There may be some 50 billion planets in the Milky Way galaxy, astronomers estimated using data gathered from the Kepler planet-hunting telescope.
Of those planets, some 500 million could be located in a key zone near their stars that could be conducive to life, dpa reported.
Scientists told the annual meeting of the American Association for the Advancement of Science the figure came from looking at a small portion of the sky that Kepler has so far examined and extrapolating how many planets could then be found in the Milky Way.
NASA said earlier this month that it had found 1,235 planet candidates, including 68 similar in size to Earth, orbiting more than 156,000 stars.
The Kepler mission is designed to discover other Earth-like planets in the Milky Way galaxy, but for those planets to be capable of harbouring life they must likely be located in what scientists dub the "Goldilocks" zone - neither too hot nor too cold.
The Kepler space telescope launched in 2009 is finely tuned enough to detect Earth-sized planets orbiting distant stars. The 590- million-dollar telescope programme is to spend at least the next three and a half years pointed at a large swath of the Milky Way galaxy, which contains about 4.5 million stars.
The most advanced cameras ever used in space are focussing on 100,000 to 150,000 stars deemed most likely to have orbiting planets, scientists said at a prelaunch press briefing. Data from the cameras is to be used to find planets by looking for distortions in the light emitted as an orbiting planet crosses in front of the star.