Lighting effects

A piece of Mars: It’s winter in the southern hemisphere, and dunes like these are covered in bright white CO2 frost. The sun is near the horizon (shining from the top of the image), so it creates stark shadows. That can make doing science tough, but it’s the best way to show off the beauty of the dunes. Can you tell which way is up here, which way is down, and when you’re looking at a inherent change in the surface color vs. sun and shadows? (ESP_034922_1385, NASA/JPL/Univ. of Arizona)