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Earthlike solar system found

Discovery brings astronomers a step closer to determining whether we're alone.

©Los Angeles Times
June 14, 2002

Astronomers scouring the skies for planets where life might exist announced a major breakthrough Thursday -- the discovery of another solar system similar to our own.

"One of the big questions in science is, "Are we alone?' " said Anne Kinney, who directs the astronomy and physics division at the National Aeronautics and Space Administration headquarters. This "brings us one step closer to answering that."

While scientists did not find an Earth, they found a close cousin: a Jupiter. It is the first planet scientists have found with a roughly circular orbit that is a healthy distance from its star, like many of Earth's neighbors.

"It's got the smell of our own solar system," said Geoff Marcy, the University of California, Berkeley, astronomer who leads the planet hunting team. "In a sense this solar system is a missing link."

Since the first extrasolar planet was discovered seven years ago, 91 have been discovered. But many have been so odd -- many times the size of Jupiter, so close to their suns they would be permanently scorched or on wild, elliptical orbits -- scientists began to wonder if our home solar system was unique. It looks like it is not.

The planet, a gas giant known as "55 Cnc d," circles around the star 55 Cancri (pronounced KAN-kree), located about 41 light years from Earth. The middle-aged star is about the same size as our sun and is visible to the naked eye.

The new planet is about four times the size of Jupiter and is about the same distance from its sun as Jupiter is from ours. While that planet looks comfortingly familiar, the solar system also contains some strange elements: two other large planets hundreds of times larger than Earth that circle very close to the sun.

Those oddities carry the "wacky stink of some of the strange solar systems we've been finding over the past few years," Marcy said. They underscore that while Earth's orderly solar system is no longer unique, neither is it the norm.

Finding planets is difficult work. They are not visible, even to the powerful Hubble Space Telescope, because they give off only a faint glow of reflected light, light that is imperceptible in the glare coming from the stars they circle.

Instead, Marcy's team detects planets using a sensitive technique that measures the slight wobble of stars caused by the gravitational yank of stars circling them.

The technique has a bias that explains why most findings so far have been of big, close-in planets -- "oddballs" that are easiest to find because they perturb their stars the most. The smallest planet discovered so far, one of 14 others also announced Thursday, is about half the size of Saturn or 40 times the size of Earth.

Planets the size of Earth would not be visible. For example, if the team looked at our own solar system from afar with their technique, they could detect only the two largest planets, Jupiter and Saturn.

The reason many of the early discoveries have been of planets close to stars is because their full orbits take only days. The wobbles caused by the planets cannot be analyzed until at least one full orbit has been made. A planet further away, that takes years to orbit its star, takes years of monitoring to detect.

The newly discovered, Jupiter-like planet took 13 years to orbit the sun, and therefore took 13 years to detect.

"There's a tremendous amount of persistence required for this work," said Alycia Weinberger, an astronomer at the Carnegie Institution of Washington who was not involved in the research. "It's an experiment that doesn't necessarily give its most exciting results right away."

Astronomers are debating whether a smaller planet could exist in a temperate zone sandwiched between 55 Cancri's three Jupiter-like planets.

The outer Jupiter might serve, as our own does, to absorb the blows of comets and asteroids that could otherwise explode into our planet and wipe out life.

Marcy and Paul Butler, an astronomer at the Carnegie Institution of Washington, have spent 17 years perfecting the process of planet hunting and waited nearly a decade before finding their first planet.

Now, their system works so smoothly, "we're actually drowning in planets," Marcy said. Last week, the team had planned to announce 13 new planets at their news conference. They found two more over the weekend.

Given the length of time they have been monitoring some stars, they expect to find more and more "normal" planets in these distant regions from their suns that have never been probed.

"We're entering virgin territory," Butler said.

The team plans to census the 2,000 stars within 150 light years from Earth in an attempt to see how common our solar system is. "Are we one in a hundred? One in a thousand? We have no idea right now," Butler said.

* * *

SPACEWALK: In a seven-hour spacewalk, two astronauts successfully performed wrist surgery Thursday on the international space station's 58-foot robot arm, replacing an arthritic joint. One of the three wrist joints in the Canadian-built high-tech construction crane seized up in March.

-- Information from the Associated Press was used in this report.

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