A bold discovery challenges our understanding of planetary atmospheres. NASA’s Webb telescope has observed an exoplanet with an atmospheric composition so unusual that it defies current formation models, prompting scientists to rethink how such worlds come to be.
Officially named PSR J2322-2650b, this Jupiter-mass planet appears to host a helium- and carbon-dominated atmosphere unlike anything seen before. Soot-like clouds may drift through its air, and deep inside the planet, carbon clouds could condense into diamonds. The origin of this planet remains a mystery. The study is slated for publication in The Astrophysical Journal Letters.
"This was an absolute surprise," remarked co-author Peter Gao of the Carnegie Earth and Planets Laboratory. "After we retrieved the data, our reaction was, ‘What the heck is this?’ It’s strikingly different from our expectations."
PSR J2322-2650b orbits a pulsar, a highly compact and rapidly rotating neutron star. Pulsars emit beams of electromagnetic radiation at precise intervals. These beams are only visible from Earth when their direction aligns with our line of sight, much like a lighthouse beam.
The pulsar in this system is expected to emit primarily gamma rays and other high-energy particles, which Webb cannot see in infrared. The absence of a bright competing star allows scientists to study the planet in exquisite detail over its entire orbit.
"We can view the planet illuminated by its host star while not seeing the star itself," explained Maya Beleznay, a Stanford PhD candidate who helped model the planet’s shape and orbital geometry. "This yields a remarkably clean spectrum and enables deeper study than typical exoplanets."
University of Chicago astronomer Michael Zhang, principal investigator on the project, described the system as extraordinary: a star with solar mass but planet-scale size, hosting a planetary atmosphere composed of molecules like C3 and C2 rather than the usual water, methane, or carbon dioxide.
Molecular carbon is highly unusual at these temperatures because carbon tends to bond with other atoms unless oxygen or nitrogen are nearly absent. The planet’s temperatures vary from about 1,200°F on the night side to roughly 3,700°F on the day side. Out of about 150 studied exoplanets, no others show detectable molecular carbon.
PSR J2322-2650b sits astonishingly close to its star—about 1 million miles away, versus Earth’s 93 million miles from the Sun. Its orbital period is a mere 7.8 hours, and the planet’s shape is distorted into a lemon-like form by intense tidal forces from the heavier pulsar.
Together, the star and planet are sometimes described as a “black widow” system, a rare arrangement where a fast-spinning pulsar erodes a low-mass companion. Traditionally, black widow systems involve a stellar companion; in this case, the companion is classified as an exoplanet, defined by the International Astronomical Union as a body below 13 Jupiter masses that orbits a star, brown dwarf, or stellar remnant such as a pulsar.
Among the roughly 6,000 confirmed exoplanets, this object is the only one resembling a gas giant in a pulsar orbit, making it a singular case among pulsar planets.
"Did this form like a typical planet? Not at all, given its composition," Zhang noted. "Did it form by stripping a star, as seen in canonical black widow systems? Probably not, because nuclear physics doesn’t yield pure carbon. It’s hard to imagine how this highly carbon-enriched makeup could arise, which challenges all known formation scenarios."
Co-author Roger Romani of Stanford and the Kavli Institute suggested a speculative mechanism within this odd atmosphere: as the companion cools, carbon and oxygen in the interior may crystallize, causing pure carbon crystals to rise and mix into the helium layer, producing the observed spectra. Yet keeping oxygen and nitrogen from mixing remains a key puzzle.
"It’s exciting not to know everything," Romani added. "I’m eager to learn more about the weirdness of this atmosphere. It gives us a compelling puzzle to pursue."
A new animation illustrates an exotic exoplanet orbiting a distant pulsar, stretched into a lemon shape by tidal forces at roughly 1 million miles from its host.
Webb’s infrared capabilities and sensitivity enable this kind of discovery, something unattainable from Earth-based observations due to the telescope’s position and its sunshield that keeps instruments cold. Webb, a collaboration led by NASA with ESA and CSA, investigates our solar system, distant worlds around other stars, and fundamental questions about the universe.
For more about Webb, visit: https://science.nasa.gov/webb
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