Imagine a planet the size of Jupiter—a gas giant so massive it dwarfs Earth a thousand times over—and then imagine it weighing less than a cloud of spun sugar. That’s not science fiction. That’s what astronomers just discovered orbiting a distant star, and it’s forcing researchers to rethink how planets actually form.
Two so-called“super-puff”planets, named TOI-791b and TOI-791c, were spotted some 1,110 light years away in the southern constellation of Volans. The kicker? Their densities are 28 to 35 times lower than Jupiter’s. TOI-791b clocks in at just 0.038 grams per cubic centimeter, and TOI-791c at 0.047—both lighter than cotton candy, which typically registers around 0.05 grams per cubic centimeter. To put that in perspective, Earth packs a density of 5.5 grams per cubic centimeter. These planets are, in every measurable sense, extraordinarily diffuse.
What makes this discovery even rarer is that researchers found not one but two of these fluffy giants in the same system, locked together in a gravitational dance known as a 5:3 mean-motion resonance. For every five orbits the inner planet completes, the outer one finishes almost exactly three. That relationship creates a celestial choreography: the planets tug on each other in ways measurable enough to shift the timing of their transits across their host star. The lead research team—led by Dr. George Dransfield from Oxford and collaborators from the University of Birmingham and Université Côte d’Azur in France—identified these patterns by analyzing data gathered from citizen-science volunteers participating in the Planet Hunters TESS project, then confirmed the discovery using telescopes scattered across continents and, critically, Antarctica.
The Antarctic advantage deserves its own spotlight. The months of continuous Antarctic winter darkness allowed astronomers to capture the planets’exceptionally long transits—each lasting more than 11 hours—in a single uninterrupted observation. Those marathon transit events provided the detailed measurements needed to estimate the planets’masses and calculate their jaw-dropping densities. It’s a reminder that sometimes the most cutting-edge astronomy happens not in high-tech laboratories but in humanity’s most extreme environments.
So why does this matter? Astronomers are still debating how super-puff planets form in the first place. Their extreme diffuseness remains one of the great open questions in exoplanet science. The research team plans to use the James Webb Space Telescope to analyze the composition of these planets’atmospheres, searching for carbon-, nitrogen-, and oxygen-bearing species that might reveal clues about their origins. Every puzzle piece brings us closer to understanding the mechanics of planetary birth itself.
The discovery of TOI-791b and TOI-791c reminds us that the universe isn’t just vast—it’s weird in ways we’re still learning to appreciate.
About the Author
Andrew Johnson
Andrew Johnson is a contributor to LocalBeat, covering local news and community stories.
