Meet Kepler-413b: A wobbly planet with strange seasons
This planet, called Kepler-413b, is about 2,300 light-years away in the constellation Cygnus, and it orbits a binary pair of stars that are circling each other. This gas giant weighing roughly 65 Earth masses orbits every 66 days, too close to the stars to be habitable.
But here's the unusual bit about this planet, described in a forthcoming issue of the Astrophysical Journal: It's so wobbly that its spin axis could vary by as much as 30 degrees over 11 years - a pretty extreme swing, given that the Earth, tilted at 23.5 degrees, completes one round of its own "wobble" every 26,000 years.
The team discovered this strange system while looking for planets crossing in front of binary stars, said lead author Veselin Kostov, an astrophysicist with Johns Hopkins University and the Space Telescope Science Institute in Baltimore.
But Kepler-413b was anything but regular. The dips in brightness occurred in weird fits and starts: three times in the first 180 days, then not at all for the next 800 days, then five more times before it stopped again (and then Kepler ceased functioning).
The scientists realized that the planet's orbit was off by 2.5 degrees - it didn't travel in the same plane as its host stars, a red dwarf and a slightly larger orange dwarf. The scientists think that, as this uneven pair of stars dance around each other at the center, their different gravitational pulls constantly warp the planet's orbit. It also causes the planet to wobble.
The seasons on this gassy planet, such as they are, would be in constant flux, Kostov said. And this has implications for a detailed definition of habitability. Just because a planet lies in the habitable zone doesn't mean it's a friendly place to live.