Planetary equilibrium temperature

The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were in radiative equilibrium, typically under the assumption that it radiates as a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is assumed to be irrelevant; the equilibrium temperature is calculated purely from a balance with incident stellar energy.

Source: Wikipedia — Planetary equilibrium temperature (CC BY-SA 4.0)