Friday, April 25, 2014

Kepler-186f: Facts, Speculation, and the Lemming

(From NASA Ames/SETI Institute/JPL-Caltech, used w/o permission.)

"NASA's Kepler Discovers First Earth-Size Planet In The 'Habitable Zone' of Another Star "
NASA Press Release (April 17, 2014)

"Using NASA's Kepler Space Telescope, astronomers have discovered the first Earth-size planet orbiting a star in the "habitable zone" -- the range of distance from a star where liquid water might pool on the surface of an orbiting planet. The discovery of Kepler-186f confirms that planets the size of Earth exist in the habitable zone of stars other than our sun.

"While planets have previously been found in the habitable zone, they are all at least 40 percent larger in size than Earth and understanding their makeup is challenging. Kepler-186f is more reminiscent of Earth.

" 'The discovery of Kepler-186f is a significant step toward finding worlds like our planet Earth,' said Paul Hertz, NASA's Astrophysics Division director at the agency's headquarters in Washington. 'Future NASA missions, like the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope, will discover the nearest rocky exoplanets and determine their composition and atmospheric conditions, continuing humankind's quest to find truly Earth-like worlds.'

"Although the size of Kepler-186f is known, its mass and composition are not. Previous research, however, suggests that a planet the size of Kepler-186f is likely to be rocky...."

That artists' concept is optimistic, assuming that Kepler-186f has an atmosphere like Earth's, and enough water for a substantial sea, at least. Whether or not the planet looks like that depends partly on what it's made of.

Scientists have worked out plausible scenarios where an Earth-size planet could be almost entirely water: which wouldn't be particularly good for fish, since life as we know it needs a broad variety of materials and water.

The odds are, in the Lemming's opinion, that Kepler-186f is a ball of rock and metal, like Earth. If it's Earth-like that way, it could have an atmosphere as spectacularly toxic as the one humans found around Venus: or no atmosphere at all.

Or astronomers may find a damp atmosphere of nitrogen and oxygen: and be puzzled by the planet's emission spectra, until someone realizes that they're looking at neon, helium, carbon dioxide, and mercury plasma from a continent-spanning analog of the Fremont Street Experience.

Kepler-186f: Cool, Literally

(From NASA Ames/SETI Institute/JPL-Caltech, used w/o permission.)

If Kepler-186f has something pretty close to Earth's chemical mix, including atmosphere, it'll probably be a tad cooler than the planet humans call home. Sunlight there at high noon is about as strong as Earth's an hour or so before sunset.

Kepler-186f is closer to its star than Earth: but its star is a whole lot dimmer than Sol.

What's the Big Deal?

(From NASA, used w/o permission.)

Until last week, scientists knew that planets orbit other stars, and that roughly 1/6 of the stars in this galaxy have planets roughly the same size as Earth. That works out to about 17,000,000,000 planets, give or take a few million, by the way. But they didn't know that any of these Earth-size planets orbited their stars far enough out for water to be a liquid.

Earth could have been a statistical fluke: a one-of-a-kind freak in an otherwise-lifeless universe.

Now scientists know of a planet that's only 10% wider than Earth, in an orbit that keeps it only slightly cooler than Earth. And they found it only 20 years after spotting the first planet circling another star.

Humans: They're not doing badly, at all.

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