Picture a planet as wide as Jupiter that weighs almost nothing — a world you could, in principle, scoop up like a handful of foam. Astronomers say they have found two of them, circling a Sun-like star roughly 1,113 light-years from Earth, and together they are the lightest planets of their size ever recorded.
The pair, designated TOI-791 b and TOI-791 c, belong to a scarce and stubbornly puzzling class of worlds nicknamed “super-puffs”: gas giants so bloated and so sparse that their density rivals candy floss. A team led by the University of Oxford reported the discovery on Wednesday, 24 June 2026, in Monthly Notices of the Royal Astronomical Society, with NASA detailing the find the same day.
How light is light? TOI-791 b is nearly the same size as Jupiter but holds just 3.0 percent of its mass. Its sibling, TOI-791 c, is even larger than Jupiter yet carries only 5.9 percent of the giant’s heft. Jupiter, by comparison, is as much as 35 times denser than either of them.
“These two planets have densities comparable to a nice blob of shaving foam, fresh from the can.”
George Dransfield, University of Oxford, lead author
Dransfield, who described the pair in an email to The Associated Press, suspects the worlds are white or blue rather than the candy-pink the nickname implies — their true color hinges on whether their skies are cloudy. Both are thought to be mostly hydrogen and helium, though pinning down that chemistry will take follow-up observations from NASA’s James Webb Space Telescope.
| Planet | Size | Mass (vs. Jupiter) | Orbit |
|---|---|---|---|
| TOI-791 b | Nearly Jupiter-sized | 3.0% | 139 days |
| TOI-791 c | Larger than Jupiter | 5.9% | 232 days |
Finding one super-puff is unusual. Finding two around the same star is rarer still. NASA’s running tally of worlds beyond our solar system now stands at nearly 6,300 confirmed planets; fewer than 40 of them qualify as super-puffs, according to Dransfield. The TOI-791 system, sitting in the southern constellation Volans — the flying fish — just doubled the odds in a single stroke.
Getting there took patience. NASA’s Transiting Exoplanet Survey Satellite, or TESS, spotted the planets by watching for tiny, repeated dips in the star’s brightness, the telltale flicker of a world crossing in front of it. Over seven years the spacecraft gathered 1,122 days of data on this one system. That long baseline mattered, because both planets travel unusually wide, slow orbits, and short surveys simply miss them.
The two worlds also gave themselves away by leaning on each other. As they swing around their star, TOI-791 b and TOI-791 c tug gravitationally back and forth, nudging the timing of each other’s transits by small but measurable amounts. Researchers used those variations to weigh the planets — and the answer, improbably small, cemented their status as featherweights.
“The main reason these planets are interesting to study is that we didn’t expect to see them at all. They represent a puzzle for us to solve about how giant planets like Jupiter and the super-puffs form.”
Jon Jenkins, NASA Ames Research Center
That puzzle is the real prize here. Conventional models say a planet this wide should be far heavier. Super-puffs are thought to take shape in the gas-rich outer reaches of a young star’s disk, where there is more gas than dust, then shed much of their bulk over time. But the details — how a world ends up Jupiter-wide and shaving-foam-light — remain genuinely unsettled, which is exactly why a clean two-planet laboratory like TOI-791 is so useful.
The find lands amid a busy stretch for exoplanet science. Webb has been picking apart the atmospheres of far stranger worlds, from the scorching dawn-to-dusk extremes of WASP-121 b to the kind of refined models now narrowing the search for life. Against that backdrop, two planets you could practically blow away are a reminder of how much the catalogue of nearby worlds still defies expectations.
For now, TOI-791 b and TOI-791 c stay on the list of targets astronomers most want Webb to revisit. Whatever the telescope finds in their thin, hydrogen-rich air, the planets have already done the one thing scientists value most from a discovery 1,100 light-years away: they refuse to behave.
