Astronomers Confirm Two Super-Puff Planets

Astronomers have confirmed the discovery of two of the least dense planets ever found, giant worlds so light and airy they are less dense than cotton candy. The planets, designated TOI791 b and TOI791 c, orbit a star approximately 1,110 light-years from Earth in the southern constellation Volans. The findings, published on June 25 in the journal Monthly Notices of the Royal Astronomical Society, detail an exceptionally rare system that offers new insights into planetary formation.

Both planets are roughly the size of Jupiter but contain far less mass. TOI791 b has a density of 0.038 grams per cubic centimeter, while TOI791 c has a density of 0.047 grams per cubic centimeter. For comparison, Jupiter's average density is 1.33 grams per cubic centimeter, and cotton candy is about 0.05 grams per cubic centimeter. The planets are believed to be siblings that formed together from the same disk of gas and dust surrounding their young star.

The discovery relied on an international collaboration and data spanning eight years. The planets were first flagged as candidates by volunteers with the Planet Hunters TESS citizen science project, which analyzes data from NASA's Transiting...