, who heads a four-member team of San Francisco State researchers, announced the discovery the week of June 22 at a scientific symposium in Canada. The finding was confirmed by a separate team in Switzerland.

The group found the planet using the Keck I telescope in Hawaii.

Its huge mass - at least 1.9 times bigger than Jupiter's - was detected by a wobble in the motion of a nearby star, not by direct visualization.

There is no evidence of any solid land on the planet on which Earth-like life forms might have developed. Scientists say the planet is mostly hydrogen and helium with a surface temperature of about 80 degrees below zero.

The planet was the first to be found orbiting a small star called Gliese 876, one-third the size of the sun. It is one of the closest members of a class of low-mass stars that are the most common in the Milky Way galaxy.

The previously closest-known "extrasolar" planet orbits a star about 35 light-years away. A light-year is 5.9 trillion miles, the distance light travels in one year.

"It's not spitting distance, exactly, but spacecraft distance perhaps for future generations," Marcy said Wednesday.

Marcy added that the discovery of a planet around Gliese 876 dramatically raises the odds that many more planets may be found relatively close to our own solar system.

"The key issue is that this is by far the lowest-mass star around which a planet has ever been discovered," he said.

Twelve such planets have been discovered by the world's astronomers, including seven by Marcy and his associates in the past three years. A report on the most recent discovery will be published in the June 27 issue of Science News.