Hot Jupiters, exoplanets giants snuggled up to their stars, are mysteriously puffed up. Their radii often exceed standard models by 50–100%. New models, based on transiting data (transit method), flip our understanding: heat doesn't come from the interior but from the upper atmosphere. Think of soup: if you heat only the surface, a thin layer boils while the rest stays cool. Similarly, heat gets trapped at the top, slowing interior cooling by 95–98%. This swelling can persist for eons. Even wilder: at 1500°C winds whip up, but at 1800°C they abruptly stop, like the planet overheats and turns off its own storm.
Some hot Jupiters complete an orbit around their star in less than an Earth day — on such a planet, a year is shorter than a day!