The James Webb Space Telescope has caught a rare kind of exoplanet in the act of falling apart, revealing a world so light and distended that astronomers compare it to a ball of cotton candy. The planet, WASP-107b, is shedding a vast plume of gas that trails behind it like a comet tail, a sign that its fragile atmosphere is being stripped away as it orbits close to its star. In tracking this “super-puff” as it effectively chases its own escaping air, researchers are getting a sharper look at how extreme worlds form, migrate and eventually die.
A cotton-candy world with the density of a puff
Super-puff exoplanets sit in one of the strangest corners of planetary science, with sizes comparable to Jupiter but masses closer to Neptune, which leaves them with densities that are more like foam than rock or gas. WASP-107b fits that bill, a swollen giant whose bulk is dominated by a bloated atmosphere rather than a hefty core, which is why astronomers reach for metaphors like cotton candy to describe it. When I look at the broader family of these worlds, I see a class of planets that stretches the usual categories of “rocky,” “icy” and “gas giant” to the breaking point, forcing modelers to rethink how much atmosphere a small core can realistically hold.
Earlier work on other low-density systems, such as the Kepler‑51 planets, already showed that some exoplanets can be so puffy that their atmospheres extend to extraordinary heights, a fact that was vividly illustrated in an Image via NASA and ESA that compared them to cosmic cotton candy. WASP-107b now joins that select group, but with a twist: instead of simply being large and light, it is actively losing its outer layers in a way that Webb can watch in real time. That combination of extreme puffiness and visible escape makes it a kind of laboratory for testing how fragile atmospheres behave under intense stellar radiation.
WASP-107b’s helium plume and the chase for its own air
The most striking feature of WASP-107b is the enormous plume of helium that is streaming away from the planet, a signature that the atmosphere is not just extended but actively evaporating into space. Observations with the James Webb Space Telescope revealed that this helium is not confined to a thin shell but forms a broad tail that wraps around the planet’s orbit, so that the world effectively moves through a cloud of its own lost gas. When I think about that geometry, I picture a runner circling a track while moving through a fog that they themselves are exhaling, a vivid way to understand why astronomers describe the planet as chasing its own atmosphere.
That helium plume was first highlighted in detailed reporting on how the James Webb telescope tracked gas evaporating from the giant planet known as WASP-107b. The same work emphasized that the plume is not a subtle effect but a large-scale structure that dominates the space around the planet, a sign that the escape process is vigorous rather than gentle. For atmospheric scientists, that scale matters, because it suggests that the upper layers are heated and accelerated enough to overcome the planet’s weak gravity, turning WASP-107b into a textbook example of hydrodynamic escape in action.
Why helium escape on this planet is a first
Helium loss has been seen on other exoplanets before, but WASP-107b stands out because it is the first time astronomers have watched such escape on a world with this kind of ultra-low density. In previous cases, the planets tended to be more compact hot Jupiters, where the gas is tightly bound and the escaping helium traces a relatively thin outflow. Here, the same process is playing out in a much looser gravitational environment, so the gas can spread into a vast, diffuse envelope that is easier to detect and map. That difference turns WASP-107b into a bridge between the better known hot Jupiters and the more mysterious super-puffs, linking two previously separate lines of research.
Coverage of the new results underscored that, While helium escape has been observed on other exoplanets, WASP-107b marks the first time astronomers have watched an exoplanet in the “super-puff” category lose its atmosphere in this way. That distinction is not just a matter of classification, it means that the same physical mechanism can operate across a wider range of planetary sizes and densities than models once assumed. In my view, that pushes theorists to revisit how quickly such planets can erode, and whether some of the smaller, denser worlds we see today might be the stripped cores of former super-puffs that went through a similar phase of intense helium loss.
What Webb’s spectrum reveals about the planet’s chemistry
Beyond the helium plume, the James Webb Space Telescope has given researchers a detailed spectrum of WASP-107b’s atmosphere, revealing a mix of elements and molecules that help reconstruct the planet’s history. By splitting the starlight that filters through the atmosphere into its component colors, Webb can pick out the fingerprints of different gases, from light species like helium to heavier compounds that trace deeper layers. When I look at those spectra, I see more than a list of ingredients, I see a timeline of how the planet formed, migrated and is now being reshaped by its star’s radiation.
Reporting on the Webb observations noted that the researchers spotted several elements in the atmosphere and that the pattern of those detections suggests the planet’s migration was relatively recent, a conclusion that rests on how the chemistry has not yet been fully reworked by long-term heating. The same analysis pointed out that JWST also found water in the atmosphere, a key marker that helps constrain the planet’s temperature and vertical structure. For me, the presence of water vapor alongside escaping helium paints a picture of a layered atmosphere where deeper, cooler regions still hold complex molecules even as the upper layers are being stripped away, a dynamic balance that only a sensitive instrument like Webb can untangle.
How a “black widow” style star drives atmospheric escape
WASP-107b orbits very close to its host star, which bathes the planet in intense radiation and stellar wind that act like a blowtorch on its upper atmosphere. In such a tight orbit, the planet’s outer layers are heated until they expand and eventually reach escape velocity, allowing gas to stream away and form the observed plume. I see this configuration as a milder cousin of the so-called “black widow” systems, where a compact star strips material from a companion, because the underlying physics is similar: a powerful central object gradually erodes a nearby partner through relentless energy input.
Accounts of the Webb discovery described the planet as having an atmosphere orbiting a “black widow” star, a vivid phrase that captures how the star’s radiation is effectively consuming the planet’s gaseous envelope. That comparison matters because it highlights the long-term stakes: if the current rate of escape continues, WASP-107b could lose a significant fraction of its atmosphere over its lifetime, potentially transforming from a super-puff into a smaller, denser remnant. From my perspective, that evolution turns the system into a natural experiment in planetary survival, showing how close-in worlds can be sculpted or even destroyed by the very stars that made them possible.
Super-puffs, Kepler-51 and the broader family of fluffy planets
WASP-107b does not exist in isolation, it is part of a growing catalog of super-puff planets that challenge standard formation theories. Systems like Kepler‑51, where multiple low-density planets orbit the same star, already forced astronomers to confront the idea that some worlds can retain enormous atmospheres despite relatively small cores. When I compare WASP-107b to those earlier examples, I see a continuum of puffiness, from moderately inflated Neptunes to extreme cotton-candy giants, all of which sit in a regime where small changes in temperature or stellar activity can have outsized effects on atmospheric loss.
The Kepler‑51 discoveries were famously illustrated in an ESA graphic that compared the planets’ sizes to Jupiter while emphasizing their much lower masses, a visual that helped cement the “cotton candy” nickname. WASP-107b extends that story by adding direct evidence of atmospheric escape, something that was harder to pin down in the more distant Kepler systems. In my view, that combination of puffiness and active loss suggests that super-puffs might be inherently transient, spending only a fraction of their lifetimes in this inflated state before shrinking as their atmospheres bleed away.
Clues to migration and the planet’s past
One of the key questions about WASP-107b is how it ended up so close to its star while still retaining such a large, fragile atmosphere. If the planet formed far from the star and migrated inward later, it might have had more time to build up a thick envelope before the intense radiation began to strip it away. The chemical fingerprints that Webb sees, including the mix of helium, water and heavier elements, offer hints about where the planet originally accreted its gas and how quickly it moved to its current orbit.
Analyses of the Webb data have argued that the combination of detected elements suggests the planet’s migration was relatively recent, because a longer stay in the current hot environment would likely have altered the atmospheric composition more dramatically. The fact that the researchers spotted several elements that point to a relatively pristine envelope supports the idea that WASP-107b has not been parked in its current orbit for billions of years. To me, that scenario is compelling because it ties the planet’s present-day puffiness and atmospheric loss to a dynamic past, where gravitational interactions or disk forces nudged it inward only after it had already grown into a low-density giant.
What this means for the future of WASP-107b
Looking ahead, the fate of WASP-107b depends on how long it can keep feeding its escaping plume from the deeper layers of its atmosphere. If the current rate of loss is sustained, the planet could gradually shed a large fraction of its gas, eventually exposing a smaller, denser core that would look very different from the cotton-candy world Webb sees today. I find that prospect intriguing because it suggests that some of the compact, rocky or Neptune-like planets we observe around other stars might be the end states of once-puffy giants that went through a similar phase of intense erosion.
Reports on the system have already framed WASP-107b as a kind of preview of that long-term evolution, emphasizing that a “super-puff” exoplanet is losing its atmosphere to its star. For planetary scientists, that framing is powerful because it connects a snapshot in time to a broader life cycle, from formation in a gas-rich disk to migration, inflation and eventual stripping. As Webb and other observatories continue to monitor WASP-107b, I expect the planet to become a benchmark for testing models of atmospheric escape, helping to explain not only its own strange state but also the diversity of exoplanets that populate the galaxy.
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