VANCOUVER, JUNE 18 -- Canadian astronomers said today they have detected evidence of at least two planets, two to five times the mass of Jupiter, in orbit around two stars similar to the sun within 50 light-years of Earth.
The findings could represent the first discovery of planets outside this solar system, shed new light on the origins of the Earth and give new momentum to the search for extraterrestrial life.
They come at a time when many astronomers say the field, thanks to new technology and approaches, is ripe for major discoveries.
The evidence, based on a six-year study using a new technique, is the best so far that there are planets beyond the solar system, according to Bruce Campbell, of the Dominion Astrophysical Observatory, who reported it.
But it will take long years and work by many scientists to confirm the findings, he said. "When you make an extraordinary claim, you need extraordinary evidence."
The news was presented at the first joint meeting of the American and Canadian Astronomical Societies on the campus of the University of British Columbia here. An estimated 750 astronomers are attending.
"It's tantalizing -- but inconclusive," said Frank Drake, founder of the Search for Extraterrestrial Intelligence (SETI). "You really need a 30-year program," added Drake, who is professor of astronomy at the University of California at Santa Cruz.
Planets give off no light and are difficult or impossible to detect from Earth. However, according to Drake, the Hubble space telescope -- its launch delayed by the space shuttle disaster -- could see one of the planets if it is reconfigured for that purpose.
The Canadians used a new twist on an old, inefficient technique in which astronomers measure the velocity of stars to detect slight "wobbles" in motions caused by the gravitational tug of the unseen companion -- the presumed planet.
The Canadians' method gave them from 50 to 100 times the accuracy of previous techniques, allowing them to determine speed changes within 25 miles per hour.
Of 16 stars monitored for the past six years, the team found "clear evidence" of these possible planetary companions in two. Five others showed tenative signs of such bodies, Campbell said.
The most significant case is a star called Epsilon Eridani, about 11 light-years from the sun in the constellation Eridanus (the River). Its behavior indicates a companion body from two to five times the size of Jupiter, by far the largest planet in this solar system, but only 1,000th the size of the sun, a typical star.
The other significant case is Gamma Cephei, about 48 light-years away, with a companion in orbit that is about 1.7 times the mass of Jupiter. A light-year is the distance light travels in a year, about 6 trillion miles.
The question of whether other solar systems have planets such as the sun's is one of the great unsolved mysteries, but recent developments have given rise to great optimism in the scientific community as well as some confusion.
In 1984, University of Arizona astronomers reported sighting the first planetary body outside our solar system. However, last year two other teams of astronomers reported they had failed to duplicate the findings that there was an object near the star Van Biesbroec 8. The Arizona team backed off.
Astronomers concluded in that case that either the object had moved, that a cloud of dust and gas had fooled the instruments, or that the observations were wrong.
Astronomers have suspected the existence of substars known as brown dwarfs, which might also cause a star to wobble. A brown dwarf is, in theory, an object formed out of a lump of gas whose mass is too small to ignite its nuclear fires.
Scientists are not sure what mass is required to trigger a nuclear reaction and have searched for an example of such a body, something between the stars and planets. None has been found and since the newly discovered objects appear smaller than brown dwarfs, Campbell said, the objects are probably planets.
The search for other planetary systems picked up momentum in part because of findings in 1983 by the Infrared Astronomical Satellite, indicating that the sun in this solar system is not the only star that can generate planets.
But its findings were of huge orbiting discs of matter surrounding stars that scientists theorized might be embryonic patches from which planets would evolve.
The Canadian team's findings seem to be of fully formed planets.
After making his announcement, Campbell announced his resignation from the observatory because of what he called "frustration and disappointment" over recent cutbacks in his government's funding for basic science research.