NEW DELHI (TIP): It is no longer a question of will we find a true Earth analogue, but a question of when, says Steve Howell, project scientist at the NASA mission that is searching for new planets orbiting other stars. On Monday, NASA announced that its Kepler space telescope had discovered 461 new planet candidates. With this addition, the number of potential planets discovered so far has gone up to 2,740 orbiting 2,036 stars. That’s a 20 percent increase since data was released in February last year. Four of the potential new planets revealed are less than twice the size of Earth and orbit in their sun’s “habitable zone,” the region in the planetary system where liquid water might exist on the surface of a planet, NASA said in a statement. Just like our Solar System, 43 percent of Kepler’s planet candidates are observed to have neighbor planets.

The new data increase the number of stars discovered to have more than one planet candidate from 365 to 467. “The large number of multicandidate systems being found by Kepler implies that a substantial fraction of exoplanets reside in flat multi-planet systems,” said Jack Lissauer, planetary scientist at NASA’s Ames Research Center in Moffett Field, Calif. “This is consistent with what we know about our own planetary neighborhood.” The Kepler space telescope identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars in search of planets that pass in front of, or “transit,” their host star. At least three transits are required to verify a signal as a potential planet.

Scientists analyzed more than 13,000 transit-like signals to eliminate known spacecraft instrumentation and astrophysical false positives, phenomena that masquerade as planetary candidates, to identify the potential new planets. Candidates require additional follow-up observations and analyses to be confirmed as planets. At the beginning of 2012, 33 candidates in the Kepler data had been confirmed as planets. Today, there are 105. Kepler space telescope, named after the 17th century German astronomer Johannes Kepler was launched in March 2009. It is fixedly looking at a view that covers about 145,000 stars in the neighborhood of the Solar System, within the Milky Way.