A simple test of the induced nature of the Martian tail

The cross flow direction of the interplanetary magnetic field is strongly correlated with the cross flow direction several hours earlier and later. This correlation allows a simple test of the nature of the magnetic field in the Martian magnetotail. If the magnetotail is entirely induced, then the cross tail direction of the magnetic field should be along the direction of the cross flow component just upstream of the bow shock. We find that these directions of the tail field and the interplanetary magnetic field are so highly correlated that any intrinsic magnetic field of Mars must make at most a small contribution to the magnetotail. We estimate an upper limit to the magnetic moment of Mars to be about 4 × 10¹¹Tm³.