Infrared Emissivity

The Infrared Emissivity of an object is a measure of how efficiently the object will emit infrared radiation. An object with an emissivity of one is a perfect blackbody and will absorb incoming radiation and re-emit it as thermal, infrared radiation based on its temperature. Objects with lower emissivity values will emit infrared radiation at lower rates. An object with an emissivity of zero will be perfectly reflective, absorbing and re-emitting none of the incoming energy as heat.

Location
The Infrared Emissivity property is located at the end of the Atmosphere section of the Surface tab of an object's properties panel. This section is only visible for Terrestrial Planets.

Surface Temperature
The emissivity of the atmosphere, $$\epsilon$$, affects the amount of heat energy that the atmosphere will radiate in all directions, including back down towards the surface of the object. The rate at which energy is added to the object's surface from this atmosphere heating, or the Atmosphere Power, is estimated as
 * $$P_{atm} = \frac{\epsilon}{2} \sigma T^4 4 \pi R^2,$$

where $$T$$ is the Average Surface Temperature of the object and $$R$$ is its Radius. This atmosphere power contributes to the total Energy Absorption Rate of the object, which is used to calculate its Average Surface Temperature.