Why is the warm gas-giant exoplanet WASP-107 b so, so puffy? With a moderate temperature and an ultra-low density on par with a microwaved marshmallow, it seems to defy standard theories of planet formation and evolution.

Two independent teams of researchers think they’ve figured it out. Data from Webb, combined with prior observations from Hubble, show that the interior of WASP-107 b must be a lot toastier than previously estimated. The unexpectedly high temperature, which is thought to be caused by tidal forces that stretch the planet like silly putty, can explain how planets like WASP-107 b can be so floofy, possibly solving a long-standing mystery in exoplanet science.