Professors Geoff Marcy and Debra Fischer in front of the Campbell Hall rooftop observatory. Noah Berger photo.

18 October 00 | Debra Fischer is no stranger to the twinkling orbs of light dotting the Milky Way 100,000 light years into space.

Roughly 200 billion stars rest in the spiraling arms of this celestial pinwheel and at least 12 billion solar systems harbor planets, not unlike the gaseous giants and terrestrial worlds of our own planetary neighborhood.

Night after night, atop Mount Hamilton's summit near San Jose, Calif., Fischer uses a Lick Observatory telescope to scour the heavens in search of Earth-like worlds.

Fischer is advancing the immature science of planet-hunting, along with pioneering planet-hunters Geoff Marcy, an astronomer in the College of Letters and Science at Berkeley, and Paul Butler of the Carnegie Institution in Washington, D.C., with brand new observations of planets the size of Jupiter and Saturn. These are the signposts of Earth - worlds that may have given rise in the past or, perhaps, in the present to elementary forms of life.

"The rate at which we are discovering new planets in other solar systems is beginning to overtake us," said Fischer, an astrophysicist and postdoctoral fellow who works down the hall from Marcy in Campbell Hall.

"Every time we publish a paper, we've got five new discoveries lined up for the next publication," Marcy concurs, while scrolling through screens of data - celestial plots of stars and their locations - and fielding phone calls in his office, situated one floor beneath a rooftop telescope.

In the five years since the slight jitter of a distant star - 51 Peg, located in Pegasus, a constellation 40 light years away - first betrayed the presence of a planet, several astronomy teams have brought the count of worlds outside Earth's solar system to 54. As the Doppler technique for measuring the stellar motion of distant planets is perfected - now down to within plus or minus 10 feet per second, which is like measuring the motion of a star moving at the speed of a casual bicyclist 30 light years - planet-hunters are beginning to detect planets faster than they can report them. Some of them are smaller than the Jupiter-sized spheres recently observed.

In March, Butler, Marcy and Fischer discovered two planets about the size of Saturn, following the discovery more than a year before of the first triple-planet system, Upsilon Andromedae, with three gaseous worlds circling a common sun. Another breakthrough in August of this year - the team's detection of a planet crossing in front of the glare of its own sun - sent the scientific community reeling in star-studded bliss; many realized that stars are prolific planet factories and that life in some elementary form must pervade other galaxies.

Finding the Holy Grail

"This is like finding the Holy Grail in astronomy," said Marcy, who uses Hawaii's Keck Observatory telescopes for his work. "For the first time in history, we've been able to prove that there are many planets orbiting other suns and there are probably many Earth-like analogs that have liquid water and atmospheres. There's no question that there are oceans and lakes out there. No question that the universe is teeming with life."

A young science, extrasolar planet-hunting is likely to take off in the next several years. Marcy estimates there are 12 billion planetary systems in the Milky Way alone. "And that's probably on the low side," he said. The detection of more planets smaller than Saturn will add validity to the theory that planets form in dusty disks around sun-like stars, with several sibling planets.

"A common theme in nature would have it that there are probably more low-mass planets like Earth than high-mass planets like Jupiter, just as there are more grains of sand on the beach than boulders," said Fischer. "We have been limited in our ability to observe these smaller planets up until now because our techniques for detecting planets were limited."

Stars with Multiple Planets

In fact, two multi-planet systems have been detected: Upsilon Andromedae, 44 light years away in the constellation Andromeda, and HD 83443, which is 141 light years away in the constellation Vela. The Berkeley team announced its discovery of the three-planet Upsilon Andromedae a year and a half ago.

Still more fascinating are the observations of extrasolar planets almost next door to our solar system. Another team recently discovered a planet only 10.5 light years from Earth. The planet is similar to Jupiter in its distance from its star, its orbital period and its mass.

It may be a while, though, before definitive proof exists that stars commonly form with several planets. Until a telescope network that creates one huge array in space is launched in 2008, astronomers must perfect their ground-based techniques, Marcy said. By then, they are likely to have a sizeable inventory of planets around nearby stars and the engineering marvels of a giant orbiting observatory to search for water-rich worlds something like our own.