Giant Planets That Barely Weigh Anything
Astronomers have identified two extraordinary exoplanets that challenge what scientists thought they knew about giant worlds. Named TOI-791 b and TOI-791 c, these newly confirmed planets are nearly as large as Jupiter but astonishingly light, making them the least dense gas giants ever discovered.
Located about 1,110 light-years from Earth in the constellation Volans, the planets orbit a Sun-like star. Their incredibly low densities are even lower than that of cotton candy, earning them the nickname “super-puff” planets. Scientists estimate that Jupiter is roughly 28 to 35 times denser than these unusual worlds.
A Rare Planetary Pair
Super-puff planets are among the rarest types of exoplanets known. Out of thousands of confirmed exoplanets, fewer than 40 belong to this category. Finding two super-puff planets in the same planetary system makes the discovery even more remarkable and offers researchers a unique opportunity to investigate how these strange worlds form and evolve.
The two planets also share an uncommon orbital relationship known as a 5:3 mean-motion resonance. This means that for every five orbits completed by the inner planet, the outer planet circles its star almost exactly three times. Their repeated gravitational interactions provide valuable clues about their history and internal structure.
Unlocking the Mystery of Planet Formation
Scientists believe TOI-791 b and TOI-791 c likely formed in the colder outer regions of their planetary system, where they accumulated enormous hydrogen and helium atmospheres around relatively small cores before gradually migrating closer to their host star. Their bloated atmospheres make them appear much larger than their actual mass would suggest.
The planets were first spotted by volunteers participating in NASA’s Planet Hunters TESS citizen-science project using observations from the Transiting Exoplanet Survey Satellite (TESS). Astronomers later confirmed their existence with ground-based telescopes, including the ASTEP telescope in Antarctica.
Researchers hope future observations with the James Webb Space Telescope will reveal the chemical makeup of these ultra-light atmospheres. Those findings could help explain why super-puff planets are so rare and provide new insights into how planetary systems develop across the galaxy.
