Astronomers searching for worlds around distant stars announced the discovery Thursday of the first solar system like Earth's, boosting hopes that there are other habitable spots in the universe.
"One of the big questions in science is, 'Are we alone?' " said Anne Kinney, who directs the astronomy and physics division at NASA 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 UC 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'd be permanently scorched or on wild, elliptical orbits--scientists began to wonder whether our home solar system was unique. Looks like it's not.
The planet, a gas giant known as "55 Cnc d," circles around the star 55 Cancri, 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 not 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 planets 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.
