NASA's TESS Finds Rare 'Super-Puff' Planetary Pair 1,113 Light-Years Away
Two exceptionally low-density exoplanets orbiting a single star challenge existing models of gas giant formation.
NASA's Transiting Exoplanet Survey Satellite (TESS) mission has identified two "super-puff" exoplanets, TOI-791 b and TOI-791 c, orbiting a distant Sun-like star. The discovery of two such low-density worlds within a single system is an exceptionally rare find that provides a new window into the diversity of planetary structures.
Located approximately 1,113 light-years from Earth, the planets orbit the star TOI-791. Both worlds are comparable in size to Jupiter but possess only a tiny fraction of its mass, resulting in densities that astronomers have compared to cotton candy. Specifically, TOI-791 b is nearly the size of Jupiter but contains only about 3% of its mass. Its companion, TOI-791 c, is even larger than Jupiter, yet it holds only approximately 5.9% of Jupiter's mass.
The Nature of Super-Puffs
Super-puff planets represent a rare class of exoplanets defined by their massive radii paired with extremely low masses. While astronomers have identified a small number of these objects in the past, they remain anomalies in the broader catalog of known worlds. Most gas giants follow a more predictable relationship between size and mass; however, super-puffs defy these norms, existing as bloated spheres of gas with very little solid core material to anchor them.
Finding two of these planets in the same system is significantly rarer than finding a single isolated super-puff. This pairing suggests that the conditions required to create such low-density worlds may be systemic rather than accidental, offering a controlled environment for researchers to study the variables that lead to this specific planetary morphology.
Implications for Planetary Science
The extreme low density of TOI-791 b and c provides critical data for understanding the mechanisms of planetary formation and evolution. Because these worlds challenge standard models of how gas giants are structured, they force scientists to reconsider how atmospheres are retained and how planets migrate within their early solar systems.
George Dransfield, lead author from Oxford University’s Department of Physics, noted that only a handful of these super-puffy planets are known. He emphasized that their extremely low densities make them fascinating targets for understanding how planetary systems form and evolve, as they represent an extreme edge of what is physically possible for a planet.
Future Observations
As these planets are now confirmed, they will likely become primary targets for follow-up observations using more powerful telescopes. Astronomers will seek to determine the exact chemical composition of their atmospheres to understand what allows them to remain so expanded without dissipating into space. While the core physical properties are established, the specific atmospheric makeup and the precise interaction between the two planets remain the next frontiers for the research team.