All science begins in a star trek mode: go where no one has gone before and discover new things without knowing in advance what they might be. As researchers complete their initial surveys and accumulate a long list of questions, they shift to a Sherlock Holmes mode: formulate specific hypotheses and develop ways to test them. The exploration of Mars is now about to make this transition. Orbiters have made global maps of geographic features and composition, and landers have pieced together the broad outlines of the planet's geologic history. It is time to get more sophisticated.