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Webb Finds Lemon-Shaped Planet Circling a Pulsar With a Helium–Carbon Atmosphere

JWST spectra reveal a helium‑plus‑molecular‑carbon atmosphere that defies existing formation models.

Overview

  • Results published in The Astrophysical Journal Letters detail JWST observations of PSR J2322‑2650b, a Jupiter‑mass companion to a pulsar.
  • The planet orbits roughly a million miles from the pulsar in about 7.8 hours and is tidally distorted into an ellipsoidal, lemon‑like shape.
  • Day–night temperatures span about 650°C to 2,030°C, based on thermal measurements derived from the Webb data.
  • Spectroscopic retrievals show a helium atmosphere rich in molecular carbon (C2, C3) with little or no detectable oxygen or nitrogen, a composition not previously seen on a characterized exoplanet.
  • The system resembles a black‑widow‑type binary with a planet as the companion; researchers propose soot clouds and possible carbon crystallization as hypotheses and note that no accepted formation pathway yet explains the observed chemistry.