Webb reportedly finds signs of thick atmosphere on lava planet

The James Webb Space Telescope may have found a thick atmosphere around TOI-561 b, a scorching lava planet orbiting a distant star. Its day side is cooler than a bare rock would be, and the planet appears to reflect about 74% of the starlight that hits it. Anjali Piette, an assistant professor of astronomy at the University of Birmingham, said the result challenges current theories. "We would expect a heavily irradiated rocky planet like TOI-561 b to have lost its atmosphere billions of years ago."

Planet's extreme orbit

TOI-561 b is a little more than twice Earth's mass and about 1.4 times as wide. It circles its star in about 10.7 hours, so one side always faces the star while the other always faces away. The star is at least 10 billion years old and poor in heavy elements. An earlier 2025 study led by Johanna Teske found the planet's day side too cool for bare rock. Webb now measures it at about 3,200°F (2,050 K), while a dark, airless surface would be expected to reach about 5,300°F (3,200 K).

The best matches with the observed temperatures came from a thick atmosphere, with surface pressure between one and 10 times Earth's. The leading candidates for the reflecting layer are clouds of silicon dioxide or magnesium silicate, which could form on the day side near the edge where day turns to night. Clouds like these could work as a sunscreen, sending starlight back out before it heats the planet. The main gas is still unknown. It could be a thick layer of carbon dioxide, like a much hotter Venus, or it could be rich in sulfur dioxide, like the volcanic air of Io. Lisa Dang, the project lead, said the next big question is whether the atmosphere resembles Venus or an extreme version of Io. Longer-wavelength observations with Webb could help answer that.