An international research team led by the University of Oxford has discovered two rare “super-puff” planets, TOI-791 b and TOI-791 c, which possess densities lower than candy floss. Located 1,110 light-years away in the constellation Volans, these Jupiter-sized worlds provide scientists with a unique opportunity to study the limits of planetary gas retention and formation.
How dense are the TOI-791 planets?
The two planets, TOI-791 b and TOI-791 c, orbit an F7-type dwarf star and exhibit extremely low mass-to-volume ratios. According to research published in Monthly Notices of the Royal Astronomical Society, TOI-791 b has a density of just 0.038 grams per cubic centimetre. Its sibling, TOI-791 c, follows closely with a density of 0.047 grams per cubic centimetre.
To put these figures into perspective, the density of Jupiter sits at approximately 1.33 grams per cubic centimetre. This makes the new planets roughly 28 to 35 times lighter than Jupiter for their size. Even candy floss, which typically has a density of about 0.05 grams per cubic centimetre, is technically denser than these two celestial bodies.
While these planets are nearly the same size as Jupiter, they are so diffuse that lead researcher Dr. George Dransfield compared their density to a fresh blob of shaving foam.
How were these “super-puff” worlds discovered?
The discovery began with human intuition rather than automated algorithms alone. Candidates for the planets were first flagged in 2019 and 2023 by volunteers participating in the Planet Hunters TESS citizen-science project. These volunteers combed through data from NASA’s Transiting Exoplanet Survey Satellite, looking for the specific dips in starlight that occur when a planet passes in front of its host star.
Following these initial sightings, professional astronomers used a telescope stationed in Antarctica to confirm the findings. The Antarctic location provides exceptionally long, dark nights, allowing for the high-precision data collection necessary to measure the planets’ masses and sizes. By combining these measurements, the team calculated the exact density of the gas surrounding the planets.
Why does this discovery matter for planetary science?
Finding two such low-density planets in a single system is an anomaly. Dr. George Dransfield, currently at the University of Oxford and formerly at the University of Birmingham, stated that only a handful of these “super-puffy” planets are known to exist. Finding two sharing the same star is significantly rarer.
Professor Amaury Triaud from the University of Birmingham, the project’s UK Principal Investigator, described the TOI-791 system as a “unique laboratory.” The study suggests both planets likely formed from the same disc of gas and dust surrounding their young star. This shared origin helps researchers understand why some giant planets become dense and compact like Jupiter, while others remain loosely packed for billions of years.
Frequently Asked Questions
How far away is the TOI-791 system?
The system is located approximately 1,110 light-years from Earth in the southern constellation Volans.
What is a “super-puff” planet?
A super-puff planet is a gas giant that has a large physical size but an extremely low density, meaning it is composed of very spread-out gas.
Are these planets habitable?
No. These are gas giants with extremely low densities, making them vastly different from rocky, Earth-like planets.
What do you think about these “candy floss” planets? Could there be more hidden in our galaxy? Let us know your thoughts in the comments below or subscribe to our newsletter for more space exploration updates.