Scientists have discovered two enormous planets that are surprisingly light, similar to cotton candy. These planets, named TOI-791 b and TOI-791 c, are located in the constellation Volans, about 1,110 light-years away. They are as big as Jupiter but have much less mass, making them incredibly low in density. In fact, they are less dense than cotton candy, which has a density of about 0.05 grams per cubic centimeter. The inner planet has a density of 0.038 g/cm³, and the outer one is 0.047 g/cm³. For comparison, Jupiter is 28 to 35 times denser.
Physicist George Dransfield from the University of Oxford described their density as being like shaving foam. Finding such planets, known as "super-puffs," is rare. Out of thousands of known exoplanets, fewer than 40 are super-puffs, and finding two in the same star system is even more unusual.
The discovery began with amateur astronomers in the Planet Hunters TESS project who noticed odd patterns in satellite data in 2019 and 2023. Professional astronomers then used data from NASA's Transiting Exoplanet Survey Satellite and the ASTEP telescope in Antarctica to confirm their existence. The planets orbit their star in a synchronized way, with the inner planet taking 139 days and the outer one 232 days for a full orbit. Their gravitational pull on each other causes slight shifts in their orbits, which helped scientists calculate their mass and confirm their low density. The transits, when the planets pass in front of their star, are unusually long, lasting over 11 hours.
These planets, likely made of hydrogen and helium, challenge current theories of planet formation. Researchers plan to use the James Webb Space Telescope to study their composition further.