NASA's James Webb Telescope detects thick atmosphere around scorching lava world

Despite this extreme environment, TOI-561 b has an unusually low density. That feature puzzled astronomers for years. “It’s less dense than expected for an Earth-like composition,” said Johanna Teske of Carnegie Science, the study’s lead author.

This artist’s concept shows what the hot super-Earth exoplanet TOI-561 b and its star could look like based on observations from NASA’s James Webb Space Telescope and other observatories. Webb data suggests that the planet is surrounded by a thick atmosphere above a magma ocean. (Image: NASA, ESA, CSA, Ralf Crawford (STScI))

What the Webb Data Reveal

Researchers tested whether an atmosphere could explain the planet’s properties. Using Webb’s Near-Infrared Spectrograph, they measured the planet’s dayside temperature. The method tracks brightness changes as the planet passes behind its star.

If the planet lacked an atmosphere, temperatures should reach about 4,900 degrees Fahrenheit. Instead, Webb measured roughly 3,200 degrees Fahrenheit. The cooler reading suggests heat redistribution across the planet.

Scientists say only a thick atmosphere can explain this effect. “We really need a volatile-rich atmosphere,” said co-author Anjali Piette from the University of Birmingham. Strong winds could move heat to the nightside. Gases may also absorb infrared radiation.

An emission spectrum recorded by NASA’s James Webb Space Telescope in May 2024 displays the intensity of near-infrared wavelengths emitted by exoplanet TOI-561 b. Comparisons with models indicate the planet is enveloped by a volatile-rich atmosphere. Illustration. (Image: NASA, ESA, CSA, Ralf Crawford (STScI); Science: Johanna Teske (Carnegie Science Earth and Planets Laboratory), Anjali Piette (University of Birmingham), Tim Lichtenberg (Groningen), Nicole Wallack (Carnegie Science Earth and Planets Laboratory))

What This Means for Planetary Science

The discovery challenges long-held assumptions about small planets near stars. Such worlds were thought unable to retain atmospheres after billions of radiation exposure. TOI-561 b suggests otherwise.

The planet may have formed in a different chemical environment. It orbits an iron-poor star twice the Sun’s age. That star lies within the Milky Way’s thick disk. Scientists say the planet could reflect early universe conditions.

Researchers propose an equilibrium between magma and atmosphere. Gases escape into the atmosphere, then dissolve back into molten rock. “It’s really like a wet lava ball,” said co-author Tim Lichtenberg.

The observations came from Webb’s General Observers Program 3860. The telescope monitored the system for over 37 hours. Scientists are now analysing full data to map global temperatures and identify atmospheric composition.

“What’s exciting is how many new questions this raises,” Teske said.