Just imagine this scene. You’re on Mars, in Gale crater, with Curiosity. The sun has just set, and the temperature is falling rapidly. You look up. You see brilliant, wispy clouds, still sunlit even though night has fallen where you’re standing. They’re high in elevation, so the Sun can still reach them. As you stand there, skygazing, feeling increasingly chilled, the noctilucent clouds waft along in the Martian air, dimming from east to west as the Sun sets on them.
Curiosity has, in fact, been looking up after sunset recently. It’s been taking Navcam photos, and the camera’s reasonably broad field of view (45 degrees) lets it take in a lot of clouds, giving all of us back on Earth a chance to see them, too.