A Cascading Slice of Martian History

Every now and again, I get a sudden reminder that Mars is not just an ochre point of light in the sky. It's a world. Points of light have no dimension, just color and magnitude. But worlds are rich, diverse, with varying terrains, geography, forces in motion and in balance. The difference between viewing a planet from afar and from up close is the difference between seeing it and knowing it. Mars is like that. I've seen it countless times by eye and by telescope. Even when it's relatively close ...