A planet orbiting so close to its star that it completes a full year in less than 11 hours shouldn't be able to hold an atmosphere. Yet NASA's James Webb Space Telescope has found the strongest evidence yet that TOI-561 b, an ultra-hot rocky world about 1.4 times Earth's size, is wrapped in a thick layer of gas.
The discovery challenges a long-held assumption about small planets in extreme orbits. Researchers expected TOI-561 b to be a bare, airless rock — scorched by radiation and stripped of any gases it might have once held. Instead, the telescope's infrared sensors revealed something unexpected: the planet's dayside is about 1,700°F cooler than it should be if it were naked rock exposed to its star.
That temperature gap points to one explanation: a dense atmosphere thick enough to shuffle heat around the planet. Strong winds would carry warmth from the permanently sunlit dayside to the perpetually dark nightside, cooling the exposed face in the process. Water vapor and silicate clouds in that atmosphere would also absorb and reflect starlight, making the planet appear cooler than it actually is.
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Start Your News DetoxA Wet Lava Ball in Equilibrium
TOI-561 b orbits an ancient, iron-poor star — twice as old as our Sun — at a distance of less than one million miles. For comparison, Mercury orbits our Sun at roughly 40 times that distance. The planet's surface is so hot that rock melts into magma oceans. Yet somehow, it's holding onto gas.
The key, researchers think, lies in a delicate balance. As the magma ocean releases gases into the atmosphere, those same gases are being pulled back down into the planet's interior. Tim Lichtenberg, a co-author from the University of Groningen, describes it plainly: "It's really like a wet lava ball." For this equilibrium to work, TOI-561 b must be far richer in volatile compounds — water, carbon dioxide, and other gases — than Earth is.
Lead researcher Johanna Teske at Carnegie Science noted that what really sets this planet apart is its anomalously low density. "It is less dense than you would expect if it had an Earth-like composition," she said. The atmosphere, combined with an unusually small iron core, explains why the planet weighs less than standard models predict.
The observations come from 37 continuous hours of James Webb infrared spectroscopy, during which TOI-561 b completed nearly four full orbits. The team is now analyzing the full dataset to map temperatures across the entire planet and narrow down what gases make up its atmosphere. The findings, published in The Astrophysical Journal Letters, suggest that even planets in the harshest environments can hold onto substantial atmospheres — opening new questions about where life might theoretically exist in distant star systems.
