NASA's Kepler spacecraft has discovered two potentially liveable planets orbiting around a sun-like star in their mission to scout for "habitual" planets similar to ours.

In total, NASA-funded Kepler mission discovered five planets orbiting around a star called Kepler-62. Of them, two of the planets, named 62e and 62f, have been deemed the most conducive to human survival.

Earth-like Planets
Comparison of sizes of Kepler-69c, 62e, 62f and the Earth.

The scientists involved in the mission published their report in the journal Science that 62e and 62f were "habitual" for human habitation. By habitual, they meant that the temperature on the two planets were neither too hot nor too cold, and could possibly contain water. The planets are placed in the "Goldilocks zone", where the temperatures are perceived to be moderate, and not swaying to the extremes.

William Borucki, principal researcher of NASA's Kepler mission, explained: "They are close enough to their star (Kepler-62) to be warm, but not so near as to boil the oceans. They are far enough to maintain the likelihood of water without freezing the seas solid."

"These two (planets) are our best candidates that might be habitable," he added.

The two planets, which are situated some 1,200 light years away from our planet in the constellation Lyra, are orbiting a seven-billion old star. The NASA research concludes that the two "habitual" planets comprise of rock, ice or a mix of rock and ice, which would raise hopes of finding water in another planet except ours.

Planet 62e is about 40 percent larger than earth, while the second, 62f, is around 60 percent larger than our planet. Another familiarity with our planet would be that 62f takes similar time orbiting its star. 62f takes 267 days, which is close to earth's trajectory around the sun.

Also, Borucki said the second planet "may have polar caps, significant land masses and liquid water".

Co-researcher of the NASA mission David Charbonneau was excited about the latest discovery, and felt that planet 62-f had all the ingredients to support life.

Kepler is a space observatory launched by NASA with a mission to scout for earth-like planets orbiting stars. As of January 2013, the mission has chosen a total of 2,740 candidates, planets which have been believed to be life-friendly.