NASA’s James Webb Space Telescope has found the most compelling evidence so far that a small, rocky exoplanet beyond our solar system possesses an atmosphere, even with its tight orbit around its star. The exoplanet, designated TOI-561 b, measures less than 1.5 times the diameter of Earth and orbits its star in under 11 hours. This closeness—fewer than 1 million miles away—results in one side of the planet always being exposed to the star, likely leading to a hemisphere hot enough to liquefy rock, forming a lava ocean.

Scientists were taken aback by the planet’s low density. “What truly distinguishes this planet is its peculiarly low density,” stated Johanna Teske, the study’s lead author. “It isn’t a super-puff, but it is less dense than one would anticipate if it had a composition like Earth’s.”

The existence of an atmosphere on TOI-561 b implies that even rocky exoplanets in extreme environments can sustain air, providing fresh insights for researchers looking for habitable planets in other parts of the galaxy.

At first, scientists contemplated whether TOI-561 b, situated 280 light-years away, developed from atypical materials. The planet’s host star is a G-type star similar to the sun but is quite old and contains minimal iron, which might indicate a chemistry akin to that of worlds from the early universe. Nonetheless, this factor alone could not account for the observational data.

The research team then investigated the idea of a dense atmosphere. Webb gauged the planet’s thermal radiation by monitoring infrared light variations as the planet transited behind its star, enabling scientists to assess the surface temperature.

If the planet were a naked rock devoid of an atmosphere, its sunlit side would reach approximately 4,900 degrees Fahrenheit. Instead, Webb detected a cooler temperature around 3,200 degrees. The results are documented in The Astrophysical Journal Letters.

“We genuinely require a thick, volatile-rich atmosphere to clarify all the observations,” said coauthor Anjali Piette. An atmosphere could cool the planet by generating winds that transport heat to the dark side, and elements like water vapor might prevent heat from escaping. Luminous clouds could also reflect starlight.

The team intends to keep investigating the planet to chart surface temperatures and decode its atmospheric makeup. Researchers are uncertain how a small planet preserves its atmosphere amid intense radiation, but some theorize that gases could cycle between the lava ocean and the atmosphere.

“This planet has to be significantly more volatile-rich than Earth,” remarked coauthor Tim Lichtenberg. “It’s truly like a wet lava ball.”