Scientists: New Planet System Looks a Lot Like Home

Thu Jun 13, 3:57 PM ET

By Deborah Zabarenko

WASHINGTON (Reuters) - After 15 years of searching, astronomers said on Thursday they have found an alien planetary system that reminds them a lot of home.

This is the first time planet-hunters have detected what they believe is a Jupiter-like gas ball orbiting a star much like our Sun, at a distance that allows for the possibility of an unseen Earth-type planet orbiting in between.

In the last decade and a half, scientists have found more than 90 so-called extrasolar planets around stars outside our solar system. But none of these earlier discoveries has held the same potential to answer an essential question: Might there be other Earths in the universe?

"We have a (planetary) system that is maybe not a sibling of the solar system ... it might be more accurately classified as a first cousin," Paul Butler of the Carnegie Institution of Washington told reporters at NASA ( news - web sites) headquarters.

Butler and fellow planet-hunter Geoffrey Marcy of the University of California-Berkeley noted that the newly discovered Jupiter-type planet is the third thought to orbit 55 Cancri, a star in the constellation Cancer that can be seen without telescopes or even binoculars.

It is about as old -- 5 billion years or so -- and about the same size as our Sun.

Aside from its known planets, the new planetary system has a tantalizing gap between the new Jovian discovery and two other big gas planets orbiting very close to the star, Marcy said.

ROOM FOR UNSEEN EARTH?

"There's a huge region centered at about Earth-Sun distance, and in that gap ... an Earth-mass planet could exist ... and such a planet would be stable," he said.

"It could persist there for billions of years, so it's conceivable that this system has rocky planets like Mars, Venus or Earth and we simply can't detect them," Marcy said.

The planet-hunters shared their data with Greg Laughlin at the University of California-Santa Cruz, whose calculations showed that an Earth-sized planet could survive in a stable orbit in this gap.

Marcy and Butler pioneered the technique of detecting possible planets around other stars by examining the distinctive wobble their gravitational pull produces in the stars they orbit. None of these giant planets has been seen directly, and the presence of an Earth-like planet has never even been inferred by this method.

However, this is the first time that there has been a candidate system so similar to our own, Butler said.

At only 41 light-years from Earth, 55 Cancri and its planets are near neighbors in the Milky Way. A light-year is about 6 trillion miles, the distance light travels in a year.

This proximity means "it's plausible and quite likely that we will be able to image, to actually get a direct picture of this planet," said David Spergel, an astrophysicist at Princeton University who commented on the discovery. He said such a picture could be possible in the next 10 years.

Marcy, Butler and their team are looking for extrasolar planets around Sun-like stars at distances up to 150 light-years from Earth, and there are currently 1,200 such stars being surveyed.

Thursday's announcement culminates 15 years of observing with the 118-inch telescope at Lick Observatory in California. The research was supported by the National Aeronautics and Space Administration and the National Science Foundation ( news - web sites).

Images can be seen online at http:/ www.jpl.nasa.gov/images/newplanets.