The James Webb Space Telescope (JWST) has uncovered a planet that defies traditional planetary formation theories, revealing an atmosphere predominantly made of carbon. This discovery, detailed in a recent preprint study on arXiv, challenges existing models of planet formation and could signal a significant shift in our understanding of the universe.
Researchers focused on an exoplanet orbiting the millisecond pulsar known as PSR J2322-2650, part of a unique class of systems referred to as “black widow” pulsars. These pulsars are known for their intense gravitational pull, which allows them to draw material from a nearby companion star. Over time, the pulsar”s powerful forces strip away the outer layers of this star, leaving a dense remnant.
In this case, the companion star has likely transformed into a “hot Jupiter,” completing an orbit around the neutron star every 7.8 hours. This two-stage process typically results in a helium-rich planet, but the findings regarding this specific exoplanet, designated PSR J2322-2650b, are unexpected.
While the size and density of PSR J2322-2650b align with other Jupiter-like remnants, JWST”s spectral data revealed that its atmosphere is composed mainly of elemental carbon. This carbon is present in molecular forms like tricarbon (C3) and dicarbon (C2), which are not typically associated with planetary atmospheres but rather found in cometary tails and flames on Earth.
Intriguingly, the planet”s day side, which is perpetually oriented toward the pulsar due to tidal locking, experiences extreme temperatures exceeding 2000 °C and exhibits distinct chemical signatures. Conversely, the night side shows minimal features, indicating it may be covered in a layer of soot or a similar substance devoid of unique characteristics.
Further analysis of the atmospheric composition revealed a striking carbon-to-oxygen ratio exceeding 100 and a carbon-to-nitrogen ratio above 10,000. For comparison, Earth has a carbon-to-oxygen ratio of 0.01 and a carbon-to-nitrogen ratio of 40, underscoring the unusual abundance of carbon on this planet.
This discovery poses a significant puzzle for planetary formation theories, particularly the black widow model, which suggests that the outer layers of planets would be stripped away by the companion star”s radiation or gravitational pull. The existence of such a carbon-rich atmosphere raises questions about how these conditions could persist.
While there are potential processes that could lead to such an atmosphere, like a merger of white dwarfs from carbon-rich stars, these theories do not fully account for the planet”s high carbon-to-oxygen ratio. However, certain characteristics of the planet do align with existing theories. For instance, circulation models predict that rapidly rotating planets like PSR J2322-2650b would have strong westerly winds, contrasting with the easterly winds typically observed on other hot Jupiters. The data from JWST indicate that the hottest part of the planet is approximately 12 degrees west of center, marking the first observational evidence of this western wind phenomenon.
The findings from PSR J2322-2650b illustrate the complexity and variability of planetary atmospheres and underline the necessity for scientists to revisit and refine current models of planetary formation. As researchers continue to analyze these unexpected results, the JWST will keep scanning the cosmos for more anomalies that may prompt further scientific revolutions.
Reference: “A Carbon-rich atmosphere on a windy pulsar planet” by Michael Zhang, et al., 11 September 2025, arXiv. DOI:10.48550/arXiv.2509.04558
