My two suns — could unusual planet point to alien life?
Some worlds have more than one sun in their sky. Now scientists say they’ve confirmed the existence of the largest known planet orbiting a pair of binary stars: a gas giant with the same mass and radius as Jupiter.
Exoplanets such as this one — situated in their stars’ habitable zone and massive enough to lasso in many rocky moons — could be an interesting place to look for signs of alien life.
The recently confirmed behemoth has been dubbed Kepler-1647 b, and it sits 3,700 light-years away in the constellation Cygnus. At an estimated 4.4 billion years old, it’s roughly the same age as Earth. But it’s nothing like our planet. It’s what is known as a circumbinary world — one that orbits two suns that dance together as a binary pair — and it’s the size of Jupiter, a planet with a diameter more than 11 times that of Earth. Its suns are pretty similar to our own but, well, there are two of them.
At about 2.7 astronomical units from its suns (Earth is one astronomical unit from ours), Kepler-1647 b is in the habitable zone of its stars. That means it’s in the magic sweet spot that experiences the right amount of sunlight and heat to allow liquid water to form.
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 harder to do with circumbinary planets, or CBPs.
“CBPs are harder to detect because their transits are not strictly periodic,” said Veselin Kostov, a NASA Goddard post-doctoral fellow and lead author of a soon-to-be-published study on the planet. “A planet around a single star is like a clock . . . In contrast, when a circumbinary planet transits, the consecutive events can be early or late by many days,” he said.
You might think that Kepler-1647 b, being significantly larger than previously discovered CBPs (all around the size of Saturn) would make a heftier dim and therefore be easier to spot. But it was actually 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 takes1,107 days for the planet to complete an orbit, the transit events that scientists can use to study it are few and far between.