NASA’s James Webb Space Telescope reveals a strange atmosphere on a hellish lava planet

Astronomers using NASA’s James Webb Space Telescope have made unusual observations of 55 Cancri e, a super-Earth located approximately 41 light years from Earth. The planet, which measures roughly 1.88 Earth radii and possesses about 8 Earth masses, orbits its host star in only 0.7 days—far faster than Mercury’s 88-day orbital period around our Sun. Due to its proximity to its star, scientists believe the planet’s surface remains molten.

Observations from five eclipse events detected by JWST revealed an atmospheric composition that diverges from long-standing theoretical predictions. While models had generally forecast atmospheres dominated by carbon monoxide and carbon dioxide, the actual observations indicated abundant carbon monoxide alongside relatively modest amounts of carbon dioxide but surprisingly substantial quantities of hydrogen. Variations observed among the five eclipse observations suggest possible contributions from volcanic outgassing or cloud formation generated by material originating from the planet’s interior. According to researchers, these clouds may provide temporary surface cooling before subsequent outgassing disperses them.

The hydrogen-rich atmospheric composition reflects the planet’s interior chemistry, specifically its redox state—the chemical balance between oxygen and hydrogen within the planetary interior. The findings indicate that hydrogen is strongly favored over oxygen in 55 Cancri e’s composition, consistent with outgassing from a reduced magma ocean. This atmospheric profile offers a rare opportunity to examine the deep interior chemistry of an exoplanet through observable characteristics at its surface.

Lava exoplanets have become an increasingly common focus of astronomical research over the past decade. Examples include K2-141 b, L 98-59 d, TOI-561 b, HD 63433 d, and CoRoT-7 b, many of which are tidally locked to their stars and experience extreme temperatures. Unlike Jupiter’s moon Io, whose volcanism results from tidal heating caused by gravitational forces, lava exoplanets are heated primarily through proximity to their host stars. The research findings, submitted for publication in Nature Astronomy, may provide valuable understanding of how such extreme worlds form and evolve.