The lava planet TOI-561 b appears to retain a reflective atmosphere despite intense stellar radiation, according to research highlighted by the University of Waterloo on October 26 and in University of Birmingham material published by ScienceDaily on October 27. The observations strengthen earlier evidence for an atmosphere; they do not establish its chemical composition.
Lisa Dang of Waterloo and collaborators monitored the planet with the James Webb Space Telescope for 37 hours, covering nearly four orbits. Their study appears in The Astronomical Journal, with a preprint available since August. The team tracked changes in brightness and thermal emission around the orbit, a technique called a phase curve, to examine how the planet distributes energy.
Earlier observations showed a dayside cooler than expected for bare, dark rock. Heat transport to the permanently dark hemisphere could explain part of that difference, but the new nightside measurements did not account for all of it. Waterloo reports that the planet must reflect roughly three-quarters of incoming starlight, comparable to Venus, while also moving heat around its surface.
The researchers compared the observations with climate simulations. Their paper identifies silicon dioxide and magnesium silicate clouds as possible explanations for the high reflectivity, with suitable conditions near the boundary between day and night on the illuminated side. These are model-based possibilities, rather than a direct identification of cloud chemistry. The findings challenge expectations that intense irradiation strips such rocky worlds of substantial atmospheres.
The atmosphere's composition and survival remain unresolved. Waterloo describes carbon dioxide and sulfur dioxide as possibilities, and gases escaping from the molten interior could replenish the atmosphere. Dang said observations at longer wavelengths with Webb could help distinguish those scenarios. The next scientific task is to test the proposed chemistry and explain how this extreme planet has maintained its gaseous envelope.
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