Surface temperature(Ts) is dependent on the heat flow from inside and other astonomic object. Heat flows through thermal conduction and radiation from inside and through radiation from outside.
The Physical quantity is proportional to the radiational pressure for solid.
In interplanetary space Edit
For example, at the boiling point of water (T = 373.15 K), the pressure only amounts to 3 micropascals (about 2 pounds force per square mile). If the radiation is directional (in interplanetary space, the overwhelming proportion of the energy flux comes from the Sun alone), the radiation pressure is tripled, to σT4/c; if the body is a perfect reflector, the pressure can be doubled again, to 2σT4/c. A solar sail at the distance where the equivalent radiation temperature is the boiling point of water could thus achieve about 22 µPa, or nearly 13 lbf/sq mi. Such feeble pressures are, nevertheless, able to produce marked effects upon minute particles like gas ions and electrons, and are important in the theory of electron emission from the Sun, of cometary material, and so on (see also: Yarkovsky effect, YORP effect).
Gravitational mass deep inside does radiate and the radiation propagate through the outside material to the surface. If the material is saturated, gravitational mass, that is, radiational pressure is additive. Even though not, Steady state partial radiational pressure is additive on the surface. Actual inside temperature is rather high.