Astronomers have identified two giant exoplanets whose material is so diffuse that, by density, a chunk of them would float right through a bowl of candy floss.
An international team has discovered two of the fluffiest giant planets ever found. Roughly the size of Jupiter but only a tiny fraction of its mass, the two worlds orbit a star more than a thousand light-years away and carry densities lower than cotton candy. They are the largest "super-puff" planets known — a class of objects that, at first glance, seem to violate everything we expect of a gas giant.
A gas giant is normally a dense, heavy world held together by its own crushing gravity. Jupiter's average density is about 1.33 grams per cubic centimetre. Cotton candy, by contrast, is almost entirely empty space — its average density is closer to 0.1 gram per cubic centimetre. These new planets sit somewhere in between Jupiter's size and cotton candy's fluff, meaning their atmospheres must be extraordinarily puffed out and extremely tenuous.
The key puzzle is formation. A planet that light should not be able to hold on to a giant gaseous envelope at all — the host star's heat and radiation pressure should have stripped it away. The two new super-puffs suggest they may have assembled far from their star, where ices and gases were plentiful and cold, then migrated closer in. Their delicate haze layers and puffed atmospheres are what keep the density so low even after they warmed up.
Each confirmed super-puff is a data point for planetary scientists trying to understand how worlds form, migrate, and hold on to their atmospheres. By stretching the limits of what a giant planet can be, these objects test the edges of our models. If a planet can be both Jupiter-sized and cotton-candy-light, then nature has more room to surprise us than our textbooks allow.