Astronomers announced on Monday that the Kepler space telescope sent into deep space by NASA has discovered 1,284 exoplanets. Among them, nine rocky planets might be able to support life as we know it. This is the biggest haul ever revealed so far by the space agency.

The overall tally is now around 3,200 alien planets in which 2,235 has been discovered by Kepler, said NASA officials.

"We now know that exoplanets are common, most stars in our galaxy have planetary systems and a reasonable fraction of stars in our galaxy have potentially habitable planets," said Paul Hertz in a news conference on Tuesday. He is the Astrophysics Division director at NASA Headquarters in Washington, D.C.

"Knowing this is the first step toward addressing the question, 'Are we alone in the universe?'" he added.

His assessment is logical considering that the data collected by Kepler and other instruments indicate that around 25 percent of all the "normal" stars in the Milky Way galaxy hold Earth-size planets in their habitable zones.

Kepler uses a phenomenon called "transit" to find new alien worlds. This is the process wherein one planet passes in front of its star, and seen from the visual perspective or viewpoint of another planet.

The space probe tracks the subtle dimming of distant stars to distinguish probable planets that orbit them. This is the best method NASA is using to discover exoplanets, even if it can only search for alien worlds by using the "transit" method from our planet's perspective.

The Kepler mission was launched in March 2009 and is kept running by a $600 million budget. Its main objective is to determine how common Earth-like planets are in the Milky Way.

There are at least 70 billion main-sequence starts in our galaxy according to Natalie Batalha, mission scientist at the Ames Research Center of NASA. So, Kepler has still a long way to go in fulfilling its mission.