A complete linear model for the Yarkovsky thermal force on spherical asteroid fragments

A linear theory for heat conduction in a spherical, solid and rotating body illuminated by solar radiation is developed. The recoil force due to the t hermally re-emitted radiation by the surface of the body is computed, inclu ding all the terms depending both on the body's rotation frequency and the mean motion of its revolution about the Sun. The present solution thus over comes a drawback of the previous approaches, which have been tailored separ ately either to the diurnal or to the seasonal variant of the so-called Yar kovsky effect, corresponding to different Limiting cases of the current the ory. Wk pay a special attention to compute the secular effects on the semim ajor axis of the body's orbit about the Sun. The results from the general m odel coincide with those of the previous approaches to a high level of accu racy, as the relative size of the additional "mixed" terms is smaller than 10(-3) for plausible parameter choices. This confirms that the use of the s implified formulae is warranted in the relevant Solar System applications.