When life gives you lemons, make... a planet!
- Eduarda Tomio
- Dec 10, 2025
- 3 min read
Updated: 13 hours ago
In December 2025, the James Webb Space Telescope (JWST) captured a lemon-shaped exoplanet, officially named PSR J2322-2650b. The planet raised multiple questions among scientists due to its previously unobserved atmospheric composition. Based on this distinct feature, further research is needed to better understand the planet's origin.
Exoplanet PSR J2322-2650b (left) and pulsar (right): artist's conception image copyright
and credit to NASA, ESA, CSA, Ralf Crawford (STScI)
About The System
A new exoplanet — a planet located outside the Solar System — is orbiting a pulsar, a rapidly spinning neutron star. That type of duo isn't what makes it unique, seeing that the first exoplanets confirmed followed the same settings. However, the planet's shape, similar to a lemon, and the carbon- and helium-dominated atmosphere are unprecedented. Together, they form an unconventional "black widow” system: a rapidly spinning pulsar paired with a small, low-mass stellar companion. In this case, the pulsar is paired with a planet rather than a star, a configuration that is rare but not unprecedented. In the spider named system, the pulsar would slowly consume its companion.
Lemon Shape
PSR J2322-2650b is a Jupiter-mass planet, and the weird star it orbits has the size of a city while holding the mass of our Sun. Adding to that, they are an extremely close system, with a distance of 1 million miles, 100 times closer than Earth is to the Sun. That extraordinary proximity results in the planet's year being less than 8 hours. Additionally, the differences in distance and size generate gravitational forces that lead to the unconventional lemon shape.
Atmosphere
Usually, scientists cannot observe a planet's composition in such detail because its star companion outshines it. In this case, however, the star is almost invisible, allowing us to study the exoplanet. The planet can't outshine a star, as it doesn't generate light on its own, since light comes from the star's nuclear fusion. We can see the planet but not the star because JWST primarily detects infrared light, whereas the pulsar emits high-energy particles, primarily gamma rays. Such frequencies are not covered by the telescope, allowing a more accurate study of PSR J2322-2650b.
Michal Zhang, University of Chicago's main investigator on the study of this planet, says, “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 (CO2) — we saw molecular carbon." The planet's temperature ranges from 1200 to 3700 degrees Fahrenheit, which makes the presence of molecular carbon unusual, as carbon would bind to other atoms in the atmosphere under these conditions. Molecular carbon is only dominant if there is no oxygen or nitrogen. No known formation mechanism leads to such a carbon-enriched composition.
PSR J2322-2650b origin
The planet couldn't have undergone normal planetary formation due to its unique composition. Neither could it have undergone a similar formation of a "normal” black widow, given that its pure carbon can't be produced by nuclear processes. Roger Roman (Stanford University and the Kavli Institute for Particle Astrophysics and Cosmology) proposes an evocative phenomenon: an action that evokes a response from others in an environment. The idea is that as the pulsar cools, mixed carbon-oxygen crystals begin to crystallize, and pure carbon crystals float, mixing with helium at the top. That is a process we can observe, but the lack of mixing between oxygen and nitrogen remains a mystery.
Related Links:
Space.com: https://www.space.com/astronomy/exoplanets/james-webb-space-telescope-discovers-a-lemon-shaped-exoplanet-unlike-anything-seen-before-what-the-heck-is-this
University of Chicago: https://news.uchicago.edu/story/nasas-webb-telescope-finds-bizarre-atmosphere-lemon-shaped-exoplanet
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