By Deborah Zabarenko
Reuters

WASHINGTON (June 13) - After 15 years of searching, astronomers said 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 rocky 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 planets like Earth 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 headquarters.

This ''cousin'' was one of 15 extrasolar planets whose discovery was announced Thursday by the 
planet-hunters.

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 from Earth without telescopes or even binoculars.

It is about as old -- 5 billion years or so -- and about the same size as our Sun. The newly discovered 
planet moves in an orbit similar to Jupiter's, rather than the elongated, eccentric orbits that are 
more typical of extrasolar planets.

Aside from its known planets, the new 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 AN 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 a distance of 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 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.

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

Copyright 2002 Reuters Limited.