Free Astronomy Magazine May-June 2023

48 MAY-JUNE 2023 ASTRO PUBLISHING ets orbiting small active stars like TRAPPIST-1 can sustain atmospheres needed to support life. It also bodes well for Webb’s ability to character- ize temperate, Earth-sized exoplan- ets using MIRI. “These observations really take ad- vantage of Webb’s mid-infrared ca- pability,” said Thomas Greene, an astrophysicist at NASA’s Ames Re- search Center and lead author on the study published in the journal Nature . “No previous telescopes have had the sensitivity to measure such dim mid-infrared light.” In early 2017, astronomers reported the discovery of seven rocky planets orbiting an ultracool red dwarf star (or M dwarf) 40 light-years from Earth. What is remarkable about the planets is their similarity in size and mass to the inner, rocky planets of our own solar system. Although they all orbit much closer to their star than any of our planets orbit the Sun — all could fit comfortably within the orbit of Mercury — they receive comparable amounts of en- ergy from their tiny star. TRAPPIST-1 b, the innermost planet, has an orbital distance about one hundredth that of Earth’s and re- ceives about four times the amount of energy that Earth gets from the Sun. Although it is not within the system’s habitable zone, observa- tions of the planet can provide im- portant information about its sibling planets, as well as those of other M- dwarf systems. “There are ten times as many of these stars in the Milky Way as there Webb measures the temperature of a rocky exoplanet by NASA/ESA/CSA Margaret W. Carruthers Christine Pulliam A n international team of re- searchers has used NASA’s James Webb Space Telescope to measure the temperature of the rocky exoplanet TRAPPIST-1 b. The measurement is based on the planet’s thermal emission: heat en- ergy given off in the form of in- frared light detected by Webb’s Mid-Infrared Instrument (MIRI). The result indicates that the planet’s day- side has a temperature of about 500 kelvins (roughly 450 degrees Fahren- heit) and suggests that it has no sig- nificant atmosphere. This is the first detection of any form of light emitted by an exo- planet as small and as cool as the rocky planets in our own solar sys- tem. The result marks an important step in determining whether plan-