But the planet itself wouldn't actually be home to life as we know it: It's almost entirely made of gas. If it's anything like the gas giants in our solar system, however, it likely has dozens of moons - and just like the moons that orbit Saturn and Jupiter, those little rocky worlds could be great places to look for life like ours.
Scientists find exoplanets by measuring the way the light of their host stars dim when the planets "transit," or pass in front of the stars from our perspective. This is way harder to do with circumbinary planets, or CBP.
"CBPs are harder to detect because their transits are not strictly periodic," Veselin Kostov, a Nasa Goddard postdoctoral fellow and lead author of a soon-to-be-published study on the planet, told the Washington Post. "A planet around a single star is like a clock. For example, if you are outside the solar system and can see Earth in transit, you'll see the transit every year. Every 365 days you'll see a tiny decrease in the light from the Sun as Earth moves across its disk. In contrast, when a circumbinary planet transits, the consecutive events can be early or late by many days. Sometimes, the transits of a CBP can even cease altogether, only to reappear decades, even centuries later."
Sometimes, the transits of a CBP can even cease altogether, only to reappear decades, even centuries later
You might think that Kepler-1647 b, being significantly larger than previously discovered CBP (all around the size of Saturn or smaller) would make a heftier dim and therefore be easier to spot. But it was actually pretty hard to pin down: Kepler-1647 b has the longest orbit of any CBP ever detected. That distance from its host stars is good news for the potential for life on its moons, because it keeps them from getting too hot for liquid water. But since it takes 1107 days for the planet to complete an orbit, the transit events that scientists can use to study it are few and far between.
"The first transit was detected way back in 2011, but with one transit it's hard or impossible to tell what's going on," Kostov said. "So we had to wait for three years for the planet to transit again, during which time we kept a close eye in the system, analysing the available data and gathering new observations."
Scientists like to study systems with multiple host stars because they help us understand the myriad ways in which solar systems can evolve: It's been just a few years since we confirmed that planets could form in these strange, star-heavy systems, and now we know that in addition to (relatively) small planets kept in close orbit, the systems can develop large, slightly further-flung planets.
"Habitability aside, Kepler-1647 b is important because it is the tip of the iceberg of a theoretically predicted population of large, long-period circumbinary planets," study co-author William Welsh of San Diego State University said.
