A Lava World with a Cool Face express
A hot skillet on the stove glows in the dark, but if you cover it with a lid, the heat escapes more slowly and the surface doesn't look as bright. That's roughly the situation on planet HD 3167 b: it always shows the same face to its star, and the dayside is heated to temperatures that melt rock. Astronomers expected to see a bare rock radiating heat, but the James Webb Space Telescope showed the planet shining noticeably fainter.
The measurements revealed that the dayside is cooler than a dark, unprotected rock would be. The difference is small — just a few tens of degrees — but enough to suspect the planet has an atmosphere. It could act like a blanket, trapping heat, or like a mirror, reflecting some starlight back into space. The atmosphere also explains why the planet is slightly less dense than expected for a purely rocky sphere.
This discovery matters because astronomers have been debating which hot planets can hold onto atmospheres. HD 3167 b receives less heat from its star than other known lava worlds, yet it still retains a gaseous envelope. That means the boundary beyond which atmospheres disappear lies farther out than previously thought.
Now scientists have a new point on the map: a planet that hasn't completely lost its atmosphere, even though it lives in harsh conditions. The next step is to figure out what that atmosphere is made of, using more detailed observations. Each such find brings us closer to answering how often rocky planets in the universe have air — and thus a chance for life.
If you stood on the dayside of HD 3167 b, you'd see rock melting and flowing like lava from a volcano — while the sky might be filled with clouds of vaporized minerals.
In the series 'The Expanse', colonists live on planets with extreme conditions where the atmosphere becomes a vital resource — HD 3167 b resembles such worlds, where survival depends on a thin gaseous shell.