PSR J2322-2650b is an unprecedented, hot‑Jupiter–mass companion to a millisecond pulsar about 2,055 light‑years away. JWST infrared spectra show a lemon‑shaped, tidally distorted atmosphere heated to ~1,900 K, with winds flowing opposite the planet's spin and an unusual carbon‑dominated chemistry (C2, C3). Researchers propose the object is the eroded remnant of a helium star in a black‑widow–type system, a scenario that challenges standard formation models. Further observations aim to resolve the interior chemistry and evolutionary history.
Lemon-Shaped World: PSR J2322-2650b — A Carbon-Rich Exoplanet Orbiting a Millisecond Pulsar
Ludicrous Lemon-Shaped World Is Like Nothing We've Ever Seen
A newly characterized object in the Milky Way, PSR J2322-2650b, may be one of the strangest planetary‑mass companions astronomers have ever observed. Roughly 80% of Jupiter's mass and located about 2,055 light‑years away, this hot‑Jupiter–class body orbits a millisecond pulsar and is distorted by extreme gravity and intense high‑energy radiation into a lemon‑ or football‑shaped configuration.
Why This System Is Unusual
The host, PSR J2322-2650, is a neutron star spun up into a millisecond pulsar (rotation period ~3.46 ms) that emits powerful radio and gamma beams. Tiny irregularities in the pulsar's radio timing revealed the companion in 2017: a close-in object circling every 7.8 hours. Because the pulsar's emission outshines the system at radio and gamma wavelengths, the James Webb Space Telescope (JWST) — observing in the infrared — provided unusually clean spectra of the companion's illuminated atmosphere.
Key Observational Findings
Extreme heating and shape: Tidal forces and irradiation stretch the atmosphere into a lemon/football shape. Gamma‑ray heating raises atmospheric temperatures to about 1,900 K (~1,630 °C), far hotter than heating by visible starlight alone.
An artist's impression of the bizarre exoplanet and its crazy star. (NASA, ESA, CSA, Ralf Crawford/STScI)
Backwards winds: JWST measurements indicate the atmosphere's winds circulate westward — opposite the planet's eastward spin, which is tidally locked to its orbit. Such retrograde atmospheric flow is highly unusual for close‑in gas giants.
Uncommon chemistry: Instead of the familiar water, methane, or carbon dioxide signatures seen in many exoplanet atmospheres, the spectrum is dominated by molecular carbon species (C2 and C3). Researchers also infer a helium‑rich interior and extreme carbon enrichment that may lead to carbon crystallization ("diamond rain") at depth.
How Could This Object Form?
Surviving a core-collapse supernova as a conventional planet is unlikely. The favored explanation is that PSR J2322-2650b is the remnant of a stellar companion eroded by the pulsar — a so‑called black‑widow scenario. In that process a once‑more massive star is whittled down by the pulsar's energetic output, leaving a low‑mass, non‑fusing object with a helium‑dominated interior and processed, carbon‑rich outer layers.
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"This was an absolute surprise. I remember after we got the data down, our collective reaction was 'What the heck is this?'" — Peter Gao, Carnegie Earth and Planets Laboratory
Not all details are settled. For example, models must explain how oxygen and nitrogen remain depleted while carbon rises and crystallizes in the interior. That unresolved chemistry is the subject of debate and further study.
Why It Matters
This object blurs traditional boundaries between planets, brown dwarfs, and stellar remnants. It demonstrates that compact‑object binaries can produce exotic, planet‑like companions with unfamiliar atmospheres — and that JWST can probe those atmospheres even when the host star is invisible at infrared wavelengths.
Publication: The team's results appear in The Astrophysical Journal Letters. Follow‑up observations are planned to refine atmospheric models and test formation scenarios.
