Recent discoveries by a collaborative research team from Oxford, Côte d’Azur, and Birmingham universities have brought to light two captivating celestial bodies—TOI-791 b and TOI-791 c. These planets orbit the sun-like star TOI-791, located approximately 1,113 light-years away from Earth. What makes these two planets particularly extraordinary is their size, which is comparable to Jupiter, yet they possess only a fraction of his mass.
The study, published on June 24, 2026, in the Monthly Notices of the Royal Astronomical Society, introduces these “puffy” planets for the first time.
Unveiling TOI-791 b and TOI-791 c
The discovery of these planets was made possible through NASA’s Transiting Exoplanet Survey Satellite (TESS). Over a period of seven years, TESS monitored the star TOI-791 and detected the subtle changes in brightness that occur when a planet transits in front of its host star. Such observational data allowed researchers to identify these two distinct celestial bodies.
However, it’s not just their mere existence that captures attention; it’s their composition. According to a NASA press release, “TOI-791 b is nearly the size of Jupiter, yet it has only 3.0 percent of his mass. TOI-791 c is even larger than Jupiter but comprises only 5.9 percent of his mass.” The density of both planets is comparable to that of cotton candy, which is exceptionally low for planets of their size.
The Puffy Planets: A Unique Classification
While other low-density planets have been discovered before, TOI-791 b and TOI-791 c are noted as the “puffiest” ever found by NASA, falling into the category termed “Super-Puffs.” This classification highlights their extraordinary physical characteristics and challenges the prevailing understanding of planetary formation and structure.
Unusual Orbits and Density Confirmation
One intriguing aspect of TOI-791 b and c is how their orbits contribute to our understanding of their density. The analysis of TESS data revealed that the planets are in an orbit that allows them to exert gravitational influence on each other. This gravitational interaction leads to variations in their transit timings, thereby providing scientists with crucial data to calculate their masses accurately.
George Dansfield, the lead author of the study and a physicist at Oxford University, remarked, “Only a few of these extremely inflated planets are known, and it’s even rarer to find two in the same system. Their extraordinarily low density makes them fascinating research subjects for understanding how planetary systems form and evolve.”
Significance of Large Planets in Planetary System Development
The research team aims to further investigate various attributes of these planets, such as the chemical composition of their atmospheres, the effects of their rotation on their shapes, and the inclination of their host star relative to their orbits. As co-author Steve Howell explains, “The formation of large planets is believed to drive the development of planetary systems,” making the study of these Jupiter-sized but significantly less massive planets invaluable.
Overall, the discovery of TOI-791 b and c not only enriches our library of known exoplanets but also opens new avenues for research into the dynamics of planetary systems. As we continue to explore our universe, each discovery serves as a stepping stone toward a deeper understanding of the cosmos.
Originally published on June 26, 2026, this article remains of high interest, prompting an update to share these groundbreaking findings once more.
