The new planet is more like Saturn than Earth, but like Saturn, it could have rocky moons. In theory, a moon the size of Mars orbiting the planet could have enough gravity to keep water molecules from escaping and maintain an atmosphere that would allow life to thrive.

But this is not a highly likely scenario.

"All of the giant planets in our solar system do have large moons," Marcy said. "But the notion of a habitable moon is a reach."

More likely is the possibility of smaller planets in the 55 Cancri system.

Our solar system is pretty near its planetary capacity, with each planet's gravitational zone nearly bumping up against that of its neighbors. There aren't a lot of big gaps where another stable orbit could be added. But there is a sizable gap around 55 Cancri that could easily contain several small planets within the habitable zone. But astronomers will have to wait for technology to catch up before they'll know.

"For all we know, there may be Earth-sized planets around every star," said planetary scientist and discovery team member Jonathan Lunine of the University of Arizona in Tucson.

"We just can't see them yet."

The new planet makes that idea even more tantalizing.

"We can now say there are stars like the sun with many worlds around them," Lunine said.