There are tantalizing indications emerging from the thousands of infrared images taken so far by NASA’s Mars Odyssey spacecraft that Mars experienced a series of environmental changes during active geological periods in its history. “We knew from Mars Global Surveyor that Mars was layered, but these data from Odyssey are the first direct evidence that the physical properties of the layers are different. It’s evidence that the environment changed over time as these layers were laid down,” said Dr. Philip Christensen, principal investigator for Odyssey’s camera system and professor at Arizona State University, Tempe. “The history of Mars is staring us in the face in these different layers, and we’re still trying to figure it all out.”