Planet Styrofoam.

You’ve probably, by now, heard about the latest crop of distant planets discovered by the Kepler telescope. But have you read, in New Scientist or elsewhere, just how strangely light they are?:

The newly found planets are all less dense than expected based on models of how giant planets coalesce from gas.

One, called Kepler 7b, is about as dense as polystyrene. It is about 1.5 times as wide as Jupiter, but only about a tenth as dense, making it one of the most diffuse planets yet found.

Heat is thought to have caused this bloating, but the heating mechanism is not yet understood – it might be stellar radiation, gravitational tugs from the star, or something else.

“We think this has something to do with the fact that they are all very close to their host stars … but we haven’t found the smoking gun,” says team member Dimitar Sasselov of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

I’m waiting to hear that they’re all really made of souffle.