There Could Be Billions of Earth-Like Planets in the Milky Way Alone

One out of every five Sun-like stars in our galaxy has an Earth-like planet in orbit, according to an exciting new analysis of data collected from NASA's Kepler telescope. 

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One out of every five Sun-like stars in our galaxy has an Earth-like planet in orbit, according to an exciting new analysis of data collected from NASA's Kepler telescope. The Kepler, which recently ended its mission to find Earth-like planets, provided years' worth of data for scientists to dive into in the search for other worlds with conditions amenable to hosting life. The latest study out of that trove is evidence that we're far from hearing the end of Kepler's work.

The analysis is actually an educated estimation based on data collected from one small sample of our galaxy, using Kepler's technique for detecting planets around other stars. Looking at a planet at the proper angle, the telescope could detect slight dips in light from far away stars. Those dips, reliably, represent a planet orbiting between the sun and the device, blocking some of the light. And the amount of light it blocks indicates the size of the planet. That's how Kepler identified over 3,500 potentially Earth-like planets over its tenure. For the most recent study, a team of researchers concentrated on data from 42,000 Sun-like stars. 603 of those stars contained candidate planets in orbit, only 10 of which turned out to be Earth-like, defined here as having a similar size and distance of orbit to Earth's.

Although those 10 planets are not necessarily of similar composition to Earth, the same team's discovery of an impossibly hot (yet very similar) world 400 light-years away has given some confidence that the identified planets could indeed have a rocky surface. And scientists potentially have many more than 10 planets to work with: As Slate points out, there are about 20 billion Sun-like stars in the Milky Way. That adds up to potentially tens of billions of Earth-like planets in the sky around us. And if the sample is representative of the rest of the galaxy, the closest Earth-like world could be fewer than 12 light-years away from us. That's pretty darn close, in interstellar terms. Hawaii-based researcher Andrew Howard explained why these estimates are so valuable:

"For NASA, this number – that every fifth star has a planet somewhat like Earth – is really important, because successor missions to Kepler will try to take an actual picture of a planet, and the size of the telescope they have to build depends on how close the nearest Earth-size planets are." 

Kepler itself, as we mentioned before, is out of commission. The telescope went into semi-retirement after two of its four navigational wheels broke, rendering it incapable of the precise moves required to monitor for planets. Since the craft orbits the Sun and not the Earth, sending out a repair team was out of the question. Earlier this year, NASA collected ideas for continued use of Kepler on projects requiring less precision. In the meantime, scientists still have at least a year of Kepler data to sort through.

This article is from the archive of our partner The Wire.