James Webb Space Telescope (JWST) has made a discovery that stretches the limits of what we thought possible in planetary atmospheres. Around a “black widow” pulsar known as PSR J2322-2650, they’ve found a planet — PSR J2322-2650b — whose atmosphere appears to be composed almost entirely of carbon. This is not just unusual, it’s almost alien by Earth’s standards. The finding challenges existing models of how such systems evolve and suggests we have much yet to learn about planet formation under extreme conditions.
What Is a “Black Widow” System?
To understand this discovery, it helps to know what a black widow pulsar is. A black widow is a type of millisecond pulsar (a rapidly spinning neutron star) that “eats” or strips material off a companion star. Over time, intense radiation and strong winds from the pulsar gradually erode and consume its partner. In many cases, what remains is a small, swollen, heated object—sometimes a kind of giant planet or “hot Jupiter”-like body—after the star loses its outer layers.
PSR J2322-2650 is one such system. The companion in this case, PSR J2322-2650b, orbits very closely (about every 7.8 hours), and previous observations suggested it had characteristics similar to helium-dominated planets that have been stripped to almost nothing. But what JWST has seen goes far beyond a helium atmosphere.
An Atmosphere Made of Carbon—Really
The headline is that this planet’s atmosphere appears to be nearly pure carbon. The spectroscopic data from JWST suggest the presence of molecules like C₂ (dicarbon) and C₃ (tricarbon) dominate. That means molecules typically associated with soot, flames, or comet tails on Earth are playing the starring role here.
To put this in perspective: the measured carbon-to-oxygen (C/O) ratio is over 100, and the carbon-to-nitrogen (C/N) ratio is over 10,000. On Earth, the C/O ratio is roughly 0.01, and C/N about 40. So we’re looking at a totally different chemical environment.
Day vs Night: Scorching Heat and Sooty Darkness
Because PSR J2322-2650b is likely tidally locked (meaning one face always points toward the pulsar, the other always faces away), the day side and night side are vastly different based on JWST reference. The side facing the pulsar can reach temperatures exceeding 2,000 °C, hot enough to generate clear, strong spectral signatures. The night side shows almost nothing—very few features in the spectrum. Scientists suggest that side may be blanketed in soot-like material, which masks any signatures.
Another interesting dynamic seen in the data concerns atmospheric circulation. The hottest point on the planet isn’t directly facing the pulsar; it’s shifted westward by about 12 degrees. This suggests strong westerly winds are transporting heat around, something that models of rapidly rotating planets around pulsars or hot stars had predicted, but this is among the first observational evidence of it.
Why This Discovery Defies Expectations
Given what is expected of black widow systems, this planet shouldn’t have had a carbon-rich atmosphere this intact. The usual story is: the neutron star (or pulsar) strips material away from the companion; then, high-energy radiation and particle winds would strip further layers, heat the surface, and possibly strip away or destroy volatile elements or lighter atomic species. Over time you’d expect either atmosphere erosion down to very sparse envelopes, or composition heavily altered by the harsh environment.
But here, despite the pulsar’s intense activity, we see a thick, carbon-dominated atmosphere. That suggests either (a) the planet has somehow retained or acquired this carbon in spite of the stripping, or (b) our models of how black widow companions evolve are missing something important. Some possible explanations include exotic formation histories, mergers, or late delivery of carbon (via, e.g., infalling matter), but none presently explain fully how the extremity of the composition came to be.
Implications & What to Look Forward To
This finding of JWST opens several new lines of inquiry. First, it forces us to reconsider atmospheric chemistry in extreme environments. If carbon can dominate so completely, perhaps other exotic compositions are waiting to be found in similar systems. It also offers a natural laboratory for studying high-temperature chemistry, photochemistry (effects of radiation), and dynamics of atmospheres under intense irradiation.
Second, theories of black widow evolution may need revision. How can an atmosphere survive in such conditions? How do the interactions between the pulsar wind, radiation, and the remnant planet shape structure, composition, and even mass loss over time?
Finally, this demonstrates again how powerful JWST is for exoplanet characterization—not just finding planets, but teasing out their atmospheric composition under bizarre, extreme circumstances. Future observations, especially at different wavelengths or higher resolution, might help map spatial variation (day-night differences), hunt for other molecules, or measure the planet’s mass and radius more precisely.
Discoveries like this compel us to reexamine our theoretical frameworks. They remind us that nature often has surprises in store, ones we might only glimpse when we look hard enough—and with the right tools. As JWST continues its observations, we may find others like it, each widening our sense of what planetary systems can be.
