Astronomers Find First Earth-Sized Exoplanet in Habitable Zone

Astronomers Find First Earth-Sized Exoplanet in Habitable Zone
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Our sun is not the only star in the Milky Way Galaxy; that goes without saying. In fact, it has at least 400 billion brothers and sisters! So if our treasured sun has such an extended stellar family, surely Earth is not alone...

Thus far, astronomers have spotted around 1,800 exoplanets. Some are big. Some are small. Some are even similar in size to Earth. More are gassy. A few are rocky. And a select bunch, around 20 or so, even reside with the prized "Goldilocks zone," the region around a star within which planetary objects with sufficient atmospheric pressure can support liquid water on their surfaces.

But so far, astronomers haven't discovered a planet combining the best of both worlds: Earth-sized and inside its star's habitable zone. Such a planet would surely be a prime candidate for supporting life as we know it!

Well, that planet-finding drought is over. With a paper in the prestigious journal Science, a team primarily based out of NASA's Ames Research Center and the SETI Institute has announced the discovery of such a planet.

Ladies and gentlemen, meet Kepler-186f. With a radius roughly 1.11 times larger than Earth's, it could be a slightly bigger sibling to our home planet. The outermost planet in a system with four others, Kepler-186f orbits its star every 130 days at a distance of roughly 30 million miles, much closer than Earth's 93 million miles. One might be worried that Kepler-186f would be baked to a crisp, but that's not a concern -- the planet's sun is a little less than half the size of ours. So rather than smoldering, Kepler-186f receives just 32% of the intensity of solar radiation that Earth receives.

"Despite receiving less energy than Earth, Kepler-186f is within the habitable zone throughout its orbit," lead author Elisa Quintana, an astrobiologist at NASA's Ames Research Center, reassuringly writes.

However, if there's liquid water on the surface, it may be in danger of freezing.

"It is... slightly larger than the Earth, and so the hope would be that this would result in a thicker atmosphere that would provide extra insulation," San Francisco State University astronomer Stephen Kane, also a member of the team, said in a press release.

The chances of life on Kepler-186f are hampered by a glaring fact: M-class Stars like Kepler-186 have a bad habit of emitting flares, flares that are proportionally more powerful than those emitted by our sun. And as Kepler-186f is much, much closer than Earth is to the Sun, the planet might be periodically hit by a flare, which could wreak all sorts of havoc.

Quintana and her compatriots are very certain of Kepler-186f's size, but they are less certain about some of the planet's other features, like its atmosphere, mass, and composition. Sometimes, astronomers can analyze the spectrum of light given off when a star's light traverses a planet's atmosphere, allowing them to determine the elements present. But sadly, Kepler 186f's sun is far too dim for spectroscopy to be feasible. However, given its radius, it is highly unlikely that the planet has a hydrogen-rich atmosphere like Jupiter, Saturn, or other gas giants.

Kepler-186f could be composed of pure ice, pure rock, or even pure iron, yielding a range of masses from 32% that of Earth's to 3.77 times as much. If it features an Earth-like composition, it would be 44% more massive.

The team also isn't sure of Kepler-186f's rotation. For instance, if it's tidally locked, one side would always face its sun.

The discovery was made using the Kepler Space Telescope. The stargazing machine primarily locates planets by observing faraway stars. As planets pass in front of these stars, some of the light they emit is blocked. By studying this occluded light, astronomers can glean all sorts of information, like a planet's size, density, and sometimes even the content of its atmosphere.

If you're hankering to travel to Kepler 186f, you're sadly out of luck. The planet is roughly 500 light years away. But look on the bright side: we've just found a planet that's a lot like ours! Earth is not alone! Who knows, maybe we're not either!

Source: Elisa V. Quintana et. al. "An Earth-Sized Planet in the Habitable Zone of a Cool Star." SCIENCE VOL 344 18 APRIL 2014

(Top Image: Danielle Futselaar)

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