NASA’s James Webb Space Telescope has observed an oddly shaped exoplanet with an atmosphere so unusual that scientists are struggling to explain its strange composition.
Among the unusual features of PSR J2322-2650b’s exotic atmosphere are what appear to be clouds of soot that may condense into diamonds. Astronomers revealed their investigation of the exoplanet’s helium and carbon-rich atmosphere in a recent paper published in The Astrophysical Journal Letters.
“This was an absolute surprise,” said study co-author Peter Gao of the Carnegie Earth and Planets Laboratory. “I remember after we got the data down, our collective reaction was ‘What the heck is this?’ It’s extremely different from what we expected.”
An Excellent Exoplanet View
Fortunately for the astronomers studying this strange Jupiter-mass planet, its cosmic environment provides optimal conditions for observation, as its host object is a rapidly rotating pulsar. Such stars produce brilliant beams of electromagnetic radiation, but these emissions are brief and can only be detected when aimed directly at an observer.
Those millisecond-long bursts consist of gamma rays and other high-energy particles that do not appear in the James Webb Space Telescope’s infrared images. This leaves only a tiny and relatively dim source between astronomers and PSR J2322-2650b, enabling an unusually clear view of the exoplanet’s entire orbit. A notable feature of the pulsar is its extremely high mass-to-radius ratio, which leaves little to obscure observations as the planet passes behind it from our perspective.
“This system is unique because we are able to view the planet illuminated by its host star, but not see the host star at all,” said co-author Maya Beleznay, a PhD candidate at Stanford University. “So we get a really pristine spectrum. And we can study this system in more detail than normal exoplanets.”
Molecular Carbon Atmosphere
“The planet orbits a star that’s completely bizarre — the mass of the Sun, but the size of a city,” said lead author Michael Zhang, of the University of Chicago. “This is a new type of planet atmosphere that nobody has ever seen before. Instead of finding the normal molecules we expect to see on an exoplanet — like water, methane, and carbon dioxide — we saw molecular carbon, specifically C3 and C2.”
PSR J2322-2650b’s temperatures range from 1,200 °F to 3,700 °F. At such extremes, carbon would typically bond with other elements rather than with other carbon molecules. None of the roughly 150 previously studied exoplanets have displayed a molecular carbon–dominated atmosphere, which would be expected only in the near-total absence of oxygen or nitrogen.
The exoplanet also orbits extremely close to its host star, at a distance only one one-hundredth that of Earth’s orbit around the Sun. An entire year on PSR J2322-2650b lasts just 7.8 Earth hours, with the intense gravitational forces generated by its tight orbit squeezing the planet into an unusual lemon-like shape.
James Webb Space Telescope Spies More Unusual Features
Very few pulsars are known to host planets, and none have previously been observed hosting a hot Jupiter. Another unusual aspect of the system is that it qualifies as a black widow system, which typically consists of two stars rather than a star and a planet. In such arrangements, the pulsar acts as the black widow, pulling material from its companion to generate a powerful stellar wind that eventually destroys it.
“Did this thing form like a normal planet? No, because the composition is entirely different,” said Zhang. “Did it form by stripping the outside of a star, like ‘normal’ black widow systems are formed? Probably not, because nuclear physics does not make pure carbon. It’s very hard to imagine how you get this extremely carbon-enriched composition. It seems to rule out every known formation mechanism.”
The team has proposed one theory that may begin to explain the exoplanet’s strange characteristics.
“As the companion cools down, the mixture of carbon and oxygen in the interior starts to crystallize,” said co-author Roger Romani, of Stanford University. “Pure carbon crystals float to the top and get mixed into the helium, and that’s what we see. But then something has to happen to keep the oxygen and nitrogen away.”
Although a few mysteries remain, Romani says that is part of what makes the team’s discoveries so intriguing.
“It’s nice to not know everything,” Romani added. “I’m looking forward to learning more about the weirdness of this atmosphere.”
“It’s great to have a puzzle to go after.”
The paper, “A Carbon-rich Atmosphere on a Windy Pulsar Planet,” appeared in The Astrophysical Journal Letters on December 16, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.