Free Astronomy Magazine March-April 2026

36 ASTRO PUBLISHING roughly 1.4 times Earth’s, and an or- bital period less than 11 hours, TOI- 561 b falls into a rare class of objects known as ultra-short period exoplan- ets. Although its host star is only slightly smaller and cooler than the Sun, TOI-561 b orbits so close to the star — less than one million miles (one-fortieth the distance between Mercury and the Sun) — that it must be tidally locked, with the tempera- ture of its permanent dayside far ex- ceeding the melting temperature of typical rock. “What really sets this planet apart is its anomalously low density,” said Johanna Teske, staff scientist at Carnegie Science Earth and Planets Laboratory and lead au- thor on a paper published in The As- trophysical Journal Letters . “It’s not a super-puff, but it is less dense than you would expect if it had an Earth- like composition.” One explanation the team considered for the planet’s low density was that it could have a relatively small iron core and a man- tle made of rock that is not as dense as rock within Earth. Teske notes that this could make sense: “TOI-561 b is distinct among ultra-short period MARCH-APRIL 2026 R esearchers using NASA’s James Webb Space Telescope have detected the strongest evi- dence yet for an atmosphere on a rocky planet outside our solar sys- tem. Observations of the ultra-hot super-Earth TOI-561 b suggest that the exoplanet is surrounded by a thick blanket of gases above a global magma ocean. The results help ex- plain the planet’s unusually low den- sity and challenge the prevailing wisdom that relatively small planets so close to their stars are not able to sustain atmospheres. With a radius A thick atmosphere around broiling lava world by NASA/ESA/CSA NASA Webb Mission Team