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A NASA scientist leading the search for life on other planets claims a major breakthrough could be made within the next 20 years.
The rate at which potentially habitable planets are being identified is soaring, helping scientists to narrow down their search for extraterrestrial life.
When the first exoplanet was discovered in 1992, many regarded it as a once-in-a-lifetime event, but 25 years later, over 3,500 exoplanets from thousands of star systems have been located.
Several of these are orbiting within their star's "habitable zone" - where surface temperatures range from nought to 100 degrees centigrade, allowing liquid water to pool on the surface.