An artist's onception of the Kepler spacecraft.

WASHINGTON, March 6 (Xinhua) -- NASA's Kepler space telescope, the world's first mission to hunt for extrasolar Earth-like planets, lifted off Friday night from Cape Canaveral Air Force Station in Florida.

The spacecraft is designed to find Earth-size planets orbiting stars in habitable zones -- regions where water could pool on the surface of the planets. Liquid water is believed to be essential for the formation of life.

It will watch a patch of space for 3.5 years or more for signs of Earth-sized planets moving around stars similar to the Sun. The patch that Kepler will watch contains about 100,000 stars like the Sun.

Using special detectors similar to those used in digital cameras, Kepler will look for slight dimming in the stars as planets pass between the star and Kepler.

The Kepler's place in space will allow it to watch the same stars constantly throughout its mission, something observatories like Hubble Space Telescope cannot do.