Key facts
- TOI-561 b is a rocky lava planet once considered too extreme to retain an atmosphere, but it appears wrapped in an atmosphere with reflective clouds of vaporized silicate minerals related to quartz and sand.
- Lisa Dang, a physics and astronomy professor at the University of Waterloo, led JWST observations of TOI-561 b lasting 37 hours and capturing nearly four complete orbits around its star.
- TOI-561 b reflects about three-quarters of incoming starlight, a reflectivity similar to Venus, because its night side is too cool to account for the missing heat.
- Computer climate models suggest that dayside clouds built from silicate minerals such as silicon dioxide and magnesium silicate could reflect starlight and cool the planet like sunscreen.
University of Waterloo astronomer Lisa Dang led an international team, including University of Birmingham astronomer Anjali Piette, in 37 hours of James Webb Space Telescope observations of TOI-561 b, spanning nearly four trips around its star, and found the rocky lava planet about 280 light-years from Earth has an atmosphere with reflective clouds made from vaporized silicate minerals related to quartz and sand, researchers reported Oct. 26, 2026.
Dang explained that the team measured brightness and heat changes throughout the planet’s orbit. The team’s measurements show the planet reflects substantial starlight and that warmth shifts around the world rather than remaining only on the sunlit side, results that together point to an atmosphere. TOI-561 b reflects about three-quarters of incoming starlight, matching Venus’s reflectivity, and its dayside runs far cooler than expected for bare rock orbiting so near a star. The atmosphere shifts heat toward the dark side, which brings down dayside temperatures.
The team’s computer climate models point to clouds on the dayside made from silicon dioxide and magnesium silicate, minerals related to quartz and sand. The team compared observations with a computer climate simulation, which points to silicate clouds forming on the dayside. General circulation model cloud maps put plausible silicon dioxide and magnesium silicate condensates near the terminator on the dayside, the dividing line between day and night. The clouds reflect starlight and cool the planet like sunscreen while permitting gases from the interior to keep entering the atmosphere, supplying the measured reflectivity.
Reflecting incoming starlight and lowering temperatures, the clouds could let the planet hold onto an atmosphere that strong stellar radiation would otherwise take away. Past research from Dang and collaborators suggested the planet has a thick atmosphere, with gases from its molten interior probably feeding it. A molten-rock ocean covers the planet and could act like a planet-wide volcano, steadily sending gases into the atmosphere.
Scientists do not yet know the atmosphere’s exact makeup. Options include a dense carbon dioxide layer like a hotter Venus or a sulfur dioxide-rich gas like what comes from Jupiter’s volcanic moon Io. Dang et al. want to tell whether the atmosphere resembles Venus or an extreme Io by watching the planet at longer infrared wavelengths with JWST.
The paper ‘A Highly Reflective Atmosphere on the Lava World TOI-561 b Revealed by JWST/NIRSpec Phase Curve’ appeared in The Astronomical Journal with DOI 10.3847/1538-3881/ae9763. The paper lists Samuel Boucher as first author. He began the work as a student intern at the Trottier Institute for Research on Exoplanets while Dang held a Banting postdoctoral position there, and she continued supervising him after she joined Waterloo. The project grew from that internship into the published JWST study.
Anjali Piette of the University of Birmingham, an assistant professor of astronomy, said the result challenges current theories since strong stellar irradiation should have removed the atmosphere from a rocky planet like billions of years ago. Piette also raised questions about whether the planet started with an unusually large gas supply or its molten-rock ocean feeds it. ‘Our discovery challenges current theories,’ Piette said.
On Aug. 26, 2026, the team’s 37-hour continuous NIRSpec observations accounted for stellar granulation along with the planet’s phase curve and eclipse. The work produced a dayside emission spectrum that holds up against stellar variability. Energy-balance calculations and general circulation model comparisons show the observations require high reflectivity plus limited day-to-night heat transport, a mix that does not fit a bare-rock surface.
Past density and eclipse-only measurements suggested an atmosphere might exist, while the full-orbit data set confirms it reaches around the planet and shows cloud-driven reflectivity. The finding argues against the view that strong stellar radiation strips atmospheres from all ultra-short-period rocky planets.
On Aug. 26, 2026, Dang et al. said JWST’s MIRI instrument could detect silicon dioxide clouds above 3 sigma in 5-12 micron phase curves within 18 months, if silicates dominate the reflective layer. “MIRI 5-12 micron phase curves will detect SiO2 cloud absorption features at >3 sigma within 18 months if the reflective layer is silicate-dominated.” Dang et al. said.
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