Full Breakdown
Two Super-Puff Exoplanets Discovered Orbiting a Distant Dwarf Star
6/29/2026, 11:01:17 AM
Discovery of the TOI-791 Super-Puff Pair
Astronomers discovered two giant exoplanets, TOI-791b and TOI-791c, orbiting a dwarf star 1,110 light-years away in the constellation Volans. The planets were first identified in NASA’s TESS data by volunteers in the Planet Hunters citizen-science project, and their unusually long, >11-hour transits signaled their presence.
Formation Context
Super-puff planets have bulk densities lower than cotton candy. The prevailing hypothesis holds they are enveloped in massive hydrogen-helium atmospheres surrounding small rocky cores formed in the cold outer disc.
Observational Campaign
Following the TESS detection, the team measured transit timing variations to derive planetary masses. Because each transit lasts over eleven hours, continuous monitoring was required. The ASTEP telescope at Concordia Station captured full transits during the Antarctic winter, providing the longest uninterrupted ground-based observations of any exoplanet to date.
Physical Properties
Both planets have radii comparable to Jupiter but densities of 0.038 g cm?³ (TOI-791b) and 0.047 g cm?³ (TOI-791c), 28–35 times less dense than Jupiter and below cotton-candy density. Their orbital periods are locked in a 5:3 mean-motion resonance, producing measurable timing shifts.
Scientific Significance
The rarity of super-puff planets—only a few are known—and the even rarer occurrence of two in one system make the TOI-791 pair a crucial test of atmospheric inflation and core-mass theories, potentially reshaping models of gas accretion in young planetary systems.
Official Statements
Dr. George Dransfield highlighted the scarcity of comparable systems, noting that only a handful of super-puff planets are known and finding two together is exceptionally rare. Prof. Tristan Guillot emphasized the essential role of multi-continental observations, while Prof. Amaury Triaud outlined a JWST proposal to detect carbon, nitrogen, and oxygen gases and clarify formation pathways.
Ongoing Debate and Knowledge Gaps
The hydrogen-helium envelope hypothesis remains unproven; alternative explanations such as delayed cooling or high atmospheric opacity have not been excluded, and further spectroscopic data are needed to discriminate among models.
Verbatim Quotes
- “Only a handful of these super-puffy planets are known, and it is even rarer to find two in the same system,” — Dr. George Dransfield, Lead Author, University of Oxford
- “Bringing together observations from Antarctica, space telescopes, and observatories across several continents was essential to revealing the true nature of these extraordinary planets,” — Prof. Tristan Guillot, Co-author, Université Côte d’Azur
- “We propose to carry out space-based observations using the James Webb Space Telescope to assess if the puffy atmosphere contains carbon-, nitrogen-, and oxygen-bearing species, revealing new insight into how these unusual planets formed,” — Prof. Amaury Triaud, Co-author, University of Birmingham
- “They are, in effect, planet shaped clouds.” — The research team (University of Oxford, University of Birmingham, Université Côte d’Azur)
Future Observations
The team plans to request JWST time to obtain transmission spectra of both planets, aiming to detect atmospheric constituents and test the hydrogen-helium envelope model, thereby refining formation theories for super-puff worlds.
