New Delhi, Dec. 13 -- Astronomers using the James Webb Space Telescope (JWST) say they have found the strongest evidence so far that a rocky planet outside our solar system may have an atmosphere - a discovery that challenges long-held assumptions about small, super-hot worlds, Nasa reported on Thursday. The planet, called TOI-561 b, orbits a 10-billion-year-old 280 light-years from Earth. It circles its star extremely closely, completing one orbit in less than 11 hours - far nearer than Mercury is to the Sun. Because of this intense proximity, scientists had believed such planets would lose any atmosphere long ago. But new JWST data suggests otherwise. Researchers report that TOI-561 b appears to be wrapped in a thick layer of gas above what is likely a global ocean of molten rock. This atmosphere could help explain why the planet has a surprisingly low density. Although its radius is about 1.4 times that of Earth, it is lighter than expected if it were made only of rock and metal. Johanna Teske, a scientist at Carnegie Science Earth and Planets Laboratory and lead author of a paper published on Thursday in the Astrophysical Journal Letters, says one possibility is that the planet formed in a very different chemical environment. Its host star is old and iron-poor, located in the Milky Way's "thick disk", suggesting the planet may reflect the composition of worlds formed when the universe was young. However, composition alone did not explain the low density. Scientists suspected an atmosphere might be making the planet look larger and affecting its temperature. To test this, they used JWST's NIRSpec instrument to measure the planet's dayside heat as it passed behind its star. JWST measured 3,200degF (1,800degC). The cooler-than-expected temperature supports the idea that gases are circulating heat around the planet....