NASA's James Webb Space Telescope has revealed a strange atmosphere on a hellish lava planet, offering a glimpse into the extreme world of 55 Cancri e. This super Earth, located about 41 light years from Earth, has a hydrogen-rich atmosphere, which is surprising given the planet's proximity to its star and the expected composition of its interior. The findings, submitted for publication in Nature Astronomy, could provide valuable insights into how lava exoplanets form and evolve.
The research team observed five eclipses of 55 Cancri e with JWST and compared the results with long-standing models of rocky exoplanet evolution. These models generally predicted atmospheres rich in carbon monoxide (CO) and carbon dioxide (CO2). However, the new observations point to an atmosphere containing abundant carbon monoxide, relatively small amounts of carbon dioxide, and surprisingly large amounts of hydrogen.
The researchers also found differences among the five eclipse observations, suggesting volcanic outgassing or clouds formed from material released by the planet's interior. These clouds may temporarily cool the planet's surface before continued outgassing disperses them. The study notes that the composition of the atmosphere is directly linked to the planet's interior redox state, indicating a relatively low oxygen fugacity and a reduced magma ocean.
A planet's redox state describes the chemical balance between oxygen and hydrogen/iron within its interior. For 55 Cancri e, the results indicate that hydrogen is strongly favored over oxygen, helping explain why the planet appears to possess a hydrogen-rich atmosphere. This atmosphere can reflect what is happening deep inside the planet, offering a rare window into the chemistry of an alien world's interior.
Lava exoplanets, like 55 Cancri e, are becoming increasingly common as more of these extreme worlds are discovered. Other known lava exoplanets include K2-141 b, L 98-59 d, TOI-561 b, HD 63433 d, and CoRoT-7 b. These planets are tidally locked to their host stars and endure extraordinary temperatures, with molten rock concentrated on the permanently sunlit side.
While Io and lava exoplanets can both feature extensive volcanism, the forces driving that activity are very different. Io's volcanoes are powered by tidal heating, while lava exoplanets are heated primarily by their proximity to their host stars. As astronomers continue using powerful observatories like JWST, 55 Cancri e and other lava worlds could reveal even more about the formation, evolution, and hidden interiors of some of the most extreme rocky planets ever discovered.
