New observations from NASA’s James Webb Space Telescope suggest that 55 Cancri e, a rocky exoplanet about 41 light-years away, has a hydrogen-rich atmosphere linked to its molten interior. Researchers used the famous telescope to observe five eclipses of 55 Cancri e, then compared the data with existing models of rocky exoplanets.
The results point to an atmosphere shaped by gases escaping from the planet’s interior rather than a static layer surrounding the world. Lava planets have become an increasingly active area of research as more of these scorching worlds have been identified. The new study, submitted toNature Astronomy, focuses on how the atmosphere of 55 Cancri e is connected to the planet’s chemistry beneath its surface.
A Super-Earth Orbiting So Close that Rock May Melt
55 Cancri e is about 1.88 times Earth’s radius and roughly eight times more massive. It circles a Sun-like star once every 0.7 days and is tidally locked, so the same side always faces its star. NASA says the planet’s orbit is so tight that temperatures may be high enough to melt parts of its surface.
To study the planet, scientists observed five secondary eclipses with JWST. They compared those observations with long-standing models that predict what the atmospheres of lava worlds should look like. The study, published in arXiv,reports that these models generally expect large amounts of carbon monoxide, and carbon dioxide.
Instead, the observations suggest an atmosphere made mostly of carbon monoxide, along with smaller amounts of carbon dioxide and abundant hydrogen. The paper also notes that the differences seen during the five eclipses may be caused by outgassing or by clouds formed from those gases. Those clouds could briefly cool the surface before disappearing as fresh gases are released.
Below the Surface Revealed
The gases detected around 55 Cancri e may reveal what is happening deep inside the planet, offering scientists a direct glimpse into the chemistry of its molten interior.
“Since secondary atmospheres of rocky planets are set by the composition of the interior and subsequent outgassing, the composition of their atmospheres is directly linked to their interior redox states,” the researchers write.
The source also explained that that its interior contains much more hydrogen than oxygen.
“The preference for hydrogen-rich models, together with the steep inversions they produce, therefore suggests an interior with relatively low oxygen fugacity, consistent with outgassing from a reduced magma ocean.”
The authors indicates that this chemical balance matches the atmosphere detected by JWST and supports the idea that gases escaping from the molten interior continue to shape its atmosphere.
Lava Worlds Are Becoming Easier To Study
Although 55 Cancri e was discovered in 2004, it is now part of a growing group of known lava exoplanets. The source lists K2-141 b, L 98-59 d, TOI-561 b, HD 63433 d and CoRoT-7 b among the other planets in this category.
All of them orbit extremely close to their stars and are tidally locked, exposing them to intense heat. Their orbital periods range from about 6.7 hours to 7.5 days. Like 55 Cancri e, these ones experience temperatures high enough to create vast molten regions. The source notes that while 55 Cancri e likely has lava concentrated on its star-facing side, planets such as L 98-59 d may be covered by a global magma ocean.
These planets differ from Jupiter’s moon Io. Io’s volcanoes are powered by tidal heating created by Jupiter’s gravity, while lava exoplanets owe their volcanic activity to the intense heat generated by orbiting extremely close to their host stars.
