A planet this large should contain far more mass. The fact that it does not suggests something unexpected.
Somewhere beyond our solar system, two worlds drift through space so vast and so light that they challenge the very grammar of what a planet is supposed to be. Astronomers using NASA's TESS space telescope have identified the largest and least dense super-puff exoplanets ever recorded — gas giants whose density rivals that of cotton candy — pushing the boundaries of planetary science and inviting a deeper reckoning with how worlds are born and shaped. These discoveries remind us that the universe remains far more inventive than our models, and that each new world found is also a question posed to everything we thought we understood.
- Two exoplanets have shattered records for low density, so light and enormous that they defy conventional expectations for gas giants of their size.
- Their existence creates a genuine scientific tension: a planet this large should contain far more mass, and the fact that it does not demands an explanation current models struggle to provide.
- Competing theories — from close-in formation followed by outward migration, to runaway atmospheric inflation, to catastrophic atmospheric loss — are now being weighed against these extreme new data points.
- NASA's TESS telescope, still mid-mission with years of data ahead, continues to surface planetary configurations that force astronomers to revise their foundational assumptions about how planets form and evolve.
Two planets are drifting through the cosmos so light and expansive that the comparison to cotton candy is less poetic flourish than precise description. Astronomers working with NASA's TESS space telescope have announced the discovery of the largest and least dense super-puff exoplanets ever found — worlds so enormous in diameter yet so slight in mass that they would, in theory, float in water.
Super-puff planets are gas giants composed primarily of hydrogen and helium, but what sets them apart is not their ingredients — it is how little of those ingredients they actually contain. Where a typical gas giant follows predictable patterns of size and mass, super-puffs break the relationship entirely, presenting vast diameters alongside densities that seem almost impossible.
TESS detects planets by watching for the faint dimming of starlight as a world passes in front of its host star. By combining this transit data with additional observations, astronomers can estimate a planet's size, mass, and density. These two new worlds represent the most extreme examples the method has yet uncovered.
The leading explanations involve planets that formed near their stars and migrated outward, worlds that accumulated unusually thick atmospheres while remaining low in mass, or planets that shed much of their original atmosphere over time. Each theory carries different implications for how planetary systems evolve.
For the broader field, the discovery underscores how varied the universe's planetary output truly is. With years of TESS observations still being analyzed, the catalog of known exoplanets continues to grow stranger and richer — each new transit, each dip in distant starlight, a potential revision to everything astronomers thought they knew.
Somewhere in the cosmos, two planets are floating through space so light and airy that if you could somehow hold them in your hand, they would feel less substantial than spun sugar. Astronomers working with NASA's TESS space telescope have just announced the discovery of these two record-breaking worlds—the largest and least dense super-puff planets ever found. Their density is so remarkably low that the comparison to cotton candy is not metaphorical; it is the most accurate way to convey just how little mass these gas giants actually contain.
Super-puff planets represent one of the great puzzles in planetary science. They are gas giants, meaning they are composed primarily of hydrogen and helium, the lightest elements in the universe. But what makes them extraordinary is not what they are made of—it is how little of it they have. A typical gas giant might be expected to have a certain mass relative to its size, following patterns astronomers have observed in our own solar system and in thousands of exoplanets catalogued over the past few decades. Super-puffs defy this expectation. They are enormous in diameter yet possess remarkably little mass, creating a density so low that they would float in water if such a thing were possible.
The TESS mission, which stands for Transiting Exoplanet Survey Satellite, has been systematically scanning the sky since its launch, watching for the telltale dimming of starlight that occurs when a planet passes in front of its host star. This method, called the transit technique, allows astronomers to infer a planet's size and, when combined with other observations, to estimate its mass and therefore its density. TESS has proven remarkably effective at finding unusual worlds, and these two super-puffs represent some of the most extreme examples yet discovered.
What makes this discovery significant is not merely that these planets exist—astronomers have known about super-puffs for years—but that these two are the largest and lightest of their kind. They push the boundaries of what planetary scientists thought possible. A planet this large should, by conventional understanding, contain far more mass. The fact that it does not suggests something unexpected about how these worlds formed or how they evolved after formation.
The leading theories about super-puff formation involve either a planet that formed very close to its star and then migrated outward, or a world that somehow managed to accumulate an unusually thick and puffy atmosphere while remaining relatively low in overall mass. Another possibility is that these planets lost significant amounts of their original atmosphere over time, leaving behind a bloated remnant. Each scenario tells a different story about planetary history and the forces that shape worlds.
For astronomers, the discovery opens new questions about planetary diversity. The universe appears to produce planets in far more varied configurations than models predicted even a decade ago. Super-puffs challenge the assumption that size and mass should correlate in predictable ways. Understanding why these planets are so different from what theory suggested may require rethinking fundamental ideas about how planets accumulate material and how their atmospheres behave.
The TESS mission continues to deliver surprises. With years of observations still being analyzed and years more of data collection ahead, the space telescope is systematically expanding the catalog of known exoplanets and revealing the full range of planetary possibilities. Each discovery, including these two remarkable super-puffs, adds another data point to the growing picture of how planets form, evolve, and persist across the galaxy. The next breakthrough may come from the next transit, the next dip in starlight, the next world waiting to be found.
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When you say these planets are lighter than cotton candy, are you speaking literally or is that just a comparison for scale?
It's literal in the sense that if you measured the density—mass per unit volume—it would be lower than actual cotton candy. Of course, you can't put a planet on a scale, but the physics checks out. The density is that remarkably low.
How do astronomers even measure the mass of something so far away?
They use the gravitational pull the planet exerts on its star. When a planet orbits, it tugs on the star slightly, causing the star to wobble. By measuring that wobble, or by observing how the planet's gravity affects the timing of its transits, astronomers can calculate mass. Combined with the size—which comes from watching how much starlight the planet blocks—you get density.
So TESS is just watching stars get dimmer?
Essentially, yes. But it's watching millions of stars continuously, looking for that specific pattern of dimming that indicates a planet passing in front. It's patient, systematic work. And when you observe enough stars, you find the unusual ones.
Why would a planet be so puffy if it's not that massive?
That's the real question. It could have formed differently than we thought, or migrated in ways that changed its structure. It might have a massive atmosphere that somehow stayed attached despite the low gravity. Or it could be a remnant—a planet that was once heavier but lost its outer layers over billions of years.
Does finding these change how we think planets form?
It has to. When your models predict planets should look one way and you keep finding planets that look completely different, you have to ask what you're missing. These super-puffs are telling us that planetary formation is messier, more varied, more creative than we assumed.
What comes next for these discoveries?
More observation. Astronomers will study these planets in detail, try to understand their atmospheres, their temperatures, their orbital characteristics. And TESS will keep finding more. Each one adds texture to the picture.