How's this for an astronomical estimate? There are at least 50 billion exoplanets in our galaxy. What's more, astronomers estimate that 500 million of these alien worlds are probably sitting inside the habitable zones of their parent stars.
So how many of these exoplanets have life? Unfortunately, there's no estimate for that question.
This announcement was made on Saturday by Kepler science chief William Borucki at the American Association for the Advancement of Science in Washington D.C. However, Kepler didn't actually count 50 billion exoplanets, this number comes from extrapolations of the data taken so far by the exoplanet-hunting space telescope.
For example, as Kepler has spotted 1,235 exoplanet candidates so far -- 53 of which orbit stars in their habitable zones -- knowing approximately how many stars there are in our galaxy (there are thought to be around 300 billion stars in the Milky Way), an estimate can be made of how many worlds are orbiting these stars.