Astronomers using the James Webb Space Telescope have discovered that TOI-561 b, a rocky exoplanet located approximately 280 light-years from Earth, reflects approximately 75 percent of the starlight reaching it. This unexpected reflectivity points to a substantial, heat-redistributing atmosphere protected by a layer of silicate clouds acting as a giant sunscreen.
Observations of TOI-561 b via the James Webb Space Telescope
The international team monitored the rocky exoplanet over 37 hours, observing nearly four complete orbits around its host star. Because the same side of TOI-561 b always faces its star, researchers could examine the permanently dark nightside for the first time. The measurements showed that this hemisphere was not warm enough to account for all the missing thermal energy. Instead, the data revealed that the planet reflects approximately 75 percent of incoming starlight, a remarkably high proportion comparable to Venus.
Computer climate models suggest that clouds containing silicate minerals—specifically silicon dioxide (SiO2) and magnesium silicate (MgSiO3)—form over the dayside. These clouds prevent the surface from reaching the extreme temperatures typically expected on an exposed, heavily irradiated rocky planet. Furthermore, the observations indicate that the atmosphere actively moves heat from the permanently illuminated dayside toward the nightside.
The Mystery of a Surviving Atmosphere on a Scorched Planet
Dr. Anjali Piette, Assistant Professor in Astronomy at the University of Birmingham, noted that current theoretical models would expect a heavily irradiated rocky world like TOI-561 b to have lost its atmosphere billions of years ago. Instead, the planet maintains a significant atmosphere today. Scientists have not yet determined the exact chemical composition of this atmosphere. Candidates include a thick layer of carbon dioxide similar to the atmosphere of Venus under much hotter conditions, or an atmosphere dominated by sulfur dioxide, a gas released by volcanic activity on Jupiter’s moon Io.
Researchers are investigating whether the planet started with an unusually large supply of gases or if the ocean of molten rock covering its surface functions as a planet-wide volcano, constantly feeding new material into the atmosphere to replace what escapes.
Future Observations to Determine Atmospheric Composition
Professor Lisa Dang, who led the project at the University of Waterloo in Ontario, Canada, explained that measuring the planet’s phase curve across its orbit revealed both the high light reflectivity and the efficient heat redistribution. The next phase of research will focus on observing TOI-561 b at longer wavelengths using the James Webb Space Telescope. These upcoming observations aim to clarify the chemical makeup of the atmosphere and resolve how a planet subjected to such intense radiation has held onto its atmosphere over billions of years.
