Astronomers have identified two incredibly light "super-puff" planets with densities lower than cotton candy, offering new insights into planetary formation.
Astronomers have made a remarkable discovery of two exceptionally lightweight giant planets, known as "super-puffs," with densities so low they rival that of cotton candy. This extraordinary find, led by an international team from the University of Oxford in collaboration with Université Côte d'Azur/Observatoire de la Côte d'Azur and the University of Birmingham, has been published in the Monthly Notices of the Royal Astronomical Society.
The two newly confirmed planets, TOI-791 b and TOI-791 c, orbit an F7-type dwarf star located roughly 1,110 light years away in the southern constellation Volans. Despite being comparable in size to Jupiter, both planets exhibit surprisingly low densities: TOI-791 b has a density of just 0.038 grams per cubic centimeter, while TOI-791 c is slightly denser at 0.047 grams per cubic centimeter. For comparison, Jupiter has an average density of about 1.33 grams per cubic centimeter, making it roughly 28 to 35 times denser than these super-puff planets.
To illustrate their unusual lightness, candy floss has a typical density of about 0.05 grams per cubic centimeter, while Earth is much denser, averaging 5.5 grams per cubic centimeter. This distinctively low density raises intriguing questions about the formation and evolution of such planets.
Gravitational Dance of Unique Planetary Twins
Researchers believe that TOI-791 b and c formed together from the same disc of gas and dust surrounding their young star, marking them as planetary siblings. These planets are entwined in a peculiar orbital arrangement characterized by a 5:3 mean-motion resonance. This means that for every five orbits completed by the inner planet, the outer planet completes nearly three. Their gravitational pull influences each other's orbits, leading to measurable variations in the timing of their transits.
Notably, only four other planetary systems are known to host multiple super-puff planets, making TOI-791 a rare opportunity to explore the characteristics and origins of these unusual worlds.
Lead author Dr. George Dransfield from the University of Oxford remarked on the significance of this discovery: "Only a handful of these super-puffy planets are known, and it is even rarer to find two in the same system. Their extremely low densities make them fascinating targets for understanding how planetary systems form and evolve."
Citizen Science and Global Collaboration
The discoveries of TOI-791 b and c emerged from the Planet Hunters TESS citizen-science project, which highlighted TOI-791 b in 2019 and TOI-791 c in 2023 as potential planets. This project diligently analyzes data collected by NASA's Transiting Exoplanet Survey Satellite (TESS) in search of unknown worlds.
Following the identification of these planets, a combination of measurements from various telescopes helped determine their sizes and masses, ultimately revealing their surprisingly low densities. The observational technique involved monitoring the transits, where a planet crosses in front of its star and temporarily blocks starlight, leading to a detectable dip in brightness. Furthermore, astronomers noted slight timing changes in these transits caused by the gravitational interactions between the two planets, aiding in mass estimation.
This investigation was fueled by eight years of observational data, including insights from the ASTEP (Antarctic Search for Transiting ExoPlanets) telescope located at Concordia Station in Antarctica. The unique geographic location provided astronomers with months of uninterrupted darkness, facilitating the observation of the planets' lengthy transits, each exceeding 11 hours—marking the longest continuous planetary transits ever observed from the ground.
Understanding Super-Puff Planets
There is ongoing research into how super-puff planets like TOI-791 b and c come to be. One prevailing theory suggests these planets possess massive atmospheres primarily comprised of hydrogen and helium, constituting a significant portion of their total mass. Researchers propose that these thick atmospheres may have developed when the planets resided in cooler regions of the protoplanetary disc, allowing gas to accumulate around a solid core as they drifted farther from their star.
Future observational campaigns are planned to deepen our understanding of these unique planets and validate competing formation theories. Professor Amaury Triaud from the University of Birmingham, the UK Principal Investigator of ASTEP and co-author of the study, highlighted the potential of this system to serve as a laboratory for planetary formation analysis, stating, "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."
Professor Tristan Guillot from Université Côte d'Azur emphasized the complexity of multi-planetary systems: "These multi-planetary systems are complex, with gravitational interactions between the planets that evolve over very long periods. This discovery underlines the importance of continued international collaboration in astronomy," he noted, acknowledging the critical role shared observations played in uncovering the characteristics of these extraordinary planets.
Materials provided by University of Oxford. Note: Content may be edited for style and length.
Discussion
Sign in to join the discussion.