Astronomers using the James Webb Space Telescope (JWST) have detected a substantial atmosphere on the lava-covered exoplanet TOI-561 b. Located approximately 280 light-years from Earth, the rocky world remains unexpectedly cool for its proximity to its star, suggesting that a reflective layer of silicate clouds acts as a giant sunscreen
to protect the surface.
Reflective Clouds on TOI-561 b
Monitoring the planet for 37 hours, an international research team observed nearly four complete orbits. By utilizing a phase curve—a technique measuring how brightness and heat shift throughout an orbit—scientists were able to examine the planet’s nightside for the first time. While researchers previously assumed such a heavily irradiated rocky world would have lost its atmosphere billions of years ago, the data indicates the presence of a persistent, global gas envelope. This atmosphere appears to be a critical factor in the planet’s unexpected thermal profile, as it helps redistribute heat from the permanently illuminated dayside toward the nightside. The study, titled A Highly Reflective Atmosphere on the Lava World TOI-561 b Revealed by JWST/NIRSpec Phase Curve, was published on September 29, 2026, in The Astronomical Journal.
Computer simulations conducted by the team suggest this cooling effect is driven by clouds containing silicate minerals, specifically silicon dioxide (SiO2) and magnesium silicate (MgSiO3). These clouds form over the dayside, shielding the molten surface from the star’s intense radiation before it can be absorbed.
Molten Rock Surface May Feed the Atmosphere
The persistence of an atmosphere on a planet with a surface hot enough to melt rock presents a significant challenge to current climate models. Researchers are now investigating whether the ocean of molten rock covering the surface acts as a planet-wide volcano
that is constantly feeding its atmosphere. The team also determined that the nightside is not warm enough to account for all the missing heat, strengthening the argument that reflection, rather than just heat circulation, is responsible for the planet’s subdued dayside temperatures. The team’s work builds on earlier evidence from Professor Lisa Dang, Dr. Anjali Piette, and their collaborators regarding the planet’s thick, replenished atmosphere.
Lava planet TOI-561 b reflects roughly 75% of incoming starlight, pointing to an atmosphere that could contain reflective clouds of silicate minerals. @AAS_Publishing https://t.co/dGseEJtMhf
Our discovery challenges current theories. We would expect a heavily irradiated rocky planet like TOI-561 b to have lost its atmosphere billions of years ago. Instead, the evidence suggests it still has a significant atmosphere today.
The chemical composition of this air remains an open question. The team is currently weighing two primary theories: a dense carbon dioxide atmosphere similar to a hotter version of Venus, or one dominated by sulfur dioxide, a gas released by volcanic activity on Jupiter’s moon Io.
Future Observations with the James Webb Space Telescope
To differentiate between these chemical possibilities, the team plans to conduct further observations at longer wavelengths using Webb. Professor Lisa Dang, who led the project at the University of Waterloo in Ontario, Canada, noted that this next phase of study is essential to understanding how such an extreme environment can maintain its gaseous shield over geological timescales.
The next big question we will seek to answer is whether TOI-561 b’s atmosphere resembles Venus or an extreme version of Io. Observing the planet at longer wavelengths with JWST could give us insights and help explain how a planet this hot has held on to an atmosphere for billions of years.
While TOI-561 b is far from being hospitable to life, the ability to analyze its reflective properties and heat redistribution provides a new benchmark for studying the evolution of lava worlds orbiting close to their host stars. The research confirms that carrying heat away from the dayside cannot account for all of the planet’s apparent cooling. Other contributors to the project include Samuel Boucher, Alex McGinty, Johanna K. Teske, Raymond Pierre Humbert, Tim Lichtenberg, Mykhaylo Plotnykov, Emma Postolec, and Daniel Huber.