Astronomers discover pair of cotton-candy light super-puff planets

Astronomers identified a pair of Jupiter-sized super-puffs orbiting TOI-791, a star about 1,113 light-years from Earth in the southern constellation Volans. The two planets, TOI-791 b and TOI-791 c, are so low in density that NASA described them as the puffiest planets ever found, a rarity that puts familiar ideas about planet formation under strain.

The planets were first flagged by NASA’s Transiting Exoplanet Survey Satellite and then measured more precisely with telescopes on Earth. TOI-791 b circles its star every 139.29931 days, while TOI-791 c takes 232.01570 days. The study describes both worlds as long-period, dynamically interacting, transiting Jupiter-sized planets with extremely low densities around an F7 dwarf star. Their orbits sit within 0.07 percent of a second-order 5:3 period commensurability, and that close resonance produces transit-timing variations of up to 50 minutes.

That orbital tugging is part of what makes the system especially valuable. The low density suggests the planets are dominated by hydrogen and helium, but their exact chemical makeup remains unsettled. Follow-up observations with Webb are expected to probe their atmospheres more closely and test how much gas the planets still retain after years of stellar radiation and internal evolution. The visual shorthand is memorable, with George Dransfield of the University of Oxford comparing the planets’ wispy makeup to a blob of shaving foam fresh from the can, but the scientific value is sharper than the metaphor.

Dransfield, a Fellow by Examination in Physics at Magdalen College, Oxford, said work on exotic systems adds pieces to the broader puzzle of planet formation and helps scientists learn more about Earth’s place in the cosmos. His Oxford profile lists giant planets, low-mass stars and exoplanet detection among his research interests. The discovery also lands in a sparse corner of the exoplanet catalog: fewer than 40 super-puffs are known among nearly 6,300 confirmed worlds outside the solar system, while NASA’s catalog now contains more than 6,000 confirmed exoplanets.

That scarcity is what gives TOI-791 b and TOI-791 c their force as a test case. A recent arXiv paper has argued that cold super-puffs remain difficult to explain under core-accretion theory, even as some short-period cases may be shaped by irradiation and star-planet interactions. The new pair broadens the sample astronomers can study, and it sharpens the questions around how giant planets form, how they lose material, and how some of them survive in such an inflated state.