NASA's Kepler Satellite telescope has spotted and identified 1,284 new planets outside our solar system, including more than a hundred Earth-sized planets orbiting alien stars.

The US space agency says this is the biggest single announcement of the discovery of new exoplanets.  The Kepler space craft is able to more clearly see heavenly bodies because it is in a heliocentric orbit, following the Earth around the Sun without being affected by light sources or gravitational fields.

Although only nine of the newly discovered planets are within their star system's "habitable zone" - where conditions are favorable for the existence of liquid water which would sustain life as we know it - Kepler scientists say their could be more than 10 billion potentially habitable planets in the Milky Way.

"About 24 percent of the stars harbor potentially habitable planets that are smaller than about 1.6 times the size of the Earth.  That's a number that we like because it's below that size that we estimate planets are likely to be rocky," said Dr. Natalie Batalha, a Kepler mission scientist at NASA's Ames Research Center in California.  "If you ask yourself where is the next habitable planet likely to be, it's within about 11 light-years, which is very close," she added.