Back in September, NASA's planet-hunting satellite Kepler made one of its most dramatic discoveries when it spotted a planet orbiting two stars. But was this a one-of-a-kind cosmic freak, or are there lots of these strange planets? Now we know.
Kepler-34b and Kepler-35b are two new examples of so-called circumbinary planets, joining the previously discovered Kepler-16b. In both of these new star systems, the double suns orbit each other, and the planets orbit the combined gravitational field of the two stars. You can see an absolutely eye-popping simulation of a circumbinary planet and its orbit in the video up top.
Both of these newly discovered planets are gas giants, roughly the same volume as Jupiter but significantly less massive. Kepler-34b, for instance, is 76% the size of Jupiter, but has just 22% of our gas giant's mass. Similarly, Kepler-35b is 74% Jupiter's volume, but just 12% of its mass. This lightness is likely due to their mostly hydrogen atmospheres. The two occupy orbits roughly equivalent to a space somewhere between Venus and Earth, with Kepler-34b orbiting every 288 days and Kepler-35b every 131.
While neither of these planets — nor Kepler-16b, for that matter — could support life even if they were in a normal star system, their discovery means that there are likely millions and millions of circumbinary planets throughout the Milky Way. Before Kepler found these two, astronomers couldn't be sure whether such planets really were a regular fixture of binary star systems, or if Kepler-16b was simply a unique cosmic oddity.
Now we know such worlds are common, the question then becomes what a rocky planet might look like in such a system, particularly one that might be capable of supporting life. In a press release, University of Florida astronomer Eric B. Ford describes the kind of climatic conditions you would experience on a circumbinary world:
"Circumbinary planets can have much more complex climates, since the distance between the planet and each star change significantly during each orbital period, the length of an alien planet's year. For Kepler-35b, the amount of incoming star light changes by over 50 percent within a single Earth year. For Kepler-34b, each Earth-year brings 'summers' with 2.3 times as much star light as winters. Over the course of a year, the change in the amount of sunlight heating the Earth varies by only 6 percent."
Of the 160,000 stars that Kepler has observed, 2,165 of them are binary star systems. Right now, we know three of them support life - but it's possible that number is about to skyrocket as our ability to detect these circumbinary planets increases.