Randy McDonald (rfmcdpei) wrote,
Randy McDonald

[BRIEF NOTE] On the coolness of exoplanet Kepler-16b

Astronomers continuing to go through the data on exoplanets collected by the Kepler space observatory have found yet another surprising exoplanet. This one is being compared to Star Wars's planet of Tatooine, for Kepler-16b is the first planet found (like Tatooine itself) to orbit two stars at once.

Kepler-16 A, B, and b

A fairly tight binary pair, the Extrasolar Planets Encyclopedia identifies star A as a relatively bright orange dwarf and star B as a dim red dwarf, the two separated by half the average distance of Mercury from our sun and sharing a 41-day orbit around a point of common gravity. Kepler-16b orbits this point. From the NASA perspective, this makes Kepler-16b almost the perfect exoplanet.

Astronomers further observed that the brightness of the system dipped even when the stars were not eclipsing one another, hinting at a third body. The additional dimming in brightness events, called the tertiary and quaternary eclipses, reappeared at irregular intervals of time, indicating the stars were in different positions in their orbit each time the third body passed. This showed the third body was circling, not just one, but both stars, in a wide circumbinary orbit.

The gravitational tug on the stars, measured by changes in their eclipse times, was a good indicator of the mass of the third body. Only a very slight gravitational pull was detected, one that only could be caused by a small mass. The findings are described in a new study published Friday, Sept. 16, in the journal Science.

"Most of what we know about the sizes of stars comes from such eclipsing binary systems, and most of what we know about the size of planets comes from transits," said Doyle, who also is the lead author and a Kepler participating scientist. "Kepler-16 combines the best of both worlds, with stellar eclipses and planetary transits in one system."

This discovery confirms that Kepler-16b is an inhospitable, cold world about the size of Saturn and thought to be made up of about half rock and half gas. The parent stars are smaller than our sun. One is 69 percent the mass of the sun and the other only 20 percent. Kepler-16b orbits around both stars every 229 days, similar to Venus’ 225-day orbit, but lies outside the system’s habitable zone, where liquid water could exist on the surface, because the stars are cooler than our sun.

The NASA press release later quotes reaction from Industrial Light & Magic, the business responsible for Star Wars' special effects.

The nearest close binary of Sun-like stars that--unlike Kepler-16--might support a fully Earth-like world is Delta Trianguli, some 35.4 light years away. Turning back to the Kepler-16 system and its own potential for life, a Saturn-sized world might plausibly support a Titan-sized moon that could support a prebiotic chemistry, but that's absurdly speculative. (Wait a decade?)
Tags: extraterrestrial life, saturn, space science, titan
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