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.

Kara Platoni

Lick Observatory, near San Jose.

Related Stories: Astrobiology, planet hunting, outer space, evolution, NASA, UC Berkeley, SF State, Lick Observatory, SETI Institute, Debra Fischer, Geoff Marcy, Seth Shostak, Carl Pilcher, Automated Planet Finder, Allen Telescope Array

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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.