• Now You Know    April 17 
NASA discovers Earth-sized planet in habitable zone

It was only a matter of time.

[NASA Ames/SETI Institute/JPL-CalTech]

Today, researchers at NASA pinpointed the best candidate for life elsewhere in the universe: an Earth-sized planet — Kepler-186f, orbiting a dwarf star. The star, Kepler 18, is 6,500 lightyears from Earth in the constellation Cygnus.

The planet is closer to its star than Earth is to the Sun, but because Kepler 186 is a smaller star, the habitable zone — where water on its surface would be liquid — is closer in.

[NASA Ames/SETI Institute/JPL-CalTech]

Scientists don't yet know its composition, and so can't answer key questions like whether its surface is rocky, or whether it possesses liquid water— and, of course, the big question of whether or not it harbors any form of life.

This is likely to be the first of many. The planet was discovered using the Kepler space telescope, launched in 2009 with the specific aim of seeking out extrasolar planets. Kepler has found dozens of exoplanets, most of them gaseous giants like Jupiter, Saturn and Uranus. Large planets — particularly ones very close to their star — are easier to identify, because of the larger gravitational and dimming effects they have on their stars' light emissions. Smaller Earth-sized planets — and particularly ones relatively further away from their star, like Earth — have smaller effects, making them harder for scientists to detect.

So this is a pretty historic day in the history of astronomy, and the history of human civilization. Whether or not the planet contains life at present, at the very least that we have detected a good candidate outside our solar system to visit, and maybe one day colonize.

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