Seeing Double—Part 2

NASA’s Kepler mission has recently scored another success in its planet-finding work. (Kepler is a special telescope that orbits the sun as our Earth does, while keeping itself constantly pointed at a small, single patch of sky containing nearly 150,000 stars in a nearby part of our Milky Way galaxy.) This telescope has recently discovered several so-called “circumbinary” planets—worlds that orbit double stars. (Kepler has already found about a thousand planets orbiting single stars.) So now Kepler has also proven that planets orbiting double stars can and do exist. In fact, astronomers now estimate (from Kepler’s findings) that there may be “tens of millions” of circumbinary planets in our galaxy… in addition to the estimated billions of planets around single stars.

Yet it’s a whole other issue whether these circumbinary planets have any chance of harboring life. Our precious Earth orbits a single star in a nearly circular orbit—keeping the amount of solar heat falling upon us relatively constant. (We get seasonal temperature differences only because planet Earth’s axis tilts about 24° to its orbital plane, which points us towards the sun in summer and away from it in winter.) A planet that orbits two stars could experience wide and wild temperature swings, which would prevent life from either forming or surviving.

The Star Wars movie had a fascinating scene, in which the fictional planet Tatooine experienced a double sunset. Of course, the views of suns on real circumbinary planets could be bizarre and quite different from Tatooine. For example, it could be a case of one of two suns always shining down, bathing the planet in nearly constant daylight; or the lengths of days could vary wildly, as the double stars dance around each other; or the planet’s seasons could be random; etc.

Now we know that circumbinary planets do exist—thanks to Kepler. It’s one more fascinating piece of knowledge brought to us by our space programs. What’s next in this extra-terrestrial planet hunt? Astronomers are hoping to find an Earth-sized planet (around a solitary star) with an atmosphere like ours. If so, that would be a strong hint of the possibility of life “out there.” There’s no telling what the next discovery will be, but stay tuned—we are bound to learn more captivating details about our fantastic universe soon.