NASA’s Transiting Exoplanet Survey Satellite (TESS) has identified two “super-puff” exoplanets, TOI-791 b and TOI-791 c, orbiting a solar-type star 1,113 light-years from Earth. These gas giants possess densities comparable to cotton candy, with masses less than 5% of Jupiter despite their immense physical size, challenging current models of planetary formation and atmospheric evolution.
The Physics of Low-Density Gas Giants
The discovery of TOI-791 b and c presents a significant anomaly for astrophysicists. While both planets are roughly the size of Jupiter, their mass is remarkably low. According to data confirmed by the TESS mission, TOI-791 b retains only 3% of Jupiter’s mass, while the slightly larger TOI-791 c accounts for just 5.9% of the mass of Jupiter. This disparity creates a density profile so light that researchers have categorized them as “super-puffs.”
The detection was made possible by the extended observation window provided by the TESS mission. Over a seven-year period, the satellite captured 1,122 days of photometric data, recording the repeated dimming of the host star as these bodies transited its disk. This long-baseline observation is critical for confirming long-period orbits; TOI-791 b completes an orbit in 139 days, while TOI-791 c takes 232 days.
Gravitational Coupling and Mass Verification
Beyond their physical dimensions, these planets exhibit a complex gravitational relationship. Analysis published in the Monthly Notices of the Royal Astronomical Society indicates that the two planets are locked in a mutual gravitational dance. As they orbit their host star, the planets alternate in their mutual attraction, affecting the timing of their transits across the host star. This allowed the research team to calculate the planets’ masses, confirming their status as low-density “super-puffs.”
"Only a few such super-puff planets are known, and it is even rarer to find two in the same system," Dransfield stated. The team’s collaboration included researchers from the Université Côte d’Azur/Observatoire de la Côte d’Azur and the University of Birmingham, utilizing the TESS data processed by the Science Processing Operations Center (SPOC) at NASA’s Ames Research Center.
Why These “Cotton Candy” Worlds Disrupt Planetary Models
The existence of these planets forces a re-evaluation of how gas giants accumulate mass and maintain their atmospheric volume. The “fluffy” nature of these worlds suggests they may have undergone a unique migration history or experienced atmospheric heating that keeps their gaseous envelopes extended.
Jon Jenkins, responsible científico of the SPOC at NASA’s Ames Research Center, emphasizes the investigative challenge: “They represent an enigma that we have to solve regarding how giant planets like Jupiter and the super-puffs form.”
- TOI-791 b: ~1 Jupiter radius; 3% Jupiter mass; 139-day orbital period.
- TOI-791 c: >1 Jupiter radius; 5.9% Jupiter mass; 232-day orbital period.
- Distance: 1,113 light-years from Earth.
- Primary Instrument: NASA TESS (Transiting Exoplanet Survey Satellite).
Future Objectives for Exoplanet Characterization
Understanding the chemical composition of these atmospheres is the next phase for the research collective. By analyzing how these planets rotate and how their orbital inclination aligns with the host star’s axis, scientists hope to determine how TOI-791 b and c migrated through the planetary system during their development, if their orbits were shaped by interactions with other planets and how low-density “super-puff” planets form. Steve Howell, a research scientist at NASA Ames, points out that the formation of such large-radius, low-mass bodies is likely a driver of overall system evolution.
The scientific community is now looking toward high-resolution spectroscopic follow-ups to detect trace elements within the atmospheres of TOI-791 b and c. Such data will be crucial to determining if these planets are truly “puffed up” by intense stellar radiation or if their low density is an intrinsic property of their formation cycle.
