Scientists using NASA's James Webb Space Telescope have identified PSR J2322-2650b, a Jupiter-mass object orbiting a pulsar at roughly 1 million miles with a 7.8-hour period. Tidal forces from the pulsar deform the body into a lemon-like shape, while JWST spectra show an atmosphere dominated by helium and molecular carbon (C3 and C2). The apparent lack of oxygen and nitrogen and the carbon-rich chemistry have led to debate over whether it is a stripped stellar remnant, a "black widow" companion in final decay, or a new type of object.
Lemon-Shaped Exoplanet Found Orbiting a Pulsar — Strange Carbon-Rich Atmosphere Puzzles Scientists
The oblong exoplanet 'blurs the line between planets and stars'. | Credit: Illustration by Julia Wytrazek / Getty Images
Scientists using NASA's James Webb Space Telescope have discovered an extraordinary exoplanet, PSR J2322-2650b, whose distorted, lemon-like shape and bizarre atmospheric chemistry challenge established ideas about planet formation and atmospheric composition.
Described in a paper published in The Astrophysical Journal Letters and highlighted by the University of Chicago, PSR J2322-2650b has roughly the mass of Jupiter but orbits a pulsar — a rapidly spinning neutron star — at about 1 million miles, completing a full orbit in only 7.8 hours. For context, Earth is roughly 100 million miles from the Sun.
Unusual Host: A Pulsar
Pulsars are ultra-dense stellar remnants that emit narrow beams of radiation, visible when those beams sweep past Earth like a lighthouse. PSR J2322-2650b's proximity to its pulsar and the resulting extreme tidal forces deform the object into an elongated, lemon-like shape.
Extraordinary Atmosphere
Spectroscopic observations with JWST reveal an atmosphere dominated by helium and molecular carbon chains (C3 and C2) instead of the typical signatures such as water, methane, or carbon dioxide. Researchers report possible carbon-soot clouds and the intriguing prospect of carbon condensing into diamond particles that fall as "diamond rain."
Michael Zhang, a coauthor of the study, emphasizes that oxygen and nitrogen — elements normally found alongside carbon — appear conspicuously scarce in this atmosphere, a surprising result that complicates formation theories.
Formation Puzzles and Black Widow Possibility
The planet's composition has prompted several hypotheses. One idea is that PSR J2322-2650b is the stripped remnant of a former star, similar to objects in "black widow" systems where a pulsar gradually erodes a low-mass companion with intense radiation and particle winds. However, researchers note that standard nuclear processes do not easily produce an object composed largely of carbon, so the true origin remains unresolved.
Whether PSR J2322-2650b is a planet being consumed in its final stages, a stellar remnant, or a previously unrecognized class of object, the discovery provides a rare natural laboratory for studying extreme chemistry and the late stages of stellar evolution under conditions very different from those around main-sequence stars.
Next Steps: Follow-up observations with JWST and other telescopes, together with refined theoretical models, will be crucial to verify the atmospheric composition, search for any faint oxygen or nitrogen signals, and test formation scenarios.
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