U.S. astronomers have discovered a planet around a distant star that reminds them of one in our own solar system. The finding suggests that our solar system is not unique.
Since 1995, astronomers have found dozens of planets orbiting stars. But now, the team that has found most of them has detected a unique one among them. "For the first time, this is an extra-solar planet that resembles one in our own solar system," he said.
Team member Geoffrey Marcy of the University of California at Berkeley says it is a giant gas planet like Jupiter orbiting the star 55 Cancri in the constellation Cancer, relatively close to us at just 41 light years away. Not only is it roughly the same size as Jupiter, but it also has a similar, nearly circular orbit at about the same distance from its star.
"All the other planets that we've ever found around other stars orbited very close to the host star," he said. "Many of them orbited in elongated orbits. So we had never discovered a planet around another star that resembled one of planets in our own solar system."
Mr. Marcy's team detected the new Jupiter look-alike the way all the others have been found. Instead of seeing the planet directly, they inferred its existence by the wobble its gravitational pull exerts on its star.
Mr. Marcy's colleague, Paul Butler of the Carnegie Institution says the star's wobble is determined by the way its light flickers.
"We look for the colors of the star to shift back and forth. So when we see the star wobble back and forth, we know something must be orbiting it and we can work backward [to learn] what the orbit and the mass of the orbiting companion must be," he said.
They had to follow the new planet one full orbit before they could make their calculations, and that took more than 13 years.
The researchers also announced discovery of 14 other new planets, bringing the total known outside our solar system to 90. But the director of astronomy at the U.S. space agency NASA, Anne Kinney, says the one in the constellation Cancer stands out.
"The real question we've had is, is there anything like us anyplace else? Today we have no idea of what kinds of planets or solar systems live around the neighboring stars, and this tells us for the first time that at least there is one example of a solar system that looks something like ours," he said.
But it is not exactly like ours. The researchers say they also found two other big gas planets orbiting the star 55 Cancri, but much closer in. In our system, the closest planets are the smaller, rocky ones like Earth.
"We never really predicted that we would find a system like this one. It seems to me that every time we find a planetary system, it has characteristics new to us. The theory of planet formation is not mature enough for us to make good predictions," he said.
The current technology is precise enough only to detect the most massive planets. But NASA will launch telescopes to hunt smaller, rocky ones like Earth. One set for launch next year will detect them as they pass in front of their stars, thus making the star dim. Another scheduled for launch in 2015 will actually view rocky planets visually and measure their chemical signatures to see if conditions are right for life.
Princeton University astronomer David Spergel says if these instruments were available today, researchers would train them on 55 Cancri, where the new Jupiter was found.
"This would be our number one target. If one were to make a bet on where we are most likely to see the first planet like our own, it would be this system," he said.
In the meantime, Geoffrey Marcy, Paul Butler and colleagues are working their way through a catalog of 1,200 stars, expecting to find many more large planets with the characteristics of Jupiter. Mr. Butler says they began searching most of those stars only within the last half decade or so, therefore they will have to wait several years to confirm them as they complete their orbits.
"We have lots and lots of candidates, but until the orbit is completed, we can't be sure what the orbital period is and we can't be sure what the mass of the planet must be," he said.