A handful of enigmatic Jupiter-mass objects have been discovered orbiting pulsars. One such object, PSR\,J2322-2650b, uniquely resembles a hot Jupiter exoplanet due to its minimum density of 1.8 g/cm^3 and its ~1900 K equilibrium temperature. We use JWST to observe PSR J2322-2650b's emission spectrum across an entire orbit. In stark contrast to every known exoplanet orbiting a main-sequence star, we find an atmosphere rich in molecular carbon (C3, C2) with strong westward winds. Our observations open up new exoplanetary chemical (ultra-high C/O and C/N ratios of >100 and >10,000, respectively) and dynamical regimes (ultra-fast rotation with external irradiation) to observational study. The extreme carbon enrichment poses a severe challenge to the current understanding of ``black widow'' companions, which were expected to consist of a wider range of elements due to their origins as stripped stellar cores.
@article{arxiv.2509.04558,
title = {A carbon-rich atmosphere on a windy pulsar planet},
author = {Michael Zhang and Maya Beleznay and Timothy D. Brandt and Roger W. Romani and Peter Gao and Hayley Beltz and Matthew Bailes and Matthew C. Nixon and Jacob L. Bean and Thaddeus D. Komacek and Brandon P. Coy and Guangwei Fu and Rafael Luque and Daniel J. Reardon and Emma Carli and Ryan M. Shannon and Jonathan J. Fortney and Anjali A. A. Piette and M. Coleman Miller and Jean-Michel Desert},
journal= {arXiv preprint arXiv:2509.04558},
year = {2025}
}