As is known, the study of the moon's thermal radiation provides a rather complete picture of the thermal behavior of its surface and also information on some of its other physical properties [e.g. Troitskii 1967]. The phase variation of the thermal radiation provides most of the information for such an analysis, and the method may also be applied to investigate the surfaces of Venus [Troitskii, 1964] and Mercury [Vetukhnovskaya et al., 1968]. For Mars, however, we cannot observe from the earth sufficiently large phase variations. In practice, it is only really possible to observe the more or less completely illuminated side of Mars.