Emission observability of lava planets using the JWST MIRI LRS slitless mode. Flux ratio is computed using radiative-convective models with temperature profiles shown in Fig. 3. The flux is given for a wavelength of 9 μm, where the presence of SiO is expected to cause a broad emission feature. Error bars are simulated for 20 h of observations (3 eclipses) and binned to R = 10. The highlighted region indicates the optimal magnitude range for the MIRI LRS mode. The colour of each planet denotes its -stellar temperature. Ideal targets have high flux ratio, large surface temperature and fall between 9.5 and 5.5 J magnitude.