The planets suite

11 November 2007
Posted by Chris Smith.

Space scientists have discovered a fifth planet in a nearby star system, making it the largest planetary group yet observed around a distant star.

Astronomers have been watching the the distant star, which is called 55 Cancri and is 41 light years (or 5.8 trillion miles) away in the direction of the constellation of Cancer, for the past 18 years.  The system is too far away to see individual planets, but they can be detected by picking up tell-tale wobbles in the light coming from the star caused by the gravitational pull of orbiting bodies.  Using this technique, in the mid 1990s, researchers found a planet the size of Jupiter orbiting the star every 14 days.  Then, between 2002 and 2004, a further 3 planets were discovered.

One, which is similar in size to Neptune and about 14 times bigger than the Earth, sits sizzlingly close to the star and completes an orbit in just 2.8 days.  The other two planets include a massive body, which is four times larger than our own Jupiter and orbits once every 14 years, and a Saturn-sized planet with a 44 day orbit. 

The newly discovered planet is also huge and at least 45 times the size of Earth, but it's got scientists intrigued because it has a 260 day orbit, similar to the trajectory of Venus in our own solar system.  This means that it's likely to be a warm world, like the Earth. And although it's much larger than the Earth, it may well have a number of rocky moons, and if these contain water then the warm temperatures may well make them wet and ideal places where life could flourish.  The discovery, which has been made by Debra Fischer from San francisco State University and Geoff Marcy from the University of California at Berkley, marks the first time astronomers have found a planetary system with more than four planets.

"We now know that our Sun and its family of planets is not unusual," says Marcy.

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