Mysterious Mars: Water or No Water?

Now that the Mars Odyssey spacecraft has returned its first pictures, showing that its cameras work, it officially joins a long list of spacecraft that have studied whether or not water does or ever did exist at or near the surface of the Red Planet. But what will Odyssey do that hasn’t already been done? And why do we need yet another robotic probe orbiting Mars? Shouldn’t we be sending geologists by now? And hey, isn’t the real question, is there life on Mars?