Astronomers confirm two super-puff planets less dense than cotton candy
9 reported
An international team led by the University of Oxford has confirmed two rare "super-puff" planets with densities lower than cotton candy. The planets, designated TOI-791 b and TOI-791 c, orbit an F7-type dwarf star about 1,110 light years from Earth in the southern constellation Volans. Each planet is about the size of Jupiter but remarkably lightweight, with TOI-791 b having a density of 0.038 grams per cubic centimeter and TOI-791 c measuring 0.047 grams per cubic centimeter. By comparison, Jupiter's average density is 1.33 grams per cubic centimeter, making it roughly 28 to 35 times denser. The findings were published in Monthly Notices of the Royal Astronomical Society. The planets were first flagged by citizen scientists in the Planet Hunters TESS project in 2019 and 2023, and confirmed using eight years of observations including data from the ASTEP telescope in Antarctica. The planets are linked by a 5:3 mean-motion resonance, and only four other planetary systems are known to contain multiple super-puff planets.
What’s reported
The two planets are TOI-791 b and TOI-791 c, orbiting an F7-type dwarf star about 1,110 light years from Earth in the constellation Volans.
TOI-791 b has a density of 0.038 grams per cubic centimeter; TOI-791 c has a density of 0.047 grams per cubic centimeter.
Jupiter's average density is 1.33 grams per cubic centimeter, making it 28 to 35 times denser than these planets.
Cotton candy has a typical density of about 0.05 grams per cubic centimeter.
The planets are in a 5:3 mean-motion resonance: for every five orbits of the inner planet, the outer planet completes nearly three.
Only four other planetary systems are known to contain multiple super-puff planets.
Citizen scientists flagged TOI-791 b in 2019 and TOI-791 c in 2023 via the Planet Hunters TESS project.
The ASTEP telescope in Antarctica observed the planets' transits, each lasting more than 11 hours.
The study was published in Monthly Notices of the Royal Astronomical Society.
Key figures
Dr. George Dransfield (she/her), lead author, Department of Physics, University of Oxford and presenter for BBC Sky at Night
Professor Amaury Triaud, University of Birmingham, UK Principal Investigator of ASTEP and co-author
Professor Tristan Guillot, Université Côte d'Azur, Principal Investigator of ASTEP and co-author
Sources: ScienceDaily
