Equilibrium temperature

The planetary equilibrium temperature is a theoretical temperature that a planet would be at when considered simply as if it were 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 not considered, and one treats the theoretical black body temperature as if it came from an idealized surface of the planet.

Other authors use different names for this concept, such as equivalent blackbody temperature of a planet, or the effective radiation emission temperature of the planet. Similar concepts include the global mean temperature, global radiative equilibrium, and global-mean surface air temperature, which includes the effects of global warming.

If the incident solar radiation ("insolation") on the planet at its orbital distance from the Sun is I_o, the amount of energy absorbed by the planet will depend on its albedo a and its cross-sectional area:

${\displaystyle {P}_{in}={I_{o}}\left(1-a\right)\pi {{R}_{p}}^{2}}$

Note that the albedo would be zero (${\displaystyle a=0}$) for a blackbody. However, in planetology, more useful results are obtained by accounting for a measured or assumed planetary albedo ${\displaystyle a>0}$.

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