It lies right in the centre of the star's habitable zone, where potentially perfect conditions exist for life.
Two other small planets orbiting stars smaller and cooler than the Sun have recently been found at the very edges of their habitable zones. Their orbits more closely resemble those of Mars and Venus.
A report on the discovery will be published by the Astrophysical Journal.
The planet was spotted after making a "transit" across the front of its parent star, causing the star's brightness to dip.