Marshmallow world: WASP-107b is a superpuff planet with a weirdly tiny core

With over 4,300 confirmed exoplanets found — alien worlds orbiting alien stars — there are bound to be a few oddballs.

And then there’s WASP-107b. It’s a “puffball planet,” one with a large size but low mass, making it extremely low density. And new research shows it’s even weirder than that: The core of the planet is likely far smaller than astronomers previously thought a gas giant core could be, making it hard to understand how it even formed in the first place.

WASP-107b was discovered in ...