All bodies in the universe are constantly absorbing heat from surrounding thermal sources. This heat will be reemitted after a time lag. The temperature at each point of the heated surface will determine the frequency n of the photons sent out in such way that the total momentum associated to this process of energy loss depends on how the temperature is distributed at the surface. If the total momentum is not null, a thermal force will be produced whose intensity and direction will depend, fundamentally, on the temperature distribution at the surface: points with high temperature will re-emit photons with high frequencies and vice-versa. High frequency implies a great loss of momentum in the emission direction, and consequently great re-emission force in the opposite direction. But, not only the temperature can determine the frequency of the photons sent out but also the state at rest or movement of the body. When it presents some kind of movement (rotation, translation, etc.), the Doppler effect will change the frequencies of these photons and the frequency nu must be replaced by <FONT FACE=Symbol>n¢</FONT> . As a consequence, the resulting force will change too. In this work, we model the temperature variation (frequency variation) due to the Doppler effect and apply the new temperature distribution in the thermal re-emission model. The total force obtained by this "relativistic" thermal re-emission model has two terms: 1) the standard thermal re-emission force (without Doppler considerations) and 2) the relativistic correction of this force, similar to the standard Poynting-Robertson force. The thermal re-emission model presented here indicates that, in general, most of the several disturbing forces can be unified, providing a new and simple view for the understanding of the entire physics involved in such phenomena.
Thermal re-emission; Poynting-Robertson; Doppler; Unified model; Non-gravitational effects
