Cotton Candy Is Denser Than Some Planets

Astronomers have found two giant planets, each roughly the size of Jupiter, with densities so low they fall below that of spun sugar. That is not a metaphor chosen for effect. Cotton candy has a density of about 0.05 grams per cubic centimeter. TOI-791 b comes in at 0.038 grams per cubic centimeter, and TOI-791 c at 0.047. The planets are, technically, less substantial than a fairground snack.

Volunteer Planet Hunters first identified the planets in 2019 and 2023 while searching data from NASA's Transiting Exoplanet Survey Satellite for possible new worlds. Now a research team, led by the University of Oxford in collaboration with Université Côte d'Azur and the University of Birmingham, has confirmed that rare super-puff giant planets are orbiting an F7-type dwarf star about 1,110 light-years from Earth.

This system features a combination of oddities stacked inside it. The inner planet circles the star five times for every three orbits of the outer planet, causing the planets to tug on each other in ways astronomers can measure. Only a few systems like this are known, and very few contain more than one super-puff planet. Scientists aren’t sure how these extremely low-density worlds form, but one idea is that they formed far from their star, where it was cool enough to collect huge, hydrogen-rich atmospheres before moving inward.

Researchers plan to use the James Webb Space Telescope to look for carbon-, nitrogen-, and oxygen-containing molecules in the planets’ atmospheres. Detecting these chemicals could help explain where the planets formed and how they became so unusually puffy.

Out of nearly 6,300 confirmed exoplanets listed by NASA, fewer than 40 are classified as super-puffs. Finding two in the same system, locked in gravitational step with each other, is the kind of find that tends to outlast the press release.

Read the full story at Discover Magazine, June 25, 2026

Hot Take:Cotton-candy-density planets sound whimsical, but “super-puff planets” feel less like a category and more like physics quietly shrugging and rebranding a bug as a feature.