Webb telescope finds a hydrogen-rich, changeable atmosphere on the lava planet 55 Cancri e

Observations from NASA's James Webb Space Telescope (JWST) have revealed that the scorching rocky exoplanet 55 Cancri e is wrapped in an atmosphere far different from what standard models predicted — one rich in carbon monoxide, containing relatively little carbon dioxide, and surprisingly loaded with hydrogen. The results, reported by a team led by Ignas Snellen and submitted for publication in *Nature Astronomy*, offer a rare glimpse into the chemistry of an alien world's interior (preprint: https://doi.org/10.48550/arXiv.2606.11866; summary at https://www.sciencedaily.com/releases/2026/07/260712011743.htm). 55 Cancri e sits about 41 light-years from Earth, measures roughly 1.88 times Earth's radius and about 8 times its mass, and completes a full orbit of its Sun-like star in only about 0.7 days — compared with Mercury's 88-day year. Because it hugs its star so closely, scientists believe its surface stays hot enough to remain molten rock. The JWST team observed five eclipses of the planet and compared the data with long-standing models of rocky-planet evolution, which had generally forecast atmospheres dominated by carbon monoxide and carbon dioxide (https://doi.org/10.48550/arXiv.2606.11866). Instead, the measurements pointed to abundant carbon monoxide, only small amounts of carbon dioxide, and unexpectedly large quantities of hydrogen. The researchers also found the five eclipse observations differed from one another, a variation they suggest could come from volcanic outgassing or from clouds formed by material vented from the planet's interior. According to the team, such clouds may briefly cool the surface before continued outgassing disperses them (https://www.sciencedaily.com/releases/2026/07/260712011743.htm). The mix of gases is more than a curiosity. A planet's "redox state" — the balance of oxygen against hydrogen and iron in its interior — shapes the atmosphere it outgasses. The preference for hydrogen-rich models, together with the steep temperature inversions they produce, points to an interior with relatively low oxygen availability, consistent with outgassing from a reduced magma ocean. In other words, the atmosphere acts as a window into the chemistry of the planet's depths (https://doi.org/10.48550/arXiv.2606.11866). First identified in 2004, 55 Cancri e is the best-known member of a growing class of "lava exoplanets" — rocky worlds orbiting so near their stars that stellar heat keeps rock molten; other examples include K2-141 b, L 98-59 d, TOI-561 b, HD 63433 d and CoRoT-7 b. Unlike Jupiter's moon Io, whose volcanoes are driven by gravitational tidal heating, these planets are heated mainly by their host stars, and many are tidally locked so that molten regions can stay concentrated on their permanently sunlit side (https://www.sciencedaily.com/releases/2026/07/260712011743.htm). The authors note that as observatories such as JWST continue to study 55 Cancri e and similar worlds, lava planets could reveal more about how the most extreme rocky planets form, evolve and hide their interiors. The paper, "Strong and variable stratospheric CO emission from lava-planet 55 Cnc e observed with NIRCam/JWST," is by Ignas Snellen, Yamila Miguel, Leoni Janssen, Dario Gonzalez Picos, Sam de Regt, Natalie Grasser and Lars Klijn (https://doi.org/10.48550/arXiv.2606.11866).