Astronomers Discover Pair of Jupiter-Sized 'Super-Puff' Exoplanets Lighter Than Cotton Candy

The universe has a remarkable knack for producing celestial objects that completely defy human intuition, but few discoveries are as perplexing as the newly confirmed exoplanets orbiting the distant star TOI-5803. Located approximately 1,200 light-years from Earth in the constellation of Cygnus, this seemingly ordinary star system has just unveiled two gas giants that are fundamentally rewriting the rules of planetary physics. These worlds are not just slightly unusual; they represent an extreme outlier in planetary formation that challenges the very foundation of how we believe gas giants are born and evolve over billions of years.[1][6]

Using an unprecedented combination of data from the James Webb Space Telescope (JWST) and NASA's Transiting Exoplanet Survey Satellite (TESS), an international team of astronomers has confirmed that TOI-5803 b and c belong to an ultra-rare category known as "super-puffs." These are a bizarre class of planets characterized by massive, bloated volumes but astonishingly little mass. While astronomers have found a handful of these low-density worlds over the past decade, the newly discovered pair pushes the physical limits of this category further than anything previously observed, offering a pristine laboratory for studying extreme atmospheric physics.[2][4]

To understand just how bizarre these alien worlds truly are, one must look closely at their overall density. Jupiter, the largest and most massive planet in our own solar system, is a dense ball of gas and liquid metallic hydrogen with a density of about 1.33 grams per cubic centimeter. In stark contrast, the two newly discovered planets boast an almost incomprehensible density of just 0.04 grams per cubic centimeter. This makes them less dense than a standard puff of spun sugar, fundamentally altering our understanding of how matter can aggregate in the vacuum of space.[1][5]

In highly practical, terrestrial terms, this density measurement makes them slightly less dense than actual cotton candy. If you could theoretically construct a bathtub large enough to hold them, and fill it with water, both TOI-5803 b and c would easily float on the surface like massive, cosmic beach balls. This extreme lack of density means that an astronaut attempting to descend into the planet's atmosphere would experience a near-endless freefall through thousands of miles of increasingly thick, but still incredibly wispy, hydrogen and helium gas, never encountering a solid surface or even a dense liquid core.[4][6]

The timeline of this groundbreaking discovery began in early 2026, when the TESS satellite, which constantly monitors the sky for the telltale signs of transiting planets, detected significant, recurring dips in the starlight coming from the TOI-5803 system. The sheer amount of light being blocked during these transits suggested the presence of two massive planets, both roughly 1.5 times the physical size of Jupiter. However, the transit method only reveals a planet's physical radius; it tells astronomers absolutely nothing about how much matter is actually packed inside that massive silhouette.[2][5]

Because size is only half the planetary equation, astronomers desperately needed to measure the mass of these new worlds to understand their true nature. To accomplish this, they turned to highly sensitive ground-based observatories equipped with advanced spectrometers. These instruments measure the star's radial velocity—the microscopic, rhythmic "wobble" induced by the gravitational pull of the orbiting planets as they circle their host star. By measuring exactly how much the star was being tugged back and forth, the research team could calculate the precise gravitational mass of the unseen planets pulling on it.[1][3]

The results from the radial velocity measurements were nothing short of shocking to the astronomical community. Despite their immense, Jupiter-dwarfing size, the planets exerted barely any gravitational pull on their host star. The complex calculations revealed that they contain only about one-seventh the total mass of Jupiter. This means that their vast, imposing bulk is almost entirely composed of a highly inflated, wispy atmosphere that stretches incredibly far out into space, tethered to a surprisingly tiny and lightweight planetary core.[3][5]

This extreme "fluffiness" presents a massive, immediate headache for theoretical astrophysicists who study planetary origins. The standard, widely accepted framework for how gas giants form, known as the core accretion model, struggles mightily to explain how a planet could hold onto such a massive, diffuse envelope of gas without it rapidly dissipating into the vacuum of space. Under normal circumstances, a planet requires a massive gravitational anchor to keep light gases like hydrogen and helium from boiling away under the intense radiation of its host star.[1][6]

According to traditional core accretion models, a developing planet needs a substantial rocky or icy core—usually about ten times the mass of Earth—to generate enough gravity to pull in and hold onto a thick atmosphere. If the core is too small, the surrounding gas simply escapes into the protoplanetary disk; if the core is large enough, the immense gravity compresses the gathered gas into a dense, compact sphere like Jupiter or Saturn. There is virtually no mechanism in the standard textbook that allows for a planet to be this large and this light simultaneously.[3][4]

TOI-5803 b and c sit squarely in an impossible middle ground that defies these established rules. Their internal gravity should not be nearly strong enough to maintain their bloated size, especially given their relatively close proximity to their host star, which bombards them with intense heat and stellar radiation. This radiation should, theoretically, be stripping their delicate atmospheres away at a catastrophic rate, leaving behind nothing but barren, rocky cores. The fact that they exist in this bloated state today implies that a hidden mechanism is actively working to keep them inflated.[1][5]

Researchers have proposed a few competing hypotheses to explain the anomaly, though none are entirely perfect. One leading theory suggests that the planets are experiencing intense, continuous internal heating. This could be driven by tidal forces—complex gravitational tugs-of-war between the two massive planets and their host star. This constant squeezing and stretching of the planets' interiors could generate immense friction deep within their cores, radiating heat outward and causing their atmospheres to puff up dramatically, much like a hot air balloon expanding as the air inside is heated.[3][6]

Another strong possibility is that our telescopes are being deceived, and we are not actually seeing the true size of the planets' atmospheres. Some scientists argue that high-altitude photochemical hazes—similar to the thick, opaque smog that completely blankets Saturn's moon Titan—could be tricking our instruments. These dense hazes might be suspended high above the actual, much smaller atmosphere, blocking the starlight during a transit and making the planets appear significantly larger, and therefore much less dense, than they truly are beneath the smog.[1][4]

A third, more radical theory suggests that these planets are currently in the active process of dying, and we are simply catching them at a unique moment in time. Because their gravity is so weak, the intense stellar winds from the TOI-5803 star might be actively and violently stripping their atmospheres away into space. In this scenario, the planets are "bleeding" gas, creating a massive, temporary cloud around them. We are simply observing them during a fleeting, transitional phase before they are ultimately reduced to small, dense, and barren rocky cores over the next few hundred million years.[3][5]

To definitively solve this cosmic mystery, astronomers have already secured highly coveted additional observation time on the James Webb Space Telescope. By utilizing the telescope's incredibly powerful infrared spectrographs, they hope to peer directly through the outer layers of the planets' atmospheres. This next phase of research will allow them to determine the exact chemical composition of the gases, measure the rate of atmospheric escape, and definitively detect or rule out the presence of any high-altitude hazes that might be skewing the size measurements.[1][4]

Regardless of the final, definitive explanation, the discovery of TOI-5803 b and c serves as a humbling and exhilarating reminder of the cosmos's boundless creativity. As our astronomical instruments grow increasingly sophisticated, we are continually finding that the universe is not just stranger than we previously imagined, but often stranger than our current mathematical models even allow. These cotton-candy worlds prove that the galaxy is filled with endless variations, pushing scientists to constantly revise, adapt, and expand their understanding of how planetary systems are born.[5][6]