Bold claim: Even in the furnace of an ultra-close orbit, a rocky exoplanet may still cradle an atmosphere. The James Webb Space Telescope (JWST) has delivered the strongest hint yet that TOI-561 b—a compact, Earth-sized world veering perilously close to its star—could possess air. This is a surprising possibility that challenges assumptions about how atmospheres endure around planets baked by starlight.
TOI-561 b is a small world, less than 1.5 times the diameter of Earth, completing an orbit around its G-type (Sun-like) host star in under 11 hours. Its proximity is extreme: at a distance under 1 million miles from its star, one hemisphere is perpetually sunlit, forming a scorching lava ocean that bathes the planet in heat.
What astonished researchers is the planet’s low density.
“You can see the standout feature here: TOI-561 b is unusually low in density,” said Johanna Teske of the Carnegie Institution for Science’s Earth and Planets Laboratory, who led the study. “It isn’t a super-puff, but it’s less dense than you’d expect if it shared Earth-like composition.” If TOI-561 b does harbor an atmosphere, it would imply that rocky exoplanets under extreme conditions can retain air, offering fresh clues for the ongoing search for habitable worlds beyond our solar system.
Initially, scientists considered whether the planet’s composition might be unusual, given its 280-light-year distance from Earth and its old, iron-poor star. While the star is similar to the Sun, its growth environment hints at chemistry akin to early-universe planets. Yet this alone could not explain the JWST observations.
The team then explored the possibility that TOI-561 b has a substantial atmosphere. To test this, Webb tracked the planet’s infrared glow as it passed behind its star (a secondary eclipse). This technique helps determine surface temperatures by measuring heat emission, which would differ dramatically between a bare rock and a world with a thick atmosphere.
If TOI-561 b were a barren rock with no atmosphere, its dayside temperature would be around 4,900°F. Instead, Webb found a cooler, though still blistering, surface temperature near 3,200°F. These measurements, reported in The Astrophysical Journal Letters, point toward atmospheric cooling processes and heat redistribution.
An atmosphere could drag heat away via strong winds that shuttle warmth to the planet’s dark side. Gases like water vapor might trap some heat, keeping the dayside cooler than expected. Additionally, reflective clouds formed from rock-like particles could bounce some starlight away, further reducing observed temperatures.
To unlock the planet’s full story, the researchers plan more observations to map temperatures across TOI-561 b’s surface and determine its atmospheric composition. A key question remains: how can such a small planet retain an atmosphere so close to a blazing star? One intriguing idea is a continuous exchange of gases between a magma ocean and the surrounding air—a kind of lava–gas cycle that sustains atmospheric buffering.
“TOI-561 b appears to be far more volatile-rich than Earth,” commented Tim Lichtenberg, a coauthor. “It’s almost a molten, water-rich ball of rock.” This discovery opens the door to new theories about atmospheric retention in extreme environments and reframes what is possible for rocky worlds in harsh stellar neighborhoods.
Would you expect a tiny, scorching planet to hold onto an atmosphere, or do you think any air would be fleeting under such conditions? Share your thoughts below as scientists continue to refine their measurements and models.
