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Webb Telescope spots “impossible” atmosphere on ancient super Earth

A scorching “lava world” once thought barren may actually be wrapped in a thick, mysterious atmosphere.

Date:

March 22, 2026

Source:

Carnegie Institution for Science

Summary:

Astronomers have uncovered surprising evidence of a thick atmosphere surrounding TOI-561 b, a scorching, fast-orbiting rocky planet once thought too extreme to hold onto any gas. Using NASA’s James Webb Space Telescope, researchers found the planet is far cooler than expected for a bare rock, hinting at a heat-distributing atmosphere above a churning magma ocean. This strange world—where a year lasts just over 10 hours and one side is locked in eternal daylight—may even be rich in volatile materials, behaving like a “wet lava ball.”

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A super-hot rocky planet orbiting its star in just 10 hours appears to have a surprisingly thick atmosphere, despite conditions that should strip it away. Scientists think it may be a volatile-rich “wet lava world” with a magma ocean feeding and recycling its gases. Credit: AI/ScienceDaily.com

A team of astronomers led by Carnegie has uncovered the clearest evidence yet that a rocky planet outside our Solar System has an atmosphere. Using NASA's James Webb Space Telescope (JWST), the researchers identified signs of gas surrounding an unusual target: an ancient, extremely hot super Earth that likely has a surface covered by molten rock. The findings were published in The Astrophysical Journal Letters.

The planet, known as TOI-561 b, has about twice the mass of Earth but is dramatically different in almost every other way. It orbits extremely close to its star, at a distance just one fortieth that of Mercury from the Sun. Even though its star is slightly smaller and cooler than our Sun, the planet's tight orbit means it completes a full year in only 10.56 hours. One side constantly faces the star, leaving it locked in permanent daylight.

"Based on what we know about other systems, astronomers would have predicted that a planet like this is too small and hot to retain its own atmosphere for long after formation," explained Carnegie Science Postdoctoral Fellow Nicole Wallack, the paper's second author. "But our observations suggest it is surrounded by a relatively thick blanket of gas, upending conventional wisdom about ultra-short-period planets."

In our Solar System, planets that are both small and intensely heated tend to lose their original gas envelopes early in their history. However, TOI-561 b orbits a much older star than the Sun, and despite its harsh conditions, it appears to have held onto its atmosphere.

Low Density Clues Point to an Unusual Composition

The possible presence of an atmosphere may help explain another puzzle: the planet's lower than expected density.

"It's not what we call a super-puff -- or 'cotton candy' planet -- but it is less dense than you would expect if it had an Earth-like composition," said Carnegie Science astronomer Johanna Teske, the study's lead author.

Before analyzing the new data, the team considered whether the planet's structure alone could account for this. One idea was that TOI-561 b might have a smaller iron core and a mantle made of lighter rock compared to Earth.

Teske added that this idea fits with the planet's origins: "TOI-561 b is distinct among ultra-short period planets in that it orbits a very old -- twice as old as the Sun -- iron-poor star in a region of the Milky Way known as the thick disk. It must have formed in a very different chemical environment from the planets in our own Solar System."

This suggests the planet could resemble worlds that formed when the universe was much younger. Still, composition alone does not fully explain the observations.

JWST Temperature Data Reveals Hidden Atmosphere

The research team also proposed that a thick atmosphere could make the planet appear larger and therefore less dense. To investigate this, they used JWST's Near-Infrared Spectrograph (NIRSpec) to measure the temperature of the planet's dayside by observing its brightness in near infrared light. This method tracks how the system's light changes when the planet moves behind its star, a technique also used to study planets in the TRAPPIST-1 system.

If TOI-561 b had no atmosphere, its dayside temperature should reach nearly 4,900 degrees Fahrenheit (2,700 degrees Celsius). Instead, the measurements showed a lower temperature of about 3,200 degrees Fahrenheit (1,800 degrees Celsius). While still extremely hot, this difference strongly suggests that heat is being redistributed across the planet.

Winds, Clouds, and a Volatile Rich Atmosphere

To account for the cooler temperature, scientists explored several possibilities. A molten surface ocean could move some heat, but without an atmosphere, the nightside would likely remain solid, limiting heat transfer. A thin lay