The Kepler space telescope has discovered 715 planets outside our solar system, including four that are potentially habitable, NASA said.

Kepler, launched in March 2009, is NASA's first mission to detect Earth-size planets with conditions to support life.

The telescope, according to exoplanet exploration program scientist Douglas Hudgins, "has really been a game-changer for our understanding of the incredible diversity of planets and planetary systems in our galaxy."

Data from Kepler shows that planetary systems "are quite common," Jason Rowe, research scientist at the SETI Institute in Mountain View, California, said during a teleconference.

All but 5 percent of the planets discovered by Kepler are smaller than Neptune, Rowe said.

Neptune is four times the size of the Earth.

"From this study we learn planets in these multi-systems are small and their orbits are flat and circular," Rowe said.

"This latest discovery brings the confirmed count of planets outside our solar system to nearly 1,700," NASA said in a statement.

Kepler has detected nine exoplanets in the "habitable zone," designating conditions that permit the existence of water in liquid form. EFE