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The sky above the Lick Observatory is a denim blue and deepening. The sodium streetlights of San Jose, a twisty one-hour ride down Mount Hamilton, are a yellow smear in the distance. Down the road, the Astronomer's Diner has distributed brown-bag "night lunches" to all the graveyard-shift scientists before closing its doors for the evening. It's very quiet now on the mountaintop. Time for the planet hunt.

Telescope operator Kris Miller stands beneath the dome that encases Lick's three-meter lens and flips a switch to roll open a slit in the roof. He flips another switch, and giant protective petals that cover the telescope's primary mirror during the day peel back like a time-lapse image of a hothouse flower.

Nearby, in a series of basement rooms where the air smells like a battleship, all antique metal and dust, astronomer Debra Fischer is doing a last-minute inspection of the telescope's complicated optical system. The starlight that will be falling through it tonight has traveled through space for dozens, in some cases hundreds, of years, and will end its journey by being pinballed from mirror to mirror through slits and prisms until it finally hits a camera lens. Fischer adjusts a button or two here, flips on a fan there. "Okay, I think we're checked out," she says.

Fischer and Miller converge in the control room. It doesn't seem as though it's changed much since the telescope went into operation in 1959, with the exception of some flat-panel computer screens propped in front of displays of WWII-era switches and dials. Fischer, who is monitoring six screens at once, names a star she wants to see: 47 Ursa Major.

"We're on our way," Miller says, and the dome overhead revolves, grumbling, like the world's largest garage door. A bright orb swings into view on one of his screens. "That's a good one," he says, peering at the star.

"This one has a planet or two," Fischer says agreeably, as if it's no big deal.

In fact, it is a very big deal. When Fischer first came to this observatory twenty years ago on a class field trip led by a charismatic young professor named Geoff Marcy, finding planets around distant stars was thought to be impossible, a career killer, a waste of time.

Today Fischer is an astronomy professor at San Francisco State, and Marcy, who teaches at UC Berkeley, is arguably the first name in planet-hunting. Along with Paul Butler, another one of Marcy's former students, they are founding members of the world's most prolific planet-hunting team. There are 236 known exoplanets — planets outside our solar system — of which their team has discovered 137.

Like astrobiology, planet hunting is largely driven by the desire to know if we have galactic neighbors. After all, if there's life in space, it has to live somewhere. Yet instead of exploring the extremes of where life might set up shop, planet hunters instead hope to find familiar-looking terrain: little rocky planets circling temperate stars, ideally at a distance that would allow them to have liquid water.

At first, most of the planets they discovered were gas giants at least as big as Jupiter, which is nearly 318 times as massive as Earth, and more than 1,300 times its volume. Such places are unlikely to harbor any kind of life we'd recognize. Now, with refined planet-hunting techniques, astronomers are increasingly finding smaller planets; the smallest so far is about five times Earth's size. Just a few hundred feet down the path from where Fischer is working tonight, construction is nearly complete on the Automated Planet Finder, a robotic telescope that will be devoted solely to planet hunting and should be able to find objects as small as twice the size of Earth.

That's a good thing, if you'd like to believe Earth is more of an assembly line model than a freak planet that just happened to have the right size, location, composition, and orbit to support the biochemical phenomenon called life. In fact, Fischer believes that these low-mass bodies, although harder to find, will ultimately turn out to be plentiful among the nearby stars she's scrutinizing. "I bet my career that most of these stars have rocky planets," she says.

• • • •

Twenty years ago, Geoff Marcy bet his career on more or less the same thing. He was a postdoctoral fellow with the Carnegie Institute, stationed at the Mount Wilson hundred-inch telescope near Pasadena. And according to him, he stank. "I could tell I didn't have the right stuff," he says. "I was done, I was over, I was cooked. I couldn't do astronomy."

Convinced that he could do no more than kill time until his fellowship ended and he began his inevitable career change and slide into obscurity, Marcy decided that he might as well kill time while doing something really wild, like trying to find planets.

People thought this was nuts. Unlike stars, planets don't emit light. They reflect a little light from their host stars, but they are a billion times fainter. Nobody knew how to find them with an optical telescope. As Marcy puts it, "There is no way to find a firefly next to a nuclear explosion."

Then one day while standing in the shower and despairing, which Marcy says is the only way he did anything during those years, he came up with a way to find planets without seeing them. He would use the Doppler effect, the same technique a cop's radar gun uses to pinpoint your car's speed. "In my case," he says, "I was going to use the starlight to measure the speed of a star."

Here's how: Even though planets are much smaller than stars, they still exert a tiny gravitational tug on them. That tug makes the star wobble ever so slightly. If you watch a star night after night, measuring the wavelengths of light it emits, you can see a distinct pattern to the wobble that corresponds with how long it takes for the planet to orbit the star.

It was a nice idea, but science is built on evidence, of which he had none. Worse, the concept of looking for planets sounded pretty flaky. Marcy recalls, "When I would tell people, 'Gee, I'm thinking of hunting for planets,' eminent astronomers would look at me for a moment to see if I was serious and then they would look down at their shoes, their feet would kind of shuffle a little bit while they were uncomfortable, wondering if I was serious and whether they should believe me that I'm really going to look for little green men."

Nevertheless, when his fellowship was over, Marcy was offered a professorship in the Bay Area. "San Francisco State had no telescope, no computers, and no money," he says drily, "so we were in pretty good shape for planet hunting." He recalls that his budget for his first year was $900. "I didn't want to embarrass myself by asking for regular funding to search for planets, because you might as well ask the National Science Foundation to investigate pyramid power."

What SF State did have was an eager grad student named Paul Butler, who made a major contribution to Marcy's idea. In addition to measuring changes in the wavelengths of light emitted by a star as it wobbled toward and away from the Earth, they would create a baseline against which to track the changes. Butler's idea was to attach a cell of warm iodine gas to the telescope's optical system. The immobile cell has an unchanging chemical spectrum, and by superimposing its stable spectral image onto the star's changing one, you can measure stellar movements in fine detail.

It wasn't quite as easy as it sounded. "For eight years, from 1987 to 1995, Paul and I worked every day of the week," Marcy says. "We would work evenings. We would quit at 10 p.m. I wasn't married, Paul wasn't married, we didn't have any kids. All we did was work on developing this technique. For eight years until 1995 we found nothing. Not a single planet."

• • • •

Had this been a cheesy movie, this would have to be the obligatory montage scene: Marcy and Butler slaving away, stealing all the telescope time they could at Lick, refusing to give up. And then, just before the audience ran out of popcorn, the two would finally discover the first known exoplanet and be carried in triumph through the streets in an impromptu tickertape parade.

In reality, someone beat them to it. In 1995, a team from the University of Geneva came out of nowhere to announce that they'd discovered a planet orbiting the star 51 Pegasi. Convinced it was a mistake, Marcy and Butler spent the next four nights at Lick trying to debunk the claim. Instead, they confirmed it.

The ensuing media uproar, which many credit with helping renew public interest in life in space, and ensure NASA funding for astrobiology, only grew louder when Marcy and Butler proceeded to crank out evidence of ten more planets. For the previous eight years, they'd been so focused on honing their technique — and so unaware they had competitors — that they hadn't actually analyzed much of their data. A lot of it was sitting, unexamined, on hard disk. After 51 Pegasi, they finally combed through the data, finding proof of two more planets — around 70 Virginis and 47 Ursa Major — in a single month.

Others followed quickly after that, and the media couldn't get enough. Marcy did interviews on every television network and with nearly every talking head. "Every day there was another camera crew or two coming through, and they would often sit here all day, because some times we would discover planets while they were filming," he recalls.

In 1999, the team had another victory. By then Marcy was teaching at Cal, and he asked Fischer, then a postdoc, to model what was going on around a star called Upsilon Andromedae. Marcy and Butler had already discovered a Jupiterlike planet orbiting it roughly every five days, but they suspected there might be a second one. Try as she might, though, Fischer couldn't plot the orbital period for the second planet — there was some background noise in the data, and the numbers just weren't working out. On a hunch, she separated out the background noise, and discovered that it represented the movement of yet a third planet. And there it was: the first multiplanet solar system other than our own.

Today 23 stars are known to have multiplanet systems, Marcy says. There's reason to believe there are many more — that in fact, many of the stars that seem to have a single gas giant orbiting them actually contain multiple smaller planets that haven't been detected yet.

One reason, Fischer says, is that computer models show that as many planets as gravity will allow are packed into our own solar system. Each planet is surrounded by its own gravitational "personal space," and these are pressed up against each other. Try to squeeze another in, and the whole system falls apart, with planets booting each other out of orbit. So knowing that our own solar system is nearly "gravitationally saturated," she says, "What do we think when we see a star that has a Jupiter out here that we can detect, but nothing else? What I would think is that there is something out there, and the something else is stuff that's really interesting — it's the stuff that we can't detect yet." In other words, small rocky planets like our own.

• • • •

Of course, it takes more than rocks of a certain size to make a planet that can support life. Two years ago, the Berkeley team had discovered a Neptune-size planet circling the star Gliese 436. This May a Belgian astronomer at the University of Liège announced that he had observed it crossing in front of its host star, creating a tiny eclipse. It had dimmed the star's light a fraction of a percent, enough to provide a crucial new measurement: the planet's diameter, and therefore its density (scientists already knew its mass). Although the planet, dubbed Gliese 436b, is 22 times Earth's size, Marcy says, "We know the density of this planet to be about 40 percent of the density of Earth. The Earth is pure rock, so this planet is rock with something a little less dense than rock. Almost certainly what that substance is is water." In fact, astronomers estimate that Gliese 436b is about half water.

The first rocky planet with proof of water is a huge deal since, as far as we know, biochemistry can't happen without it. In fact, NASA's dictum in searching for life is "Follow the water."

Might this planet be habitable? It's hard to say. Its water is likely to exist in an unusual form — mostly vapor at the surface, and, toward the interior of the planet, so crushed by its own pressure that it forms a crystalline solid, a sort of "hot ice." Marcy speculates that Gliese 436b is probably so covered in water that there are no continents, therefore no place for land-dwelling life.

The bigger stumbling block is temperature. The ne plus ultra of planet hunting would be to find a water-bearing planet in the "habitable zone," an orbital sweet spot the right distance from the host star to permit liquid water. (It's also sometimes called the "Goldilocks zone," because it's not too hot, and not too cold.) Gliese 436b is too close to its host star, which is why its surface water is likely superheated steam.

Yet given how common rocky planets are believed to be, Marcy says, it's only a matter of time before researchers start finding them in the sweet spot. "Within our Milky Way galaxy alone I estimate that there are fifty billion rocky planets," he says. "A tenth of them are lukewarm in the Goldilocks habitable zone. That makes something like five billion water-laden rocky planets — five billion just within our Milky Way galaxy alone!"

Here's the kicker, he says: "My guess is that biochemistry springs up on all of them. The amino acids combine into proteins, the proteins eventually coordinate themselves into replicating molecules ... they are able to use up energy and resources, and voilà, you have life. My guess is there is life on billions of planets just within our Milky Way galaxy alone. Primitive life, maybe single-celled life and no more."

Complex life, Marcy says, probably arises less frequently, but still has fantastic odds of being out there. "Our universe as a whole has hundreds of billions of galaxies, most of which are more or less like our Milky Way galaxy with its five billion Earthlike planets," he says, "so there's an uncountable number of habitable worlds with liquid water, with continents, lakes, oceans, ponds, waterfalls, and no doubt fishlike species that spawn upstream, albeit around a star that's in the Andromeda galaxy or some such. It sounds science fiction-y, but how can it not be with all of the trillions, billions of billions of Earths out there? Billions of billions. Some of those Earths are going to make salmon, elk, cheetahs, and symphony-writing critters."

But then he brings up a worrisome problem. If the universe is teeming with life, and some of it is intelligent enough to write symphonies, why hasn't it ever called to say hello?

• • • •

Seth Shostak has long been waiting for that celestial phone call. He's the senior astronomer at Mountain View's SETI Institute, which stands for the Search for Extraterrestrial Intelligence. Since 1960, SETI has been using giant antennae to sweep the sky for transmissions from other worlds.

We Earth folks transmit all the time, albeit accidentally, sending radio, television, and military radar signals out into space. Other intelligent beings might not be able to interpret any of it, but to them our broadcasts should seem distinct from anything in nature — they have deliberate patterns, and show up only at certain spots on the frequency dial. If alien transmissions are out there, Shostak says, we can find them the same way.

After all, the fact that our civilization is only recently technological doesn't mean everybody else's has to be. "We've had radio for a hundred years, but the galaxy is three times as old as the Earth," Shostak says. "There are going to be plenty of planets out there that are several times as old as Earth, so there could be societies out there that in principle could be billions of years ahead of us. For them to build a transmitter and ping our planet might be just a high-school science fair project."

So far, that alien science project hasn't won any prizes. But Shostak points out that SETI has always had to borrow time on others' equipment, so the search has been painstakingly slow. He expects that to change this fall when its new Allen Telescope Array plugs in the first 42 of 350 planned antennas. These will be devoted entirely to SETI and will collect data round the clock, dramatically speeding up the search. Over the past 47 years, SETI has examined 750 star systems. In the next two dozen years, Shostak expects to examine one million.

In a way, searching for proof of intelligent beings in space is a bit like searching for Earthlike planets: It's betting on the odds that in a universe this vast, anything that happened once could happen again.

There is, in fact, a famous math formula that attempts to describe the likelihood of detectable intelligent life existing in the Milky Way. To use the Drake Equation, you multiply a long list of factors, including the number of suitable stars in the galaxy, the presumed number of habitable planets, the fraction of them on which life theoretically forms, and the chances that that life developed communications equipment.

But few of the variables in the Drake Equation have fixed values, so everyone who uses it comes up with a different estimate of how crowded our galactic neighborhood is. Its inventor, radio astronomer and SETI founder Frank Drake, estimated that ten thousand other intelligent, communicating species exist in the Milky Way. Astronomer and pop-culture icon Carl Sagan thought it was more like a million. Geoff Marcy thinks it's just one, and it's us.

Forget all of the other uncertainties that stand in the way of producing life, he says — not just having the right star and the right planet and the right chemicals, and not just making sure that fledgling life survives ice ages and meteor impacts and all the other cataclysms that could befall a young planet. Even if you manage to produce an intelligent society, he asks, how long does it last? Nobody knows, but Marcy suspects the window might be very short. "When a species becomes technological, as we have within a few hundreds of years, they develop weapons, they develop toxins, they develop ways to ruin their environment, they tinker and they make a mistake," he says. "How long do you throw the dice?"

In the end, he thinks, each galaxy may be capable of producing multiple intelligent species that will never coexist; they'll be like a chain of lights on a Christmas tree, each one winking on as another winks off. Even if there's another intelligent species in the galaxy next door, Marcy says, we'll never hear from them because they're too far away.

Shostak thinks this is overly pessimistic, although he certainly agrees there may be a synchronicity problem, in which not all intelligent species are at the broadcasting stages of their existence at the same time. "Earth has had life for somewhere between 3.5 and 4 billion years, and how much of that time did it have life that could build a radio transmitter? The last couple decades," he says. "So you can be sure that if there's lots of life out there that most of it is not building the kind of technology we could find."

But all of these doubts, Shostak points out, can be settled by finding just one positive signal. "For five hundred years, astronomers have been telling us we're not that special," he says. "We used to think the Earth was the center of the universe. That's pretty special. Well, it turns out it's not."

Neither did our solar system turn out to be the only one, and it seems increasingly likely that Earth isn't the only pale-blue dot with all of the ingredients for life. "There's a lesson in all of this," Shostak says. "We keep thinking that there is something special about our location, our situation, something, and that's perfectly natural to think that, but the track record is that sort of assumption is going to be wrong."

So if we do find life in the universe, especially if we find it twice in our own solar system as astrobiologists have been endeavoring to do, what does that tell us? "That life is just part of the universe in the same way that asteroids are part of the universe," Shostak says. "Life's not a miracle. Life is just an infection. It's everywhere. It's just one of those things."

• • • •

That search for just one positive signal still has a long way to go, and now scientists are going to have to do it with significantly fewer resources. The budget for NASA's Astrobiology Institute was slashed last year from around $62 million a year down to roughly $31 million this fiscal year and next.

The Jupiter Icy Moons Orbiter, which was supposed to give astrobiologists a close-up look at the moon Europa, a likely candidate to host life within our own solar system, was scrapped. Two long-awaited telescope probes of great value to planet hunters — the Terrestrial Planet Finder and a craft called SIM PlanetQuest — met a similar fate.

Instead, NASA says its priority will be returning a manned mission to the Moon, and later landing people on Mars. Academic scientists, who are less dependent on NASA for their projects and funding, will tell you plainly that they believe the space agency is mainly pursuing a public-relations mission, and that any research opportunities have been tacked on as an afterthought. "The goal of going to the Moon and Mars is not science-driven," Fischer says flatly. "It's very politicized."

"What's the point of going to the Moon and Mars if you don't do the science?" Shostak agrees. "Are we just doing it for the tourism?"

Depending on whom you ask, the motivation is either to pursue a space race with China (which announced in 2003 that it was planning lunar missions), to stir up the sort of national pride inspired by the United States' first Moon landing, or to reaffirm NASA's image as a manned space agency despite two shuttle disasters and the lackluster Space Station program.

Admittedly, Shostak says, the public is hungry for something new and glorious. "We're always spending all this money to see astronauts play with their food in zero-G orbit around the Earth," he says. "They've been doing that for decades now. Where is the excitement, where is the goal, where is the really inspirational effort? Going to Mars, well, there is something romantic about that."

Not to mention dangerous and expensive, two more reasons some scientists say this is a bad time for manned space exploration. With Iraq draining vast sums from the federal budget, and NASA overburdened with the shuttles and the Space Station, they say it makes no sense to launch large, costly rockets that can transport humans when robotic probes are so much cheaper. Plus, when robot probes fail — and Mars missions have a history of failure — nobody dies or taints the very surface astrobiologists hope isn't already contaminated with Earth life from previous landings.

Carl Pilcher, director of NASA's Astrobiology Institute, doesn't know if the budget cuts will be permanent, but points out that $3 million of missing funds was restored this year, bringing the total up to $34 million. "My crystal ball is cloudy, but I'm an optimist," he says. "We are trying to do things that are so exciting and so compelling that they will lead to the restoration of funding." He has a point: It was the later-discredited announcement that traces of life had been found in a Mars meteorite that stirred up public excitement and prompted NASA to start an astrobiology institute in the first place.

But Pilcher also warns that when funding goes on hiatus, the field risks losing the talented young scientists it attracted during the previous decade: "It's a great concern, because it introduces uncertainty in their prospects." Likewise, Fischer agrees, when spacecraft missions are scrapped — or in NASA parlance, "pushed back" indefinitely — they lose the engineering team that designed them. Even if the mission gets rescheduled later, the brainpower that created these complex machines has dispersed to other projects. "Scientists are caught in this — if they wanted us to be at each other's throats, they couldn't have planned it any better, because my best friend's mission is canceled and my mission goes forward," Fischer says. "Now he goes and lobbies and his mission gets put back on the books and my mission is canceled. It's just horrible. And they're all valuable, is the truth, and they all worked, and it's just that things got too expensive."

The cutbacks won't affect some of the new projects expected to ramp up this fall, like the Automated Planet Finder at Lick and the largely privately funded Allen Telescope Array. But for Geoff Marcy, it's unbearable to have any projects sidelined on the cusp of such an era of discovery. "We have a chance to be the Niña, Pinta, and Santa Maria in a cosmic sense," he says. Okay, he concedes, Columbus didn't have to sail for the New World when he did; some other guy could have done it a hundred years later. Still, it breaks Marcy's heart not to have as many crafts as possible out there sailing the interstellar blue, looking for land.

"All I can say is that we humans began two million years ago on the East African savanna with sticks and stones, and miraculously, in a mere two million years, a blink of an eye on the geological timescale of things, we humans have developed computers and piano concertos and rocket ships and huge telescopes," he says. "In those two million years we all have asked ourselves, are there other Earths, are there other life forms out there, are we alone? We're the first ones to have a chance to answer this ancient human question. And we're blowing it."