James Webb reports reflective atmosphere on lava world
The ultra‑hot planet TOI‑561 b, long thought to be bare rock, may hold a thick, reflective atmosphere fed by its molten surface.
29 Oct 2026 0 reads Compiled with AI
The James Webb Space Telescope has detected a surprising atmosphere around TOI‑561 b, a scorching exoplanet about 280 light‑years from Earth. The planet orbits so close to its star that a year lasts less than 11 hours. It appears to be wrapped in a thick, highly reflective atmosphere that bounces back roughly 75% of the starlight it receives.
Planet’s extreme environment
TOI‑561 b is about 1.4 times wider than Earth and hugs its Sun‑like star at less than a million miles away. It is almost certainly tidally locked, with a permanent dayside. A bare, dark rock in that orbit should reach about 4,900 °F (2,700 °C). JWST measured a dayside closer to 3,200 °F (1,800 °C), leaving a lot of heat unaccounted for.
The team, led by Lisa Dang at the University of Waterloo, used JWST’s NIRSpec instrument to observe the planet for 37 hours as it completed nearly four orbits. The method, called a phase curve, tracks brightness and heat as the planet moves around its star. Dang said: 'We measured how the planet’s brightness and heat changed throughout its orbit…' The results suggest much of the missing energy is either carried to the nightside or reflected back into space, pointing to an atmosphere.
How the clouds reflect starlight
Computer models suggest that clouds of silicate minerals, including silicon dioxide and magnesium silicate, may form high over the dayside. If so, they could act as a planet‑sized sunscreen, reflecting starlight before it reaches the surface.
The composition of the remaining atmosphere is still unclear. It could be dominated by carbon dioxide, similar to Venus, or by sulfur dioxide, the gas released by volcanic activity on Jupiter’s moon Io. Dr. Anjali Piette, assistant professor in astronomy at the University of Birmingham, said: '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.' Observations at longer wavelengths could help reveal the gas mix and explain how the planet has kept its atmosphere for billions of years.