Space
Webb finds a surprise in the atmosphere of a lava world 41 light-years away
Imagine a planet where the ground is a roiling ocean of molten rock and the "day" lasts less than 18 hours. That is 55 Cancri e, a super-Earth orbiting a Sun-like star about 41 light-years from us. New observations from NASA's James Webb Space Telescope have revealed something unexpected: this inferno is wrapped in a hydrogen-rich atmosphere, fed by gases escaping from its liquid interior.
A planet that should not hold onto air
55 Cancri e is roughly 1.88 times Earth's radius and about eight times its mass — a "super-Earth" larger than our world but smaller than Neptune. It hugs its star so tightly that a full orbit takes only about 0.7 days, and its sun-facing surface stays hot enough to keep rock in a liquid, lava-like state. Standard thinking says a planet this close to its star, and this hot, should have been stripped of any atmosphere long ago by the relentless stellar wind.
Yet when Webb watched the planet pass behind its star five times and recorded the light filtering through its edge, the spectrum told a different story. The data strongly favor hydrogen over oxygen, pointing to a atmosphere rich in hydrogen — possibly with carbon monoxide mixed in — rather than the oxygen-dominated air we might expect from a rocky world.
Why hydrogen, and why does it survive?
The leading explanation is elegant: the planet's global lava ocean is not just scenery, it is the source. As silicates churn in the molten surface, they release gases that rise to form a thin but persistent atmosphere. In this picture, the air is continuously replenished from below, so even if the star blows some of it away, the planet simply makes more. The hydrogen-rich blanket may even help redistribute heat from the permanently roasted day side to the cooler night side.
This resolves a puzzle from earlier studies, which had hinted at an atmosphere but could not pin down its composition. The new results line up with computer simulations showing that a hydrogen-rich shell supported by a lava ocean can explain the planet's observed properties.
Why a lava world matters
It is the best testbed for rocky-planet atmospheres. 55 Cancri e is the closest known super-Earth and one of the few where we can actually probe a rocky planet's air. Every measurement sharpens our models of how atmospheres form, survive, and evolve.
It rewrites the "too hot for air" rule. If a planet this extreme can keep an atmosphere alive through outgassing, then other hot rocky worlds — and perhaps rocky planets nearer the habitable zone — may be far more atmospherically diverse than we assumed.
It trains the telescope for the big questions. Techniques refined here, from eclipse spectroscopy to atmosphere modeling, are exactly what we will need when Webb and its successors turn toward planets that might resemble early Earth.
55 Cancri e will not host life, but as a natural laboratory it is priceless: a place where the boundary between a planet's molten heart and its sky turns out to be far more porous — and far more interesting — than anyone expected.