For the first time ever, astronomers have discovered a system of seven Earth-sized planets orbiting around a single star. The finding was announced Wednesday by officials from NASA the U.S. space agency and other research team members. The discovery was also published in the journal Nature. Scientists said three of the newly discovered planets are in the so-called habitable zone. This is the area around the parent star where a rocky planet is most likely to have liquid water, and possibly life.