Most clouds on Mars hover no more than about 37 miles (60 kilometers) in the sky and are made of frozen water. But these shimmering clouds photographed by the Curiosity Rover sit at a higher altitude, where the air is much colder. This likely means that the higher clouds are made from frozen carbon dioxide. The Curiosity’s panoramic Mast Camera, or Mastcam, captured the clouds just after sunset, showing ice crystals that were able to catch the fading light and appeared to shine against the sky. “These twilight clouds, also known as “noctilucent” (Latin for “night shining”) clouds, grow brighter as they fill with crystals, then darken after the Sun’s position in the sky drops below their altitude,” the lab said. “This is just one useful clue scientists use to determine how high they are.”