Astronomers using NASA’s James Webb Space Telescope have found the strongest evidence yet that a rocky planet outside our solar system can hold on to an atmosphere—even under some of the most extreme conditions known.
The planet, called TOI-561 b, is an ultra-hot “super-Earth” so close to its star that its surface is likely covered by a global ocean of molten rock.
The discovery, published in The Astrophysical Journal Letters, challenges the long-held idea that small, rocky planets orbiting very close to their stars must be airless, stripped bare by intense radiation.
Instead, TOI-561 b appears to be wrapped in a thick blanket of gases that helps regulate its temperature and explains why it is surprisingly low in density.
TOI-561 b is a strange and extreme world. It is about 1.4 times the size of Earth but orbits its star in less than 11 hours, placing it in a rare group known as ultra-short-period exoplanets.
Although its host star is only slightly smaller and cooler than our Sun, the planet orbits less than one million miles away—about one-fortieth the distance between Mercury and the Sun.
At such close range, TOI-561 b is tidally locked, meaning one side always faces the star while the other remains in permanent darkness.
The dayside temperature is expected to be high enough to melt rock, creating a vast magma ocean. For years, scientists assumed planets like this would be bare, glowing rocks with no atmosphere left after billions of years of intense stellar heating. But Webb’s observations tell a different story.
Using Webb’s Near-Infrared Spectrograph, researchers measured the planet’s heat by watching what happens when it passes behind its star. When the planet disappears from view, the total light from the system drops slightly, allowing scientists to estimate how hot the planet’s dayside is.
If TOI-561 b had no atmosphere, its dayside temperature should be close to 4,900 degrees Fahrenheit, or about 2,700 degrees Celsius. Instead, Webb measured a temperature closer to 3,200 degrees Fahrenheit, or 1,800 degrees Celsius. That is still unimaginably hot, but far cooler than expected for a bare rock.
The most likely explanation is a thick, volatile-rich atmosphere. Gases such as water vapor could absorb some of the heat before it escapes into space, making the planet appear cooler.
Strong winds could also transport heat from the dayside to the nightside, preventing the dayside from becoming as scorching as predicted. Bright clouds made of vaporized rock or silicates may also reflect some of the star’s light.
The planet’s unusually low density adds another piece to the puzzle. TOI-561 b seems lighter than a rocky planet with an Earth-like composition should be. While this could partly be explained by differences in its internal makeup, researchers believe a thick atmosphere that makes the planet appear larger is likely playing a major role.
TOI-561 b is especially intriguing because it orbits a very old, iron-poor star—about twice the age of the Sun—in a region of the Milky Way known as the thick disk. This suggests the planet formed in a very different chemical environment from Earth and may resemble worlds that formed when the universe was much younger.
Researchers now think the planet exists in a delicate balance. Gases escape from the molten surface into the atmosphere, while the magma ocean pulls some of them back into the interior. This constant exchange could allow the atmosphere to survive despite the intense heat. In essence, TOI-561 b may be a “wet lava world,” rich in volatile materials unlike anything in our solar system.
The team observed the system continuously for more than 37 hours as the planet completed nearly four orbits. They are now analyzing the full data set to map temperatures across the entire planet and better understand what its atmosphere is made of.
These results open a new window on rocky worlds and suggest that even planets forged in extreme heat can be far more complex than once imagined.
