Planets so light they would float, yet as large as Jupiter
Somewhere in the vast catalog of distant suns, two worlds the size of Jupiter drift in orbits so improbable that they have forced astronomers to pause and reconsider the rules they thought governed planetary creation. Discovered by NASA's TESS space telescope, these 'super-puff' planets are Jupiter-sized in girth yet so extraordinarily light — their densities likened to shaving foam or cotton candy — that they represent the least massive gas giants ever detected. Their existence is not merely a curiosity; it is a quiet challenge to the foundational models of how giant planets are born, suggesting that the universe harbors categories of worlds our theories have not yet learned to imagine.
- Two Jupiter-sized planets have been found with densities so impossibly low they would float in water, defying every expectation built into modern planetary science.
- The discovery creates immediate tension with accepted formation models, which cannot easily explain how a world can grow so large while accumulating so little mass.
- Finding not one but two such objects transforms a potential anomaly into a possible population, raising the unsettling possibility that super-puff planets are common and simply overlooked.
- Astronomers are now weighing competing explanations — unusual formation pathways, planetary migration that stripped away material, or early solar system conditions unlike anything previously modeled.
- NASA's TESS mission, designed to watch rather than seek, continues to surface the unexpected, and its ongoing sky survey promises further discoveries that may deepen rather than resolve the mystery.
Two planets the size of Jupiter have been discovered orbiting distant stars, and they are so extraordinarily light that they would float in water. Found by NASA's TESS space telescope, these worlds — nicknamed 'super-puff' planets — possess densities that researchers struggle to describe without reaching for unusual comparisons: shaving foam, cotton candy. The analogies are not whimsical. They point to something genuinely strange: enormous spheres of gas held together by gravity, yet weighing almost nothing by planetary standards. They are the lightest gas giants ever detected.
TESS identified the pair by measuring the faint dimming of starlight as each planet passed in front of its host star. Combining that size data with mass estimates revealed the startling truth — Jupiter's bulk, but a fraction of Jupiter's weight. The numbers did not fit the existing framework for how gas giants form, in which a rocky core gathers hydrogen and helium until a massive world takes shape. These planets are too large and too light to sit comfortably within that story.
What elevates the discovery beyond curiosity is the count: two. A single anomalous world might be set aside as an outlier. Two suggests a class of object — and if super-puff planets are genuinely common, then the universe contains a category of world that current theory cannot yet explain. Astronomers are now asking whether these planets formed through different mechanisms, migrated in ways that shed material, or emerged from early solar system conditions unlike anything previously assumed.
The gap between what TESS observes and what models predict is precisely where new science tends to grow. The mission was never designed to find any particular kind of planet — it simply watches thousands of stars and records what happens. In doing so, it has revealed that the universe remains more inventive than the frameworks built to describe it.
Two planets the size of Jupiter have just been discovered orbiting distant stars, and they are so impossibly light that they would float in water. Astronomers using NASA's TESS space telescope found these worlds, which they call "super-puff" planets, and the discovery is forcing a reckoning with everything scientists thought they understood about how giant planets form.
The two worlds are Jupiter-sized in diameter but possess a density so low that researchers struggle to find earthly comparisons. One astronomer described them as comparable to a blob of shaving foam. Another reached for cotton candy. The analogy matters because it conveys something real: these are not dense, rocky bodies or even typical gas giants. They are, in essence, enormous clouds held together by gravity—and they are the lightest gas giants ever detected.
The TESS mission, which has been systematically scanning the sky for exoplanets since its launch, identified these two worlds. TESS works by measuring the tiny dip in starlight that occurs when a planet passes in front of its host star, allowing astronomers to infer the planet's size. Combined with other observational techniques, scientists can estimate mass and therefore density. What emerged from the data was startling: planets with the bulk of Jupiter but a fraction of its weight.
This discovery matters because planetary formation theory has long struggled to explain how such objects could exist. Current models suggest that gas giants form through a specific sequence of events—a rocky core accumulates, gravity pulls in hydrogen and helium, and a massive world takes shape. But these super-puff planets seem to violate the expectations baked into those models. They are too large and too light to fit neatly into the existing framework.
The implications ripple outward. If these worlds are real—and the TESS data strongly suggests they are—then astronomers must consider new formation mechanisms. Perhaps these planets formed differently than Jupiter and Saturn. Perhaps they migrated through their solar systems in ways that stripped away material. Perhaps the early solar system operated under different rules than scientists have assumed. The questions multiply faster than the answers.
What makes the discovery particularly significant is that TESS has now found not one but two such objects. A single anomaly might be dismissed as an outlier. Two suggests a population. If super-puff planets are common, then the universe contains a category of world that current theory cannot easily accommodate. That gap between observation and explanation is where new science lives.
The discovery also underscores the power of systematic sky surveys. TESS is not hunting for any particular type of planet. It is simply watching thousands of stars and recording what it sees. In doing so, it has revealed worlds that challenge assumptions and expand the inventory of planetary possibilities. As the mission continues, more surprises likely await. The universe, it seems, is more creative than the models that attempt to describe it.
Notable Quotes
Comparable to a nice blob of shaving foam— Astronomer describing the planets' density
The Hearth Conversation Another angle on the story
When you say these planets are lighter than cotton candy, what does that actually mean in physical terms?
It means if you could somehow place one on a scale, it would weigh far less than a Jupiter-sized object made of normal matter should. The density is so low that the material is mostly empty space—held together by gravity but barely.
How do astronomers even measure something like that from billions of miles away?
They watch the star the planet orbits. When the planet passes in front of it, the starlight dims slightly. That tells you the planet's size. Then other techniques—like measuring the gravitational tug on the star—reveal the mass. Size divided by mass gives you density.
And these two planets broke the density record?
Completely. They are the lightest gas giants we have ever found. That alone would be interesting. But what's unsettling is that our theories about how planets form don't predict objects like this should exist.
What does that mean for what we think we know?
It means we have to go back and ask harder questions. Maybe planets form in ways we haven't considered. Maybe they change after formation in ways we don't understand. The discovery doesn't answer those questions—it just makes them impossible to ignore.
Will finding more of them change how urgent those questions feel?
Absolutely. One anomaly is a curiosity. Two suggests a pattern. If TESS finds dozens of super-puff planets, it becomes clear that this is not an edge case—it's a fundamental feature of planetary systems that theory needs to explain.