Other Worlds

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"When I look at the stars at night and see stars like ours, to me that means billions of opportunities for life," says Debra Fischer, in a firm, gentle voice.

Sweet-faced and brown-eyed, Fischer has been called a planet hunter, a term she finds lacking. She prefers the old-fashioned moniker: astronomer. She is, indisputably, a planet finder.

At Lick Observatory in California, the UC Berkeley researcher monitors 300 stars for suspicious behavior that would betray nearby planets. Her teammates in Hawaii and Australia track 600 more. A Swiss team, the first earthlings to detect a foreign planet, keeps tabs on 1,000.

Peculiar, super-sized planets are popping up all over.

Most of the 30 new planets found since 1995 are "only children." The star Upsilon Andromedae has a brood of three. And at least two other stars hint at sheltering a pair. But to say that these small families of mammoth planets represent normalcy is akin to casting a tuna net into the ocean, and then declaring that all fish are large. The holes in the planet-nets of Fischer and her colleagues are simply too big to catch small planets.

"Right now, we couldn't detect our own Jupiter," she says. "We're never going to find an Earth-sized planet."

The net is actually a web of mathematics and astronomical observations. Although a Scottish astronomer now claims to have detected actual starlight reflecting off the surface of a planet, these new worlds are generally too dim to be anything like visible.

But their effect on their parent stars is, mathematically, detectable. Our sun exhibits the same suspicious behavior that the planet finders hope for.

If it were unburdened by planets, our sun would spin in one spot, like a perfectly balanced top. Instead, like a dog on a short chain, the sun traces small "circles" in space. It is tugged off center as it follows the gravitational pull of enormous Jupiter. If you stood on one of Fischer's fat planets and looked back at our solar system, you would not see Jupiter. But the sun would appear to creep right, then backward, then left, and then forward, in concert with Jupiter's 12-year orbit.

Astronomers would analyze the sunlight for the tiniest shifts in its wavelength, wrought by the sun's backward-forward motion. The degree of wavelength-shift would indicate the speed with which the sun was chasing a planet. That, in turn, would reveal the planet's size. The duration of one backward-forward cycle would equal the duration of that planet's orbit.

So far, the planets caught in the mathematical net are a strange bunch. They are giants, in the size range of Jupiter, which weighs 300 times more than the Earth. And they are probably gaseous, like Jupiter. Their orbits, however, are utterly foreign.

A dozen of these giants orbit 10 times closer to their stars than Earth orbits the sun. And the closer a planet orbits, the faster it travels.

One of these star-huggers, which was recently observed (mathematically) crossing the face of its star, celebrates a new year every three and a half days.

The rest of the giants adopt oddly elliptical orbits. The planets in our own solar system, by contrast, pursue near-circular paths. It may be that ours represents the rare, happy family.

"These planets are probably born on a circular orbit," Fischer says, "and then something perturbs them." The perturber might be a cruel sibling. Two planets, if they pass too closely, could find themselves doing a gravity twirl that would warp both their orbits, possibly hurling one sibling clear into space.

Or, since many stars come in pairs that orbit each other, the perturbing force could be an unseen companion star that causes the planet to reel between two centers, like a child in shared custody.

Both these orbit styles, the star-huggers and the ellipses, are bad news for people in search of far-flung clots of life.

A close orbit keeps its planet uncomfortably hot. And a planet in an elliptical orbit alternately fries when it's near the star, and freezes when it's not. Worse, both types of orbit suggest these planets may have tossed smaller siblings out of the system.

"We think these planets formed farther out, then moved in, and wiped out Earth-like planets," Fischer says. "These may be failed solar systems."

So, planets, planets everywhere, and none yet that seems amenable to sprouting grass?

"Oh, there is certainly room for simple life to evolve in these systems," Fischer protests. "Everywhere scientists look for life on Earth, they find it. They find it in sulfur vents on the ocean floor, and deep in the ice in Antarctica."

Furthermore, even if the gassy giants are sterile, recall that they are not the only planets; they're just the only planets big enough to be caught so far. And only about 5 percent of stars seem to host these fratricidal bullies.

"Eighty or 90 percent of stars might have systems like ours. We can't rule that out," says Fischer. "And these large planets must be hard to put together. Earths must be easier to make. They're just little piles of rubble."

Yes, just little piles of rubble, for which we yearn terribly, and for which we troll the dark galaxy, casting ingenious nets.