Researchers say the newly discovered planet is too close to its sun to support known forms of life - it has a surface temperature estimated at 1200C. But previous studies suggest that when one planet is discovered orbiting a sun there are usually others in the same system.
The Earth-sized planet, the discovery of which was announced by Stephane Udry and Xavier Dumusque, of the Geneva Observatory, orbits one of the suns in the three-star Centauri system, roughly 40 trillion kilometres away.
"It's a landmark discovery because it has a very low mass and it's our closest neighbour," said Udry. "Its orbit is very close to its star and it must be much too hot for life as we know it but it may well be just one planet in a system of several."
