Astronomers find a diamond-forming, lemon-shaped exoplanet orbiting a pulsar

Surprising Webb Discovery: This Lemon-Shaped Exoplanet Is Rich in Diamonds

A research team using the James Webb Space Telescope has observed a Jupiter-sized exoplanet orbiting a pulsar—and its shape resembles a lemon.

December 17, 2025, 1:30 PM UTC

No larger than a city on Earth yet packing the mass of our Sun—that is the pulsar orbited by a newly discovered exoplanet, spotted by the James Webb Space Telescope. The gravitational forces of the pulsar, at a distance of just 1.6 million kilometers, have warped the Jupiter-sized gas planet into the shape of a lemon.

For context: Earth orbits the Sun at a distance of about 150 million kilometers. But the planet's bizarre shape—and the fact that PSR J2322-2650b is the only known exoplanet of its kind orbiting a pulsar—isn't even what surprised researchers the most.

The real focus is the planet's atmosphere, which is unlike anything seen before. It's no wonder the team reacted to the "absolute surprise" hidden in the data with an exclamation: "What the hell is this?"

"It was completely different from what we expected," said astronomer Peter Gao of the Carnegie Earth and Planets Laboratory in Washington, a co-author of the study published in The Astrophysical Journal Letters. Instead of the usual water, methane, or carbon dioxide found in other exoplanets, the atmosphere of PSR J2322-2650b is dominated by molecular carbon.

This is highly unusual, NASA notes, because at the planet's temperatures, carbon typically bonds with other atoms. The only way it wouldn't is if there were almost no oxygen or nitrogen present—something that rarely, if ever, occurs. Of the 150 planets studied in and beyond our solar system, none have shown detectable molecular carbon.

According to the study, the exoplanet's atmosphere contains not just carbon but also helium. Researchers suspect that soot clouds drift through its skies, potentially compressing inside the planet to form diamonds.

Now, Gao's team, along with lead author Michael Zhang of the University of Chicago, is puzzling over how such a planet could have formed. Under normal conditions, an exoplanet with this kind of atmosphere shouldn't exist.

There's a silver lining: Because the pulsar emits mostly gamma rays and high-energy radiation—both invisible to the Webb telescope—the researchers have an unusually clear view of the exoplanet. The undisturbed spectrum allows for more precise study than would be possible with typical planets, they say.