Astrophysics (Index)About

equilibrium temperature

(Teq, Teq, planetary equilibrium temperature)
(temperature a planet would have if it were an externally-heated black body)

A planet's equilibrium temperature (Teq or planetary equilibrium temperature) is the temperature a planet would have given its incoming electromagnetic radiation (i.e., from its host star) if it were a simple black body, thus not subject to atmospheric windows, internal heat sources, etc. One simple determination calculates it from the host star's luminosity (calculable from its radius and temperature) along with the distance between star and planet. Sometimes the term is used taking albedo into account as well, and perhaps sometimes including other factors. Some cited equilibrium temperatures (sources vary):

planetTeqactual surface temperature
Mercury449 K440 K
Venus328 K730 Kdue to greenhouse effect
Earth279 K287 Kgreenhouse
Mars226 K218 K
Jupiter122 K120 K
Saturn90 K88 K
Uranus64 K59 K
Neptune51 K48 K
Pluto44 K37 K
55 Cancri e1958 K1613-2709 Knight/day
GJ 1132 b600 K
GJ 1214 b555 K
Proxima b235 K
WASP-67b1050 K

In the case of extra-solar planets, sometimes the calculated equilibrium temperature is the only temperature determination, but transit spectroscopy and spectrography over the course of the planet's orbit may offer an independent temperature determination for comparison.

Further reading:

Referenced by pages:
greenhouse effect
stellar flare