Fifth planet is 'exciting next step'

The discovery of a fifth planet circling a star beyond our solar system marks “an exciting next step in the search for worlds like our own”, astronomers said today.

The new planet has nearly the same mass and age as our sun, is “easily visible” with binoculars, and is located in a so-called “habitable zone,” a band around the star where the temperature would permit liquid water to pool on solid surfaces, NASA said.

The space agency said the star, 55 Cancri, now holds the record for the number of confirmed extra-solar planets orbiting around it in a system.

Michael Briley, an astronomer at the National Science Foundation in Virginia, said: “This work marks an exciting next step in the search for worlds like our own.

“To go from the first detections of planets around sun-like stars to finding a full-fledged solar system with a planet in a habitable zone in just 12 years is an amazing accomplishment and a testament to the years of hard work put in by these investigators.”

Weighing 45 times the mass of the Earth, the new planet is 41 light-years away, may be similar to Saturn in its composition and appearance, and completes one orbit every 260 days, a Nasa spokesman said.

Alan Stern, associate administrator for the Science Mission directorate at Nasa headquarters in Washington, said: “It is amazing to see our ability to detect extra-solar planets growing.

“We are finding solar systems with a richness of planets and a variety of planetary types comparable to our own.”

Researchers discovered the planet using the Doppler technique, in which a planet’s gravitational tug is detected by the wobble it produces in the parent star.

The distance from its star is about 72.5 million miles, slightly closer than Earth to our sun, but it orbits a star that is slightly fainter.

Debra Fischer, lead author of a paper that will appear in a future issue of the Astrophysical Journal, said: “The gas-giant planets in our solar system all have large moons.

“If there is a moon orbiting this new, massive planet, it might have pools of liquid water on a rocky surface.”

Prof Fischer, an astronomer at San Francisco State University, added: “This is the first quintuple-planet system.

“This system has a dominant gas giant planet in an orbit similar to our Jupiter. Like the planets orbiting our sun, most of these planets reside in nearly circular orbits.”

Astronomer Geoff Marcy, of the University of California, Berkeley, said the discovery of five extra-solar planets orbiting a star was “only one small step”.

“Earth-like planets are the next destination,” he said.