Nov 7, 2007
The discovery brings to five the number of planets orbiting the star, 55 Cancri, the most found to date in a single solar system outside our own.
Astronomers have found more than 250 planets outside our own solar system - the team behind the latest discovery have found more than anyone else.
The new planet is a gas planet about 45 times the mass of the Earth.
Their latest find is a fifth planet to add to the four they had already discovered around 55 Cancri, a double or binary star in the constellation of Cancer.
If the new planet, which has mild surface temperatures, has a rocky moon or moons around it, say the astronomers, then theoretically they could support liquid water.
But it is the bigger picture that is really intriguing these planet hunters.
They say this quintuple planet system has many similarities to our own.
The planets orbit a star which is similar in age and mass to our own Sun and the system also boasts its own gas giant - a planet four times the mass of our own Jupiter in a similar orbit to Jupiter.
What they have not yet found is a rocky planet like the Earth or Venus, but according to Professor Geoff Marcy, of the University of California, Berkeley, who led the work, that may only be a question of time and technology.
"There is an intriguing, mysterious gap between the fourth planet out around 55 Cancri and the Jupiter-like planet that's far away," he says.
"In that gap, we don't know what there is. Our current technology would be able to detect big planets like Neptune, Saturn and Jupiter. We don't see any of them.
"So if there are any planets there, they must be smaller, the size of the Earth.
"In fact, it's a little hard to imagine that there's just nothing there in this big gap. So the suggestion is there might be small rocky planets, like Venus, Mars or Earth."
Of course, none of these planets can actually be seen - the astronomers use tiny wobbles in the movement of the star to detect the presence of planets tugging on the star as they encircle it.
But you can see the star itself - 55 Cancri - easily, with only a pair of binoculars, at the right time of year and with a clear night sky.