The universe continues to unveil its mysteries, especially through the groundbreaking observations of the James Webb Space Telescope (JWST). In a pivotal announcement, scientists have now detected the strongest evidence yet for an atmosphere on the molten rocky exoplanet TOI-561 b. This discovery is not only a testament to Webb’s unparalleled capabilities but also challenges long-held theories about planetary survival near scorching stars.
Since its science operations began in mid-2022, the JWST has revolutionized our understanding of exoplanet atmospheres. It provided the first clear evidence of carbon dioxide on WASP-39b and atmospheric water vapor on WASP-96b. Now, new data reveals that the ultra-hot super-Earth TOI-561 b, a world significantly hotter than our own, surprisingly harbors a thick gaseous blanket. This finding suggests a dynamic interplay between a vast magma ocean and the atmosphere above it, marking a fascinating new chapter in exoplanet research.
Decoding TOI-561 b: An Ultra-Hot Super-Earth
TOI-561 b is an intriguing exoplanet, roughly 1.4 times Earth’s radius, located approximately 275 light-years away. It orbits a Sun-like star at an incredibly close distance, completing a full revolution in less than 11 hours. This makes it a rare example of an “ultra-short period” (USP) exoplanet. Its extreme proximity means it endures intense stellar radiation and is likely tidally locked, with one side perpetually facing its star.
Such extreme conditions typically lead scientists to expect these planets to be barren, airless worlds. Dayside temperatures on TOI-561 b easily exceed the melting point of rock, indicating a surface covered by a global magma ocean. Yet, the JWST’s Near-Infrared Spectrometer (NIRSpec) observations suggest otherwise, pointing to a substantial atmosphere on exoplanet TOI-561 b. This unexpected finding directly questions the prevailing scientific theory that small planets orbiting so closely to their stars cannot retain atmospheres.
A Planet Forged in the Early Universe
Measurements of TOI-561 b’s size and mass have revealed an unusually low density for a purely rocky body. This suggests a composition that might include a relatively small iron core and a mantle made of rock less dense than Earth’s. Lead researcher Johanna Teske, from the Carnegie Institution for Science, highlighted the planet’s unique origin story. TOI-561 b orbits an exceptionally old star, estimated to be around 10.5 billion years old, located in the Milky Way’s thick disk.
This ancient stellar system implies that TOI-561 b must have formed in a profoundly different chemical environment compared to our own solar system. Its composition could offer insights into planets that came into existence when the universe was still relatively young. This deep historical context adds another layer of intrigue to the discovery of its enduring atmosphere on the molten rocky exoplanet.
Webb’s Breakthrough: Probing a Magma World’s Air
To investigate the possibility of an atmosphere, the research team employed Webb’s NIRSpec instrument. In May 2024, the telescope continuously observed the TOI-561 b system for over 37 hours. This extended observation period allowed them to capture nearly four complete orbits of the exoplanet. The team specifically focused on “secondary eclipses”—moments when TOI-561 b passed behind its host star.
By precisely measuring the minute decrease in the system’s total brightness during these eclipses, scientists could isolate and determine the planet’s dayside temperature. This advanced technique, akin to emission spectroscopy, effectively measures the infrared light emitted by the planet itself. Without an atmosphere to redistribute heat, the team predicted an extreme dayside temperature of approximately 2,700 °C (4,900 °F).
The Cooling Effect of an Atmosphere
The NIRSpec observations, however, delivered a startling revelation: TOI-561 b’s dayside temperature was significantly cooler, measured at approximately 1,800 °C (3,200 °F). This substantial 900 °C (1,700 °F) temperature difference provided compelling evidence. As co-author Dr. Anjali Piette from the University of Birmingham explained, “We really need a thick, volatile-rich atmosphere to explain all the observations.”
Such an atmosphere on exoplanet TOI-561 b would feature strong winds capable of transporting heat from the scorching dayside to the cooler nightside. This heat redistribution would effectively cool the dayside. Additionally, gases like water vapor within the atmosphere would absorb certain wavelengths of near-infrared light emitted by the surface. This absorption would lead the telescope to detect less light, making the planet appear colder than its molten surface. The presence of bright silicate clouds, reflecting starlight, could also contribute to this observed cooling effect.
A “Wet Lava Ball”: A New Model for Planetary Evolution
A central question arising from this discovery is how a small, tidally-locked planet, exposed to such intense stellar radiation, could possibly maintain a dense atmosphere. Co-author Tim Lichtenberg from the University of Groningen proposed a fascinating solution: a dynamic equilibrium between the planet’s magma ocean and its atmosphere.
In this model, gases are continuously released from the planet’s molten interior, feeding the atmosphere. Simultaneously, the vast magma ocean reabsorbs these gases back into the planet’s interior. This constant cycling suggests that TOI-561 b must be “much, much more volatile-rich than Earth,” as Lichtenberg vividly described, calling it “a wet lava ball.” This novel concept has profound implications for understanding how extremely hot rocky planets evolve and retain their atmospheres.
This groundbreaking research provides the first results from Webb’s General Observers (GO) Program 3860, part of its Cycle 2 initiatives. The team is now meticulously analyzing the complete dataset to determine temperatures across both sides of the planet and to further characterize the precise composition of this unique atmosphere on the molten rocky exoplanet. Future studies will undoubtedly continue to push the boundaries of our understanding of these distant, extreme worlds.
Frequently Asked Questions
What makes the TOI-561 b atmosphere discovery so significant?
The discovery of a thick atmosphere on TOI-561 b is highly significant because it challenges established scientific theories. Previously, it was thought that small, rocky planets orbiting extremely close to their stars would lose their atmospheres due to intense stellar radiation. TOI-561 b, an ultra-hot super-Earth covered by a magma ocean, demonstrates that a dynamic equilibrium between a molten interior and its atmosphere can allow a planet to retain a gaseous envelope, offering new insights into planetary formation and evolution in extreme environments.
How did the James Webb Space Telescope confirm an atmosphere on TOI-561 b?
The James Webb Space Telescope (JWST) confirmed the atmosphere using its Near-Infrared Spectrometer (NIRSpec) and a technique involving “secondary eclipses.” Scientists observed TOI-561 b passing behind its star, measuring the decrease in infrared light. By comparing the observed dayside temperature (1,800 °C) with the predicted temperature if no atmosphere existed (2,700 °C), they found a significant cooling effect. This 900 °C discrepancy could only be explained by a thick, volatile-rich atmosphere redistributing heat and absorbing light.
What does the discovery of an atmosphere on a “wet lava ball” like TOI-561 b mean for the search for life?
While TOI-561 b’s extremely hot, molten surface makes it an unlikely candidate for life as we know it, this discovery profoundly impacts the broader search for life. It expands our understanding of the diverse conditions under which planets can form and retain atmospheres, even in hostile environments. This knowledge helps scientists refine models of planetary habitability and evolution, informing future searches for potentially life-supporting atmospheres on more temperate exoplanets. It highlights that the universe is far more complex and surprising than previously imagined.
