Free Astronomy Magazine March-April 2026

37 ASTRO PUBLISHING planets in that it orbits a very old (twice as old as the Sun), iron-poor star in a region of the Milky Way known as the thick disk. It must have formed in a very different chemical environment from the planets in our own solar system.” The planet’s com- position could be representative of planets that formed when the uni- verse was relatively young. But an exotic composition can’t explain everything. The team also suspected that TOI-561 b might be surrounded by a thick atmosphere that makes it look larger than it actually is. Although small planets that have spent billions of years baking in blaz- ing stellar radiation are not expected to have atmospheres, some show signs that they are not just bare rock or lava. To test the hypothesis that TOI-561 b has an atmosphere, the team used Webb’s NIRSpec (Near-In- frared Spectrograph) to measure the planet’s dayside temperature based on its near-infrared brightness. The technique, which involves meas- uring the decrease in brightness of the star-planet system as the planet moves behind the star, is similar to that used to search for atmospheres in the TRAPPIST-1 system and on other rocky worlds. If TOI-561 b is a bare rock with no atmosphere to carry heat around to the nightside, its dayside temperature should be approaching 4,900 degrees Fahren- heit (2,700 degrees Celsius). But the NIRSpec observations show that the planet’s dayside appears to be closer to 3,200 degrees Fahrenheit (1,800 degrees Celsius) — still extremely hot, but far cooler than expected. To explain the results, the team consid- ered a few different scenarios. MARCH-APRIL 2026 A n artist’s concept shows what a thick atmosphere above a vast magma ocean on exoplanet TOI-561 b could look like. Measurements cap- tured by NASA’s James Webb Space Telescope suggest that in spite of the intense radiation it receives from its star, TOI-561 b is not a bare rock. [NASA, ESA, CSA, Ralf Crawford (STScI)]