Summary
NASA’s jwst observed five eclipses of 55-cancri-e, a tidally locked super-Earth (~1.88 R⊕, ~8 M⊕) orbiting a sun-like star every 0.7 days at ~41 light-years. Contrary to prior lava-planet models, ignas-snellen et al. find the atmosphere is hydrogen- and CO-rich with minor CO₂ — not the carbon-oxide-dominated composition expected for lava planets. Variable eclipse depths across the five observations are interpreted as active outgassing or transient cloud cycles driven by outgassing. The planet’s low oxygen-fugacity interior is proposed as the driver of this secondary-atmosphere composition. The result adds 55 Cnc e to a growing lava-planet catalogue alongside l-98-59-d, K2-141 b, and CoRoT-7 b, while establishing that oxygen-fugacity-controlled outgassing governs secondary-atmosphere diversity.
Key Claims
- Atmosphere likely composed of large amounts of CO and hydrogen, small amounts of CO₂ — contradicts carbon-oxide lava-planet models (Snellen et al., arXiv 2606.11866, submitted to Nature Astronomy)
- Mixed eclipse depths across five JWST observations indicate active outgassing or clouds forming from outgassing (Snellen et al.)
- Interior low oxygen fugacity supports hydrogen-rich secondary-atmosphere outgassing (Snellen et al.)
- All known lava exoplanets are tidally locked with extreme dayside temperatures (Snellen et al.)
- 55 Cnc e: ~1.88 R⊕, ~8 M⊕, 0.7-day orbit, tidally locked, sun-like host star at ~41 ly
Notable Quotes
“The atmosphere is likely composed of large amounts of CO and small amounts of CO2, while also having large amounts of hydrogen.” — Snellen et al.
“Mixed data among the five eclipses could be indicative of outgassing or clouds forming from the outgassing.” — Snellen et al.