Lava planet has hydrogen-rich, active atmosphere

Scientists using NASA's James Webb Space Telescope (JWST) have observed the exoplanet 55 Cancri e, revealing a hydrogen-rich atmosphere dominated by carbon monoxide and containing small amounts of carbon dioxide. The findings, published on the arXiv preprint server, challenge previous models of lava planet atmospheres and suggest an active, dynamic environment.

The exoplanet, located 41 light-years away, is tidally locked to its sunlike host star and completes an orbit in just 0.7 days. Its extreme proximity leads to surface melting, creating a lava-rich environment. Researchers analyzed five eclipses of the planet and found evidence of variable atmospheric conditions, including outgassing and transient clouds that could temporarily cool the surface.

The study highlights the connection between a planet's atmospheric composition and its interior redox state. The preference for hydrogen-rich models suggests a low oxygen fugacity, consistent with outgassing from a reduced magma ocean. This finding provides new insights into the formation and evolution of lava exoplanets.

Lava exoplanets, such as 55 Cancri e, K2-141 b, and others, are known for their extreme temperatures and tidal locking. Unlike Io, where volcanism is driven by tidal heating, these exoplanets experience intense heat from their close orbits. The discovery of 55 Cancri e's unique atmosphere adds to the growing understanding of how such planets form and behave, offering a new perspective on planetary science beyond our solar system.