Most Earth-like planets discovered: NASA

WASHINGTON - Two new planetary systems that include three most Earth-like planets in the so-called "habitable zone," the range of distance from a star where the surface temperature of an orbiting planet might be suitable for liquid water, have been identified, scientists from US space agency NASA reported in the journal Science on Thursday.

The Kepler-62 system has five planets: 62b, 62c, 62d, 62e and 62f. The Kepler-69 system has two planets: 69b and 69c. Kepler-62e, 62f and 69c are the most Earth-like planets.

Orbiting its star every 122 days, Kepler-62e was the first of these habitable zone planets discovered by NASA's Kepler telescope, which was launched in 2009 to discover Earth-like planets orbiting other stars. Kepler-62e is roughly 60 percent larger than Earth.

Kepler-62f, with an orbital period of 267 days, was later found. It is only 40 percent larger than Earth, making it the exoplanet closest to the size of our planet known in the habitable zone of another star. Researchers said that Kepler-62f is likely to have a rocky composition.

The third planet, Kepler-69c, is 70 percent larger than the size of Earth, and orbits in the habitable zone of a star similar to the Sun. Astronomers are uncertain about the composition of Kepler-69c, but its orbit of 242 days around a Sun-like star resembles that of our neighboring planet Venus.

Scientists said they do not know whether life could exist on the newfound planets, but their discovery signals we are another step closer to finding a world similar to Earth around a star like our Sun.

"The discovery of these rocky planets in the habitable zone brings us a bit closer to finding a place like home," said John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington in a statement.

"It is only a matter of time before we know if the galaxy is home to a multitude of planets like Earth, or if we are a rarity," Grunsfeld added.