  The problem of the formation of the Moon is still not explained
satisfactorily. While it is a generally accepted scenario that the last giant
impact on Earth between some 50 to 100 million years after the starting of the
formation of the terrestrial planets formed our natural satellite, there are
still many open questions like the isotopic composition which is identical for
these two bodies. In our investigation we will not deal with these problems of
chemical composition but rather undertake a purely dynamical study to find out
the probability of a Mars-sized body to collide with the Earth shortly after
the formation of the Earth-like planets. For that we assume an additional
massive body between Venus and Earth, respectively Earth and Mars which formed
there at the same time as the other terrestrial planets. We have undertaken
massive n-body integrations of such a planetary system with 4 inner planets (we
excluded Mercury but assumed one additional body as mentioned before) for up to
tens of millions of years. Our results led to a statistical estimation of the
collision velocities as well as the collision angles which will then serve as
the basis of further investigation with detailed SPH computations. We find a
most probable origin of the Earth impactor at a semi-major axis of approx. 1.16
AU.
