The discovery of a giant planet in a Jupiter-like orbit around a nearby star shows our solar system is no fluke.
The new planet is the first of some 90 reported around other stars that "resembles a planet in our own solar system," Geoff Marcy of the University of California at Berkeley announced on Thursday.
It takes 13 years to orbit 55 Cancri, a star 41 light years away in the constellation Cancer; Jupiter takes 11.8 years to orbit the Sun. The new planet's orbit is three times more eccentric than Jupiter's, but less eccentric than Mercury's.
Two other planets somewhat smaller than Jupiter also orbit 55 Cancri, but both are very close to the star, circling it every 14.65 and 44.3 days. The large gap between inner planets and the outer one leaves plenty of room for a terrestrial planet in an Earth-like orbit, which Greg Laughlin of the University of California at Santa Cruz calculates should be stable for billions of years.
The gap includes the habitable zone for 55 Cancri, which is close to the sun in age, mass, and brightness, and barely visible to the unaided eye in a dark sky.
Other planets discovered outside the solar system during the past six years had left astronomers wondering if our solar system was an anomaly.
Although those planets have masses comparable to Jupiter's - ranging from one-quarter to 17 times as large - their orbits differ from any in the solar system. All are closer to their stars, and many are very close, with a dozen zipping around their orbits in less than a week. Others have highly eccentric orbits, which could eject Earth-like planets.
Marcy's group watches for periodic changes in stellar velocity that reveal the pull of a planet orbiting the star. The planets have to be large to cause detectable motion.
After watching some stars for over up to 15 years, "we're finally entering the realm of detecting planets like those in our solar system," said Marcy's colleague Paul Butler of the Carnegie Institute of Washington.
But the survey still has a long way to go before we know if planetary systems like ours are common. Marcy and Butler now watch 1200 stars. Over the next year, they plan to expand their coverage to all 2000 stars within 150 light years. "I think we will be finding more of them," Butler said. However, he warns it will take a decade or so to "come up with hard numbers that say how common planetary systems like our solar system are."
Detecting Earth-like planets will take new technology and a new generation of instruments, said David Spergel of Princeton University. NASA has proposed building a space-based Terrestrial Planet Finder, but no money is in place and the tentative launch date is 2014.
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Discovery gives new hope for other Earths
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