In his paper, "WHERE is the MAGNETISM of MARS?", at http://milesmathis.com/marsmag.pdf , Mathis said:

"We know that although Mars has a low current magnetism, some of the rocks on Mars have a much higher residual magnetism. This has been taken to mean that Mars had more magnetism in the past. I think this is entirely possible, and that this reading is probably correct. But I do not think the magnetism was knocked off the planet by asteroids. No, this residual magnetism in the rocks on Mars is telling us something very important, not about Mars, but about the make-up of the Solar system in the past. It means that either Mars was not at its current orbital distance at that time, or the big outer planets were not. Something was vastly different. Given the asteroid belt and other glaring evidence, this is not hard to imagine. From this we see that my theory of planetary magnetism will give us the tool to work backward in time, rebuilding previous Solar system relationships. These rocks, which we find on other planets and moons as well, are like tablets with numbers on them. They will be very useful in future."