These Rare Super-Puff Planets Are Less Dense Than Cotton Candy
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Learn more about super-puff planets and how researchers determined the densities of these far-off planets.
Monica Cull is a Digital Editor/Writer for Discover Magazine who writes and edits articles focusing on animal sciences, ancient humans, national parks, and health trends. Using NASA’s TESS Space Telescope, an international research team has identified twin planets with densities lower than cotton candy. The research team, led by the University of Oxford, in collaboration with Université Côte d’Azur/Observatoire de la Côte d’Azur, and the University of Birmingham, detected the rare ‘super-puff’ giant planets orbiting an F7-type dwarf star that is about 1,110 light-years from Earth.
The planets, named TOI-791 b and TOI-791 c, are each about the size of Jupiter but are significantly less dense. Little is known about how ‘super-puff’ planets form, but this discovery could help fill in some gaps. The findings were published in Monthly Notices of the Royal Astronomical Society.
“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,” said lead author George Dransfield (she/her), from the University of Oxford and presenter for BBC Sky at Night, in a press release. TOI-791 b and TOI-791 c are siblings, according to the study, and likely formed together from the same disc of dust and gas that surrounded their star, which is located in the southern constellation of Volans.
Despite their size, TOI-791 b has a density of 0.038 grams per cubic centimeter, and TOI-791 c has a density of 0.047 grams per cubic centimeter. In comparison, Jupiter has a density of about 1.33 grams per cubic centimeter. More surprising is that the densities are lower than that of cotton candy, which has a density of about 0.05 grams per cubic centimeter.
Earth, on the other hand, has a density of about 5.5 grams per cubic centimeter. Based on the team's observations, these planets are also in a rare gravitational relationship — known as a 5:3 mean-motion resonance. This means that for every five orbits the inner planet makes, the outer planet makes about three.
This relationship results in the planets repeatedly tugging on one another, causing measurable shifts in their orbits.
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