Astronomers Discover Two Of The Puffiest Planets Ever Each As Big As Jupiter But Lighter Than Cotton Candy

Astronomers have discovered two giant super-puff exoplanets as big as Jupiter but lighter than cotton candy. The rare worlds have the lowest densities ever measured for planets of their size, offering scientists a new opportunity to understand how giant planets form and evolve. The findings were published in Monthly Notices of the Royal Astronomical Society on Wednesday, June 24. Giant planets with the density of cotton candyThe newly discovered planets, TOI-791 b and TOI-791 c, orbit the Sun-like star TOI-791, located about 1,110 light-years from Earth in the southern constellation Volans. Although both planets are roughly the size of Jupiter, they contain only a tiny fraction of Jupiter's mass, giving them astonishingly low densities.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. For comparison, cotton candy has a density of about 0.05 grams per cubic centimeter. Jupiter's average density is 1.33 grams per cubic centimeter. Earth's density is approximately 5.5 grams per cubic centimeter.NASA described the pair as the puffiest planets ever found, while researchers say they are among the lowest-density giant planets ever detected. Comparable to a nice blob of shaving foam Lead author Dr George Dransfield from the University of Oxford said the discovery surprised researchers. ‘Superpuffs are super rare; in fact, we have discovered only 37 other superpuffs so far,’ she explained in a social media post. Describing just how light these worlds are, Dr Dransfield added: These two planets have densities comparable to a nice blob of shaving foam, fresh from the can. NASA scientist Jon Jenkins, science lead for the Science Processing Operations Center at NASA's Ames Research Center, said the discovery challenges existing theories of planet formation. The main reason these planets are interesting to study is that we didn't expect to see them at all. They represent a puzzle for us to solve about how giant planets like Jupiter and the super-puffs form. Discovered after years of observationsThe planets were first spotted by NASA's TESS mission, which searches for distant worlds by watching for tiny dips in a star's brightness as planets pass in front of it. TOI-791 b was first identified as a candidate planet in 2019, while TOI-791 c followed in 2023 through the Planet Hunters TESS citizen-science project.Researchers then spent eight years gathering observations from telescopes across the globe, including the ASTEP (Antarctic Search for Transiting ExoPlanets) telescope at Concordia Station in Antarctica.The Antarctic winter provided months of uninterrupted darkness, allowing astronomers to observe planetary transits lasting more than 11 hours, the longest continuous planetary transits ever recorded from the ground.Locked together in a rare orbital danceThe two planets are believed to have formed from the same disc of gas and dust surrounding their young star. They are also locked in a rare 5:3 mean-motion resonance, meaning that for every five orbits completed by TOI-791 b, TOI-791 c completes almost exactly three.Their repeated gravitational tugs slightly alter the timing of each transit, enabling scientists to calculate their masses and confirm their remarkably low densities.Only four other planetary systems are currently known to contain multiple super-puff planets, making TOI-791 an unusually valuable system for studying planetary evolution.Why are these planets so light?Astronomers are still debating how super-puff planets form. One leading theory suggests they possess enormous hydrogen- and helium-rich atmospheres that account for much of their size despite their small mass. These giant gaseous envelopes may have formed far from their host star, where colder conditions allowed gas to accumulate rapidly around a solid planetary core.The planets also have unusually long years. TOI-791 b completes one orbit every 139 days, while TOI-791 c takes 232 days, making them among the longest-orbiting super-puff planets discovered.James Webb Space Telescope could reveal moreScientists now hope to study the planets using NASA's James Webb Space Telescope to determine the composition of their unusually inflated atmospheres.Future observations may reveal whether their atmospheres contain carbon, nitrogen, and oxygen-bearing molecules while also helping researchers understand how these giant worlds formed and migrated through their planetary system.