The Kepler Space Telescope changed the way we think about the Universe. NASA launched this observatory in 2009 with the goal of spotting Earth-like exoplanets in the habitable zones of Sun-like stars. By the time the mission ended in 2018, the telescope had studied some 150,000 Sun-like stars and found 2,300 exoplanets, about half of all that are known.
That’s an impressive achievement. But it hides some peculiar problems that the mission came up against. Kepler found that Earth-like planets around Sun-like stars turn out to be much harder to spot than anticipated. Consequently, astronomers have found it hard to make good estimates of the number that are likely to be nearby.
Now that has changed thanks to the work of Steve Bryson at NASA Ames Research Center and an international collaboration, who have crunched the numbers from Kepler in detail. Their work leads to the first estimate of the number of rocky planets in the habitable zones of Sun-like stars in our local neighborhood. The answer, they say, is that there are probably just 4 Earth-twins within 30 light-years of us.
