A distant planet covered in molten rock has surprised astronomers by showing strong evidence of an atmosphere, despite experiencing extreme temperatures and intense radiation from its host star.
The discovery, made using NASA's James Webb Space Telescope, concerns HD 3167 b, a rocky super-Earth approximately 154 light-years away in the constellation Pisces. The planet completes an orbit around its star in roughly 24 hours.
Published in The Astrophysical Journal Letters in October 2026, the findings could help scientists understand how rocky planets develop and retain atmospheres under exceptionally harsh conditions.
A Planet That Defies Expectations
HD 3167 b belongs to a category known as lava worlds, planets whose intense surface temperatures may be sufficient to melt rock.
Because these planets orbit extremely close to their stars, they experience powerful stellar winds and high-energy radiation capable of stripping away atmospheric gases. Scientists therefore expected many such worlds to have little or no atmosphere.
However, Edwin Kite, an associate professor of geophysical sciences at the University of Chicago and co-author of the study, explained that evidence increasingly suggests some ultra-hot rocky planets can retain atmospheres despite their hostile environments.
He emphasised that understanding these extreme worlds could reveal processes relevant to other rocky planets.
How Webb Detected The Atmosphere
Researchers used a technique called secondary eclipse observation to investigate HD 3167 b. As the planet passes behind its star, the telescope measures the small decrease in infrared light reaching Earth. This allows scientists to estimate how much heat the planet itself emits.
Without an atmosphere, the star-facing side should reach extremely high temperatures because little heat would be transferred to the darker hemisphere.
An atmosphere can redistribute that energy, cooling the illuminated surface. Reflective clouds could produce a similar cooling effect.
Webb's measurements revealed that HD 3167 b was noticeably cooler than expected for an atmosphere-free planet. The result provides strong indirect evidence that the planet possesses an atmosphere, although further observations are needed to confirm its properties.
What Could The Atmosphere Contain?
Scientists initially expected the atmospheres of extremely hot rocky planets to consist mainly of vaporised minerals.
However, emerging evidence suggests that some lava worlds may also contain heavier gases, potentially including carbon dioxide, carbon monoxide or water vapour.
The precise composition of HD 3167 b's atmosphere remains unknown. Researchers suspect its rocky material could resemble the silicate-rich minerals found in Earth's mantle. Future observations may help determine whether its atmosphere contains vaporised rock, other gases or reflective clouds.
Why This Discovery Matters
HD 3167 b is particularly interesting because it is the coolest lava world yet identified with evidence of an atmosphere. Four other ultra-hot rocky planets have previously shown similar indications.
The discovery raises questions about whether a particular temperature threshold influences atmospheric formation or survival.
The findings are part of a wider research programme led by astronomer Megan Mansfield at the University of Maryland, which is examining ten exceptionally hot rocky planets.
By comparing these worlds, scientists hope to identify patterns connecting temperature, atmospheric thickness and heat redistribution.
A Window Into Earth's Distant Past
The research could also provide insights into conditions on Earth billions of years ago. Brandon Park Coy, the study's lead author and a University of Chicago graduate student, explained that studying lava worlds may help scientists reconstruct the earliest stages of terrestrial planet formation.
During Earth's infancy, frequent collisions with developing planetary bodies generated enormous amounts of heat, potentially creating a global ocean of magma.
Although HD 3167 b is far too hot to support life as we know it, its extreme environment may resemble aspects of our planet's distant past.
The Next Step In Planetary Research
Astronomers now hope to collect additional observations to investigate the planet's atmospheric composition and temperature structure. These measurements could help explain why certain rocky planets retain atmospheres while others lose them. The discovery also demonstrates Webb's ability to study distant worlds that cannot be examined directly in conventional images. For scientists exploring planetary evolution, HD 3167 b offers a valuable opportunity to understand how atmospheres behave under extraordinary conditions.
