2D thermal temperature maps (left column and colour bar) and maps showing ratio of atomic to molecular hydrogen, assuming chemical equilibrium, that would be present given the temperature maps (right column and colour bar) of KELT-9b in each bandpass. The hottest temperature is reached near the substellar point and is just over 5000 K whereas the lowest temperature is reached in the Spitzer bandpass at just under 2500 K. On all three maps, the dayside is mostly atomic hydrogen-saturated while across the terminator and over to the nightside, the ratio falls to near zero at the antistellar point.