The structure of the magnetic field surrounding the planet Mars has been investigated using a fully three-dimensional hybrid particle code. The results of these simulations are found to agree well with Phobos 2 data. However, the results also indicate that the solar wind interaction with the planet Mars produces a magnetic environment around the planet that is unique among the planets of the solar system. This paper reports the findings from a series of large-scale, three-dimensional simulations and many two-dimensional simulations used to address numerical issues.¿ 1997 American Geophysical Union