after 15 years of observation, a team of astronomers has found a planetary system that reminds us of our home solar system. Geoffrey Marcy, astronomy professor at Berkeley-based University of California, and astronomer Paul Butler of the Carnegie Institution of Washington dc, usa, have recently discovered a Jupiter-like planet orbiting a Sun-like star. "All other extrasolar planets discovered up to now orbit very close to the parent star, and most of them have elongated and eccentric orbits. This new planet orbits as far from its star as our own Jupiter orbits the Sun," said Marcy.
The star, 55 Cancri in the constellation Cancer, was already known to have one planet discovered by Butler and Marcy in 1996. That planet is a gas giant slightly smaller than the mass of Jupiter and revolves around the star in 14.6 days at a distance only one-tenth that from Earth to the Sun. Using as a yardstick the 93-million mile Earth-Sun distance called an astronomical unit (AU), the researchers say that the newly-found planet orbits at 5.5 AU, comparable to Jupiter's distance from the Sun of 5.2 au. Its slightly elongated orbit takes it around the star in about 13 years, comparable to Jupiter's orbital period of 11.86 years. It is 3.5-5 times the mass of Jupiter.
"We haven't yet found an exact solar system analog, which would have a circular orbit and a mass closer to that of Jupiter. But this shows we are getting close. We are at the point of finding planets at distances greater than four AU from the host star," said Butler. "I think we would be able to find them among the 1,200 stars we are now monitoring," he added. Discovery of a second planet orbiting 55 Cancri culminates 15 years of observations with the three metre-long telescope at Lick Observatory, owned and operated by the University of California, USA. Marcy and Butler used a technique that measures the slight Doppler shift in starlight caused by a wobble in the star's position due to the gravitational tug of an orbiting planet. By observing over a period of years, they were able to infer the planet's approximate mass and orbital size.