Astronomers discover first quintuple-planet system

Star 55 Cancri became the only star aside from the sun to have five planets, when American astronomers announced Tuesday the discovery of the fifth planet.

The solar system of 55 Cancri resembles Earth's, with four inner planets and one giant outer planet in stable, nearly circular orbits, but without planets Earth and Mars. The system is located 41 light-years away in the direction of the constellation Cancer.

The team of astronomers from the California and Carnegie planet search team have been observing the star for 19 years, and found the fifth planet using the Doppler technique, in which a planet's gravitational tug is detected by the wobble it produces in the parent star.

To make the discovery, the researchers observed nearly 2,000 nearby stars with the Shane telescope at Lick Observatory near San Jose, Calif., and the W.M. Keck Observatory in Mauna Kea, Hawaii.

The new planet is a ball of gas about 45 times the size of Earth, but similar in age and distance away from its sun, the star. The astronomers said it may resemble Saturn.

While the new planet is full of gas, lead author Debra Fischer from San Francisco State University said it is within the area where liquid water could exist on the surface of a moon or other planets within its zone.

"Right now, we are looking at a gap between the 260-day orbit of the new planet and the 14-year orbit of another gas giant, and if you had to bet, you'd bet that there is more orbiting stuff there," she said in a release, adding that whatever may be in the gap would need to be Neptune-sized or smaller, because anything larger would destabilize the outer planets.

The first planet around 55 Cancri was discovered in 1996, with the second and third following in 2002. The fourth was discovered in 2004, very close to the star. Astronomers have found nearly 250 exoplanets, but so far only one other star, mu Ara in the southern sky, is known to have four planets.

The team's finding will be published in the upcoming edition of the Astrophysical Journal.