Super-Puff Planets Found Lighter Than Candyfloss

Two gas giant exoplanets, designated TOI-5205b and TOI-1214b, have been identified as having exceptionally low densities, placing them among the least dense planets ever discovered. These celestial bodies orbit the same star, a red dwarf located approximately 1,000 light-years from Earth. The findings were published online on July 9, 2026, in the journal Nature.

The density of TOI-5205b is calculated to be around 0.05 grams per cubic centimeter, which is significantly less dense than cotton candy (0.1 grams per cubic centimeter). Similarly, TOI-1214b exhibits a density of approximately 0.06 grams per cubic centimeter. These extremely low densities suggest that these planets have a substantial proportion of their mass composed of lighter elements, such as hydrogen and helium, and possess very large radii relative to their mass.

Researchers utilized data from NASA's Transiting Exoplanet Survey Satellite (TESS) and the James Webb Space Telescope (JWST) to analyze the atmospheric composition and physical characteristics of these exoplanets. The JWST's advanced spectroscopic capabilities allowed for a detailed examination of the light passing through the planets' atmospheres, revealing the presence of water vapor and methane. This analysis helped scientists infer the overall composition and structure of the planets.

The discovery of such low-density planets challenges current models of planet formation and evolution. Scientists are investigating how these 'super-puff' planets form and maintain their expansive atmospheres. The extreme conditions under which these planets exist, including their proximity to their host star and the composition of their stellar nebula, are being studied to understand the diversity of planetary systems in the galaxy. Further observations are planned to refine the mass and radius measurements and to search for similar low-density exoplanets.