Temperature distributions and thermal phase curves of the TRAPPIST-1 e system. Panel a: snapshot of the effective emission temperature of TRAPPIST-1 e. Panel b: snapshot of the surface temperature distribution of a hypothetical tidally locked airless exomoon. Panel c: meridional mean effective emission temperatures of: TRAPPIST-1 e (red line), a tidally locked airless exomoon (blue line), and an exomoon with uniform temperature (dashed line). Panel d: exomoon thermal phase curves, i.e. the ratio of the lunar infrared emission to the stellar infrared emission. The green, cyan, and dark blue lines represent tidally locked airless exomoons with radii of 1738 km, 2400 km, and 3000 km, respectively. The dashed line shows the thermal phase curve of an exomoon with uniform temperature and a radius of 3000 km. The exomoons orbit at 33 300 km around TRAPPIST-1 e, and the orbital period is 0.876 Earth days. The thermal phase curves are integrated over wavelengths from 5 to 50 μm.