Water and Sulfur in Mars' soil

Through a complete accident, Spirit, has discovered water in the soil of mars according to this article. Spirit essentially tripped on soil it then found to have water bound to minerals in it. The rover tripped, because this area was softer than expected and it sank. In the process of getting unstuck, Spirit got some of the soil trapped in its wheels. Over the long Martian winter, when the rover has to stay mostly dormant and immobile, Spirit had lots of time to examine it unexpected companion. Scientists do not know exactly why the soil has water in it, but it proves Mars once had some form of flowing water. The two best guesses so far are that the soil marks an ancient gas vent or groundwater well. More discoveries of this type of soil will eventually explain which theory is correct.