Asteroids are through and through cold, lifeless bodies. In the distant past, their bowels could be warm and even hot due to radioactive or some other heat sources. Since then, they have long cooled off. However, the internal heat never warmed the surface: the heat flux from the bowels was imperceptibly small. The surface layers remained cold, and only collisions from time to time caused a short-term local heating.
The only constant source of heat for asteroids remains the Sun, distant and therefore heating is very bad. A heated asteroid emits thermal energy into outer space, and the more intense it is, the stronger it is heated. Losses are covered by the absorbed part of the solar energy incident on the asteroid.
If we average the temperature over the entire illuminated surface, we get that for asteroids of a spherical shape, Continue reading