An interpretation of the anomalously low mass of mars

Conventionally the models of the solar nebula have been constructed so that the surface density of the nebula is a monotonic function of the heliocentric distance. This mass distribution is not consistent with the observed mass distribution of planets, in particular, the Mars drop (the anomalously low mass of Mars). In order to explain this Mars drop, some researchers adopt processes to take mass out of the Mars region, and the approach taken so far is from the point of view of planetary formation theory. Here we present our new calculations of the evolution of the solar nebula. We find that the surface density in the nebula is not monotonic and that there is a minimum in the Mars region. This naturally fits the planet mass distribution, especially the Mars drop. We suggest that the existence of this minimum leads to the low mass of Mars in the following three ways. (1) The low surface density of the Mars region gives a low mass supply, and (2) it gives a low rate of planetesimal formation from dust. (3) The low surface density in the Mars region preferentially makes Mars a leftover protoplanet without gaining much mass during chaotic growth, the last stage of planet formation.