A pair of 'super-puff planets' lighter than shaving foam or cotton candy have been discovered, researchers told Metro. TOI-791 b and TOI-791 c are exoplanets located 1,100 light-years from Earth. Despite being the size of Jupiter, they are not celestial heavyweights—they are what scientists call 'super-puff' planets.
Remarkably Low Densities
Jupiter has a density 28 times greater than TOI-791 c and 35 times greater than TOI-791 b, according to a paper published in the Monthly Notices of the Royal Astronomical Society. Lead author Dr. George Dransfield, an astrophysicist at the University of Oxford, told Metro: 'They also have a similar density to shaving foam. At least shaving foam is white, not pink, and doesn’t taste nice. So people aren’t just thinking, “oh, tasty planets.”'
Discovery and Observations
Dr. Dransfield and her team used observations from the Antarctic Search for Transiting ExoPlanets telescope at Concordia Station in Antarctica. She described the station as almost like being on an alien world: 'There’s no life, there’s no microbes, there’s no birds, there’s no nothing. Nothing can live there because it’s so cold and so dry.'
Inhospitable Worlds
If Earth were as fluffy as TOI-791 b or TOI-791 c, it would be 'devoid of all life,' said Dr. Dransfield. 'There would be no solid surface to speak of and these planets are less dense than water, so they would float in almost any liquid. I don’t know how you’d be able to get life going on these floating balls of gas.'
Rarity of Super-Puffs
Fewer than 37 of the 6,300 exoplanets discovered so far are super-puffs. Dr. Dransfield added: 'Only four other systems contain multiple super-puffs in the same system. It’s a really rare configuration.'
How They Were Identified
TOI-791 b and TOI-791 c orbit a yellow-white dwarf star slightly brighter and hotter than the Sun. When an exoplanet passes in front of its host star, its atmosphere is backlit—a moment called transit. By analyzing changes in starlight, scientists guess the planet’s chemical makeup. Researchers think their atmospheres may be filled with featherweight hydrogen and helium. The planets' densities were estimated by how their gravities affect each other, altering transit times.
Formation Theories
TOI-791 b and TOI-791 c may have formed far from the star in a cooler region. Dr. Dransfield explained: 'Somehow these planets got away with not having a core 10 times the mass of Earth because there’s so much gas there. They must have had a significantly smaller core. One thing that we think might be happening is they’re forming in a region of the disc where there’s a lot more gas available than solids, so that they can start grabbing gas.'
Further Observations
TOI-791 b and TOI-791 c were identified in 2019 and 2023, respectively, by the Planet Hunters citizen scientist group using NASA data. They have a rare mean-motion resonance: for every five orbits of the inner planet, the outer completes roughly three. Astronomers found that their transits can last up to 11 hours, charted thanks to Antarctica's darkness. Dr. Dransfield added that the star's behavior is 'awkward,' but such comparisons help make these rare and weird worlds easier to grasp.
