Full Breakdown
Super-Puff Siblings: Two Jupiter-Sized Worlds Lighter Than Cotton Candy
6/26/2026, 11:13:36 AM
Discovery of Two Super-Puff Exoplanets
Astronomers using NASA’s TESS data and follow-up ground observations confirmed two Jupiter-sized exoplanets, TOI-791 b and TOI-791 c, orbiting the Sun-like star TOI-791 in Volans at ~1,110 light-years.
Background & Rarity
Super-puff planets—giant worlds with densities lower than cotton candy—are rare; fewer than 40 are known among ~6,300 confirmed exoplanets, and only four systems host multiple super-puffs.
Research Team
The work was led by George Dransfield (University of Oxford) with co-authors Jon Jenkins (NASA Ames), Steve Howell (NASA), Amaury Triaud (University of Birmingham) and Tristan Guillot, in collaboration with Université Côte d’Azur and the University of Birmingham.
Physical Characteristics
Both planets are Jupiter-sized; TOI-791 b has ~3 % of Jupiter’s mass and a density of 0.038 g cm?³, while TOI-791 c has ~5.9 % of Jupiter’s mass and a density of 0.047 g cm?³. Their orbital periods are 139 days and 232 days, forming a 5:3 mean-motion resonance that produces measurable transit-timing variations.
Why It Matters
The unusually low densities challenge standard giant-planet formation models and provide a rare laboratory for testing theories of rapid hydrogen-helium accretion in cold protoplanetary disks.
Official Statements & Responses
Dransfield described the planets as having densities “comparable to a nice blob of shaving foam,” while Jenkins said they “represent a puzzle for us to solve about how giant planets like Jupiter and the super-puffs form.” NASA noted that the discovery adds “further pieces to the puzzle of planet formation” and that the exoplanet catalog now includes nearly 6,300 worlds, fewer than 40 of which are super-puffs.
Criticism & Ongoing Debate
Some scientists argue that alternative pathways—such as late-stage atmospheric loss or migration from farther out—could also produce super-puffs, and they stress that atmospheric composition remains unconfirmed pending JWST observations.
Conflicting Reports & Gaps
The star’s distance is reported as 1,110 ly in some sources and 1,113 ly in others; Jupiter’s density is quoted as 28-times or 35-times greater than the planets, reflecting minor rounding; and the planets’ atmospheric makeup is still unknown.
Verbatim Quotes
- “These two planets have densities comparable to a nice blob of shaving foam, fresh from the can,” — George Dransfield, University of Oxford
- “The main reason these planets are interesting to study is that we didn't expect to see them at all,” — Jon Jenkins, NASA Ames Research Center
- “This system offers a unique laboratory for understanding how super-puff planets form and evolve,” — Amaury Triaud, University of Birmingham
- “These multi-planetary systems are complex, with gravitational interactions between the planets that evolve over very long periods, tens of years or more,” — Tristan Guillot, co-author
What’s Next
The team plans JWST spectroscopy to detect carbon, nitrogen and oxygen species in the atmospheres, and continued transit-timing monitoring to refine the planets’ orbital dynamics.
