December 17, 2025
2 min read
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This Planet Is the Shape of a Lemon. That May Be the Least Weird Thing about It
Astronomers using the James Webb Space Telescope have discovered a bizarre-looking exoplanet that defies explanation
Image courtesy of NASA/ESA/CSA/Ralf Crawford/STScI
Astronomers have discovered a bizarre lemon-shaped exoplanet orbiting a dense, rapidly spinning dead star. But those details are perhaps the least weird thing about it.
Using the James Webb Space Telescope, astronomers found that the planet’s atmosphere is enriched in carbon—but devoid of nitrogen and oxygen. That matters because “everywhere in the universe, where there’s carbon, there tends to be nitrogen and oxygen,” says Michael Zhang, a postdoctoral researcher at the University of Chicago and a co-author of a preprint paper detailing the findings that will be published in the Astrophysical Journal Letters.
Dubbed PSR J2322-2650b, the Jupiter-mass gas giant planet orbits a kind of small, dense star known as a pulsar, which pulses jets of electromagnetic radiation from its poles at regular intervals—much like a lighthouse beams out light. When Zhang and his colleagues observed the so-called emission spectrum of the planet’s atmosphere, they found wavelengths that corresponded with molecular carbon, which they believe could also be at the planet’s core in the form of diamonds.
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Because PSR J2322-2650b is big enough and close enough to its pulsar host, the star’s gravity is pulling the planet into a lemon shape. Astronomers know of other gas giant exoplanets orbiting ordinary stars that are distorted but to a far lesser degree, Zhang says.
The bigger mystery, however, is how this planet formed at all, given its strange atmosphere. “It’s really hard to explain by conventional means,” Zhang says. One explanation is that the planet is itself the stripped remains of a former star—but that doesn’t solve the missing oxygen and nitrogen mystery, he says.
“I’m open to the possibility that this is an entirely new type of object,” Zhang says.
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