JWST Confirms Exoplanet Orbiting Pulsar Possesses a Carbon-Dominated Atmosphere

Scientists utilizing data from NASA's James Webb Space Telescope (JWST) have confirmed the existence of the exoplanet PSR J2322-2650b, whose atmosphere presents a significant anomaly when measured against current planetary formation models. This groundbreaking research, which details the discovery, has been accepted for publication in The Astrophysical Journal Letters, scheduled for December 2025. The lead author, Michael Zhang of the University of Chicago, highlighted that the research team detected a planetary atmospheric type previously unseen in astronomical records. This breakthrough was made possible by the JWST’s exceptional infrared sensitivity, operating from its stable vantage point millions of miles from Earth.

The celestial body, PSR J2322-2650b, orbits a pulsar star that possesses a mass comparable to our Sun but is compressed to the size of a city. The planet maintains an extremely close proximity to its host star—approximately one million miles. Due to the pulsar's immense gravitational pull, the planet, which has a mass similar to Jupiter, is significantly distorted into a lemon-like shape. Its orbital period is remarkably short, clocking in at just 7.8 hours, underscoring its incredibly tight orbit. The intense radiation emitted by the pulsar, primarily composed of gamma rays and other high-energy particles, does not impede the Webb telescope's infrared detectors, allowing for clear spectral tracking throughout the entire orbit.

Data gathered by the Webb instrument revealed an atmosphere overwhelmingly dominated by helium, alongside molecular carbon compounds C3 and C2. This observation is unprecedented; among the roughly 150 exoplanet atmospheres studied to date, no other has shown detectable molecular carbon. This composition is highly unusual for a world experiencing surface temperatures exceeding 2,000 degrees Celsius, especially given the observed scarcity of oxygen and nitrogen. Maya Belesnay from Stanford University, who modeled the planet's geometry, emphasized that this configuration offers an exceptionally 'pristine' spectrum ideal for detailed analysis.

The research team posits that the extreme internal pressure within the planet might be compressing the carbon into a diamond-like state. Zhang commented that this unique chemical structure challenges existing planet formation theories, as it is difficult to rationalize how such a carbon-rich composition could have developed, seemingly ruling out known formation mechanisms. While the system is classified as a 'black widow' binary, Zhang argued that PSR J2322-2650b does not fit the standard scenarios for remnants resulting from stellar mass ejection, noting that nuclear physics does not typically yield pure carbon. Roger Romani, also from Stanford University, put forth an alternative theory involving the internal crystallization of carbon and oxygen, which would result in pure carbon migrating to the surface.

Prior investigations, conducted using the Gemini South telescope in Chile, initially identified this object, which is part of a 'black widow' system where the pulsar is gradually consuming its companion star. Michael Zhang, who secured the Suzuki Postdoctoral Fellowship in January 2025, had previously been engaged in analyzing JWST data at the University of Chicago. Scientists, including Peter Gao from the Carnegie Earth and Planets Laboratory, candidly shared the team's initial reaction to the findings: “What the heck is that?” This confirmation of a planet orbiting the millisecond pulsar PSR J2322-2650 opens an entirely new frontier in our comprehension of exotic planetary environments.