Two newly discovered exoplanets, TOI-791b and TOI-791c, resemble Jupiter in size but are remarkably less dense than cotton candy. This discovery offers astronomers a unique opportunity to understand the formation and evolution of gas giant planets.
Diagram showing TOI-791b and TOI-791c alongside their parent stars. Image credit: NASA/Daniel Rutter.
TOI-791b matches Jupiter’s size but contains only 3% of its mass, while TOI-791c is even larger and holds just 5.9% of Jupiter’s mass.
Both exoplanets orbit a sun-like star called TOI-791, located approximately 1,113 light-years away in the constellation Taurus.
“The primary reason these planets intrigue us is that their existence defies expectations,” said Dr. John Jenkins of NASA’s Ames Research Center.
“They present a key puzzle in understanding the formation of giant planets like Jupiter and their evolution,” he added.
NASA’s TESS mission identified these exoplanets through the observation of periodic dips in the luminosity of the star, indicating planetary transits.
Due to their lengthy orbital periods (139 days for TOI-791b and 232 days for TOI-791c), TESS compiled 1,122 days of observations over seven years to confirm their characteristics.
“This system serves as a distinctive laboratory for exploring the formation and evolution of superpuff planets,” stated Professor Amaury Tryode from the University of Birmingham.
“We aim to utilize NASA/ESA/CSA’s James Webb Space Telescope for space-based observations to determine whether the inflated atmospheres contain molecules of carbon, nitrogen, and oxygen, providing new insights into their formation,” he added.
Comparison of TOI-791b and TOI-791c to some planets in our solar system. Image credit: NASA/Daniel Rutter.
TOI-791b and TOI-791c are gravitationally locked in an orbital dance, subtly influencing the timing of their transits.
Astronomers measured these timing variations to accurately calculate the planets’ masses, revealing their unusually low densities.
“Only a few super-bulky planets like these exist, and finding two within the same system is extremely rare,” emphasized Dr. George Dunsfield from the University of Oxford.
“Their low densities make them fascinating subjects for understanding the formation and evolution of planetary systems,” he continued.
“Further investigations into these Jupiter-sized yet less massive planets are invaluable, as the emergence of large planets is believed to significantly impact the evolution of planetary systems,” noted Steve Howell, a researcher at NASA’s Ames Research Center.
Professor Tristan Guillot from the University of the Cote d’Azur stated, “These multiplanetary systems experience complex gravitational interactions, evolving over decades.”
This significant finding is detailed in a recent article: paper published in Royal Astronomical Society Monthly Notices.
_____
Georgina Dransfield et al. 2026. ASTEP identified a pair of long-period, Jupiter-sized planets with extremely low density orbiting TOI-791. MNRAS 549 (4): stag864;doi: 10.1093/mnras/stag864
Source: www.sci.news
