Astronomers finally find an atmosphere around a rocky exoplanet

From Io’s volcanoes to Enceladus’s geysers, our Solar System is a study in contrasts. The exoplanet realm is just as rich—and scientists are hunting for signs of life or, at least, clues to how life might emerge in the Universe. The JWST has just added a fresh chapter to that story.

The year 2025 is drawing to a close. A century ago, Werner Heisenberg, followed by Max Born and Pascual Jordan, developed matrix mechanics, while Erwin Schrödinger introduced his famous equation—first reshaping de Broglie’s matter-wave theory, then quantum mechanics itself with a paper published in January 1926.

But 2025 wasn’t only the International Year of Quantum Science and Technology; it also marked 30 years since Michel Mayor and Didier Queloz discovered the first exoplanet around a main-sequence star—the same stellar class as our Sun, which will eventually leave the sequence to become a red giant and later a white dwarf.

The surprise back then was the nature of that planet: a hot Jupiter, a gas giant likely formed far from its star—often a red dwarf, the most common stars in the Milky Way—that later migrated inward and now bakes at temperatures topping a thousand degrees.

Soon after came our first glimpses of giant-planet atmospheres—think Osiris—and then the early finds of rocky worlds, many super Earths, and eventually Earth-sized planets in the famed, if sometimes overhyped, habitable zone.

By late December 2025, more than 7,910 exoplanets were on the books—check the Extrasolar Planets Encyclopedia founded by Paris Observatory astronomer Jean Schneider. For a quick primer on how we study them, the CEA’s web series offers accessible guides.

Exoplanet detection methods have diversified considerably since the 1990s. They can be classified into two main categories: direct methods and indirect methods. The three principal methods are the direct imaging method, the indirect transit method, and the indirect radial velocity method. © CEA Research

Planets with oceans of magma

The biosignature quest zeroes in on rocky exoplanets that keep an atmosphere. To study one, you want a nearby system with planetary transits. That’s exactly why NASA launched TESS, successor to Kepler.

TESS has flagged numerous TOIs—TESS Objects of Interest—ripe for follow-up, especially with JWST’s infrared spectroscopy via instruments like NIRSpec.

Among them, TOI-561 b is having its moment, highlighted in several releases, including from the Trottier Institute for Research on Exoplanets at the University of Montreal.

A study in The Astrophysical Journal Letters, also available on arXiv, reports the strongest evidence yet for an atmosphere on a rocky world beyond our Solar System.

Specifically, JWST data point to a global magma ocean on TOI-561 b, akin to early Earth’s Hadean past—and likely the Moon’s—shrouded by a thick atmosphere.

How did researchers reach that conclusion?

First, despite orbiting a Sun-like G-type star and measuring about 1.4 Earth radii, TOI-561 b hugs its star at just 1.6 million kilometers—roughly one-fortieth of Mercury’s distance from the Sun.

A rocky exoplanet with exotic composition?

At that range, tidal forces almost certainly lock the planet in synchronous rotation, always showing the same face—like our Moon. The permanent dayside should soar well above typical rock-melting temperatures, consistent with a global magma ocean.

So far, so familiar for ultra-hot rocky worlds. But the team found an unexpectedly low bulk density, tightening constraints on the planet’s interior.

The likely structure: a relatively small iron core wrapped in a mantle of rock less dense than Earth’s.

That fits the system’s history. TOI-561 is roughly twice the Sun’s age, meaning the planet formed when the Milky Way was poorer in heavy elements like iron, magnesium, and aluminum. Fewer heavy elements in the birth cloud yield a less-dense rocky makeup.

Over cosmic time, massive stars seed the interstellar medium with heavy elements through supernovae, enriching the galaxy. Ten billion years ago, that enrichment was less advanced—hence TOI-561 b’s lower heavy-element content compared with Solar System planets.

Even so, the low density needs another ingredient: a thick atmosphere that inflates the planet’s apparent radius.

How to test that idea?

An atmosphere revealed by secondary planetary transits?

Astronomers watched TOI-561 b slip behind its star during secondary eclipses, then subtracted starlight to estimate the dayside temperature.

If an atmosphere exists, winds should redistribute heat from day to night, lowering the dayside temperature relative to a bare-rock case.

Indeed, instead of the predicted 2,700 degrees Celsius without an atmosphere, they measured about 1,800 degrees Celsius.

Co-author Anjali Piette (University of Birmingham) explains: strong winds in a volatile-rich atmosphere would ferry heat to the nightside, while gases like water vapor absorb near-infrared wavelengths emitted by the surface, making the planet appear cooler. Bright silicate clouds could also reflect starlight and further cool the atmosphere.

Another puzzle: so close to its star, the planet’s atmosphere should have boiled away. Why hasn’t it?

Co-author Tim Lichtenberg (University of Groningen) suggests a dynamic balance between magma ocean and atmosphere: as gases escape to replenish the air, the molten mantle reabsorbs them. In short, a volatile-rich world—a “wet lava ball.”

Did you know

In May 2024, JWST’s NIRSpec captured an emission spectrum from 3 to 5 microns for ultra-hot super-Earth TOI-561 b. Comparing the data with models shows the planet is no bare rock but is enveloped in a volatile-rich atmosphere.

The measurements track brightness changes before, during, and after four consecutive secondary eclipses across nearly four orbits. Although the planet can’t be resolved from its star, subtracting the star-only light from the combined light reveals the planet’s contribution—mostly from its sunlit hemisphere, consistent with synchronous rotation.

Model spectra indicate that a bare surface or a thin water-vapor layer would appear much brighter than observed. The data instead align with an atmosphere rich in volatiles such as water, oxygen, and carbon dioxide.

A thick atmosphere absorbs some near-infrared emission from the surface, dimming the signal, and wind-driven circulation redistributes heat—cooler dayside, warmer nightside.

JWST watched the system for over 37 hours to secure these observations.

Credit: NASA, ESA, CSA, Ralf Crawford (STScI). Science: J. Teske, A. Piette, T. Lichtenberg, N. Wallack.