Astronomers using NASA’s James Webb Space Telescope have characterized a remarkable exoplanet with an unusual lemon shaped appearance. Designated PSR J2322-2650b, this Jupiter-mass world orbits a rapidly spinning neutron star known as a pulsar. Strong gravitational tides from the compact host stretch the planet into a distinctive lemon shaped exoplanet, marking it as one of the most deformed worlds observed to date.
The lemon shaped exoplanet completes an orbit around its pulsar every 7.8 hours, at a distance of approximately 1 million miles. This extremely close proximity subjects the planet to intense tidal forces, elongating its gaseous body into a prolate form. Day-side temperatures reach up to 3,700 degrees Fahrenheit, while the night side cools to about 1,200 degrees Fahrenheit. Pulsar planets are exceedingly rare, with only a handful confirmed to date, most of which are small terrestrial bodies. This discovery represents the first known Jupiter-mass gaseous planet orbiting a pulsar.
Observations with the James Webb Space Telescope revealed an atmosphere dominated by helium and carbon, featuring detectable molecular carbon species such as C2 and C3. Soot-like carbon particles form clouds. Researchers suggest that in deeper layers, extreme pressures could compress carbon into diamonds, though this remains a hypothesis requiring further confirmation. The composition lacks significant oxygen or nitrogen, resulting in an environment enriched purely in carbon. As detailed in a NASA press release, the pulsar’s emission is negligible in the infrared wavelengths observed by Webb, enabling a clear transmission spectrum of the planet’s atmosphere without significant contamination from the host.
Lead author Michael Zhang noted the uniqueness of this finding. “This is a new type of planet atmosphere that nobody has ever seen before,” he said. Co-author Peter Gao described the initial reaction to the data. “This was an absolute surprise. Our collective reaction was ‘What the heck is this?'” The observations highlight how the pulsar’s minimal infrared output allowed a pristine view of the illuminated planet.
The formation of this lemon shaped exoplanet remains puzzling. Known pulsar planets typically arise from disrupted companions or remnant disks, but none predict such extreme carbon enrichment. The system resembles a black widow pulsar, where the neutron star evaporates its companion, yet the planetary mass and composition do not fit standard stripping models. Maya Beleznay emphasized the observational advantage. “We get a really pristine spectrum,” she said.
This discovery expands understanding of extreme exoplanetary environments around dead stars. Further studies with Webb may clarify the processes shaping such bizarre worlds.
A related study appears in The Astrophysical Journal Letters
References
NASA. (2025, December 16). NASA’s Webb observes exoplanet whose composition defies explanation. NASA Science. https://science.nasa.gov/missions/webb/nasas-webb-observes-exoplanet-whose-composition-defies-explanation/
Zhang, M., et al. (2025). A Carbon-rich Atmosphere on a Windy Pulsar Planet. The Astrophysical Journal Letters, 961(1), L18. https://doi.org/10.3847/2041-8213/ae157c
University of Chicago News. (2025). NASA’s Webb telescope finds bizarre atmosphere on a lemon-shaped exoplanet. https://news.uchicago.edu/story/nasas-webb-telescope-finds-bizarre-atmosphere-lemon-shaped-exoplanet