NASA Just Found Planets As Light As Cotton Candy — and They're the Size of Jupiter

Two 'super-puff' exoplanets, TOI-791 b and TOI-791 c, are among the lowest-density worlds ever discovered — giant planets so diffuse they'd float on water, if you could find a bathtub big enough.

Call them the universe's most improbable balloons.

NASA's TESS mission has confirmed two extraordinary new exoplanets — TOI-791 b and TOI-791 c — that are roughly the diameter of Jupiter yet so staggeringly diffuse that their density clocks in below that of cotton candy. TOI-791 b has a density of just 0.038 grams per cubic centimetre. For comparison, cotton candy is around 0.05 g/cm³. These are, quite literally, lighter than carnival sweets.

The two worlds orbit a star 1,113 light-years from Earth, and belong to an extremely rare class of planets astronomers call "super-puffs" — gas giants whose atmospheres have ballooned to improbable sizes while their masses remain unexpectedly low. How such planets form and survive, especially so close to their host star, is a puzzle that's forcing a rethink of planetary evolution models.

The discovery, led by researchers at the University of Oxford and the University of Birmingham, was published in late June 2026 and quickly picked up by NASA as one of TESS's most visually arresting finds since the mission began. "These are the puffiest planets we've ever confirmed," the NASA team noted — worlds where a human would sink through the atmosphere as if it weren't there, finding no surface, only an ever-thickening haze of hydrogen and helium.

It's a reminder that the cosmos still has a sense of whimsy. Jupiter-sized planets with the consistency of spun sugar, floating in the dark, waiting to be explained.

Sources: NASA, ScienceDaily, University of Oxford