Astronomers Found Two Rare Super Puff Planets Lighter Than Cotton Candy

Astronomers have identified two of the fluffiest giant planets ever discovered. The planets, designated TOI-791 b and TOI-791 c, orbit an F7-type dwarf star about 1,110 light years from Earth in the southern constellation Volans. Each planet is about the size of Jupiter but has an extraordinarily low density. TOI-791 b has a density of just 0.038 grams per cubic centimeter, while TOI-791 c measures 0.047 grams per cubic centimeter. Jupiter, by comparison, has an average density of 1.33 grams per cubic centimeter. Candy floss has a typical density of about 0.05 grams per cubic centimeter. The findings were led by an international team from the University of Oxford, in collaboration with Université Côte d'Azur/Observatoire de la Côte d'Azur and the University of Birmingham. The results were published June 26, 2026, in Monthly Notices of the Royal Astronomical Society. The planets are linked by a 5:3 mean-motion resonance. Volunteers participating in the Planet Hunters TESS citizen-science project first flagged the candidates. Observations drew on eight years of data, including measurements from the ASTEP telescope at Concordia Station in Antarctica, where the planets' transits, each lasting more than 11 hours, were recorded without interruption. Lead author Dr. George Dransfield of the University of Oxford said: "Only a handful of these super-puffy planets are known, and it is even rarer to find two in the same system. Their extremely low densities make them fascinating targets for understanding how planetary systems form and evolve."