Half Of All Solar Systems With Planets Are Binaries

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It now appears that Tatooine-like planets are far more common than previously thought. A new analysis of 1,000 known exoplanets shows that planets with two suns are an exceedingly frequent occurrence. But what does this say to the prevalence of life in our galaxy?

Binary star systems may account for as many as 50% of all stellar systems. But what's less known is the rate at which such systems can produce exoplanets. A team of astronomers led by Elliott Horch of Southern Connecticut State University has now shown that stars with exoplanets are just as likely to have a binary companion. Specifically, between 40% to 50% of host stars are actually binary stars.


"It's interesting and exciting that exoplanet systems with stellar companions turn out to be much more common than was believed even just a few years ago," noted Horch in a National Optical Astronomy Observatory statement.

Steve B. Howell of NASA Ames Research Center, and a co-author of the study, added that, "An interesting consequence of this finding is that in the half of the exoplanet host stars that are binary we can not, in general, say which star in the system the planet actually orbits."


Indeed, to date astronomers have only discovered one binary star system featuring a rocky planet in a stable orbit. Other binary systems feature gas giants, including a system with multiple planets.


In addition,

Kepler has discovered a number of circumbinary planets, that is, a planet that orbits both stars in very close binary systems. There also exist exoplanets that are known to orbit one of the stars in very wide binary systems. If the two stars are very close to each other and the planet far away, a circumbinary planet will be reminiscent of Tatooine in Star Wars.


If instead the exoplanet orbits one of the stars in a very wide pair, the companion star might appear simply as a bright star among others in the night sky. "Somewhere there will be a transition between these two scenarios," Howell said," but we are far from knowing where."


Armed with this information, and given the preponderance of such systems in our galaxy, astrobiologists will now have to figure just how potentially habitable these exoplanets are compared to those in single-star systems (they'll also have to develop a taxonomy of binary exoplanets to chart the frequency of circumbinary planets compared to those in wide orbits). If habitable potential is dramatically diminished in binary systems — which it very well could be — that could pose a significant blow to our conception of how common life is the universe.

Well, at least by half.

This work has been accepted for publication in the Astrophysical Journal.

Top image: Artist's conception via NASA/JPL-Caltech/Univ. of Ariz.

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