Ancient Super‑Earth Shows Signs of a Surprising Atmosphere * Science and Technology Times

Astronomers using the James Webb Space Telescope have detected evidence of an atmosphere around the ultra‑hot super‑Earth TOI‑561 b.
The planet, once assumed too small and scorched to hold onto gas, appears cooler than expected on its dayside.
New findings challenge long‑held assumptions about rocky exoplanets orbiting extremely close to their stars.

A Rocky World That Shouldn’t Have an Atmosphere

A research team led by Carnegie scientists has identified the clearest evidence so far that a rocky exoplanet can retain an atmosphere under extreme conditions. Their target, TOI‑561 b, is a super‑Earth roughly twice the mass of our planet but vastly different in structure and environment. It orbits its star at a distance only one‑fortieth that of Mercury from the Sun, completing a full orbit in just 10.56 hours. One hemisphere remains locked in perpetual daylight due to tidal locking.

Astronomers have long believed that planets this small and hot should lose their atmospheres early in their history. Intense radiation and stellar winds typically strip away gases, leaving behind bare rock. TOI‑561 b, however, orbits a star that is twice as old as the Sun, making its apparent atmospheric persistence even more unexpected. The discovery challenges established models of atmospheric survival on ultra‑short‑period planets.

Nicole Wallack, a Carnegie Science postdoctoral fellow and co‑author of the study, noted that the observations contradict predictions based on similar systems. She explained that the planet appears to be wrapped in a relatively thick layer of gas despite its extreme environment. This finding suggests that some rocky planets may be more resilient than previously thought. It also raises new questions about how such atmospheres form and evolve.

Low Density Hints at an Unusual Composition

The planet’s density has puzzled researchers since its discovery. Measurements show that TOI‑561 b is less dense than expected for a rocky world with an Earth‑like composition. This discrepancy prompted scientists to explore whether its internal structure might differ significantly from Earth’s. One hypothesis suggested a smaller iron core and a mantle composed of lighter rock.

Johanna Teske, the study’s lead author, pointed out that the planet’s formation environment may explain some of these differences. TOI‑561 b orbits an iron‑poor star located in the Milky Way’s thick disk, a region associated with older stellar populations. This implies that the planet formed under chemical conditions unlike those of the early Solar System. Even so, composition alone could not fully account for the observed density.

The possibility of an atmosphere offered a compelling alternative explanation. A thick gaseous layer would make the planet appear larger and therefore less dense. This idea motivated the team to examine the planet’s temperature using JWST’s Near‑Infrared Spectrograph.

JWST Temperature Measurements Reveal Heat Redistribution

To test the atmospheric hypothesis, researchers measured the planet’s dayside temperature by observing how its infrared brightness changed when it passed behind its star. If TOI‑561 b lacked an atmosphere, its dayside should reach nearly 4,900 degrees Fahrenheit (2,700 degrees Celsius). Instead, JWST detected a significantly cooler temperature of about 3,200 degrees Fahrenheit (1,800 degrees Celsius). This difference strongly suggests that heat is being redistributed across the planet.

A molten surface alone cannot efficiently move heat from the dayside to the nightside. Without an atmosphere, the nightside would likely remain solid and much cooler. A thin layer of vaporized rock could exist, but it would not provide enough cooling to match the observations. These limitations point toward a substantial atmosphere capable of transporting heat.

Co‑author Anjali Piette explained that a volatile‑rich atmosphere could produce the observed temperature patterns. Winds would move heat across the surface, while gases such as water vapor could absorb infrared light before it escapes into space. Bright silicate clouds might also reflect starlight, contributing to the cooling effect. Together, these factors support the presence of a thick atmospheric layer.

A Dynamic Balance Between Magma and Atmosphere

The existence of an atmosphere raises a fundamental question: how does a planet this hot retain gas at all? Some atmospheric material is likely escaping into space, but the rate appears slower than expected. One explanation involves a balance between the planet’s molten interior and its atmosphere. Gases may continuously cycle between the magma ocean and the surrounding air.

Tim Lichtenberg, a co‑author from the University of Groningen, described the planet as a “wet lava ball” with a volatile‑rich composition. He suggested that the magma ocean may absorb gases at the same time that new material escapes from the interior. This dynamic equilibrium could help sustain the atmosphere over long periods. The process may resemble early stages of planetary evolution in the young universe.

The findings open new avenues for studying how rocky planets evolve under extreme conditions. They also highlight the value of JWST’s infrared capabilities for probing the atmospheres of small, hot exoplanets. Researchers plan to analyze the full dataset to map temperature variations across the entire planet. These results may reveal more about the composition and behavior of TOI‑561 b’s atmosphere.

JWST Continues to Transform Exoplanet Science

The observations were conducted as part of JWST’s General Observers Program 3860, which monitored the system for more than 37 hours. Carnegie researchers have played a significant role in JWST science since the telescope’s development, contributing to studies of exoplanets, galaxies, and cosmic evolution. The team expects additional insights as they continue analyzing the data. Their work underscores how JWST is reshaping our understanding of planetary atmospheres.

Michael Walter, director of Carnegie’s Earth and Planets Laboratory, emphasized that these findings build on decades of research into planetary formation and dynamics. He noted that more discoveries are likely as JWST continues to observe diverse exoplanet systems. The study of TOI‑561 b demonstrates how even extreme worlds can challenge assumptions and reveal new physical processes. Future observations may uncover similar atmospheric signatures on other ultra‑hot rocky planets.