Mars with clouds, artwork. The Sun is at upper left. This image can represent a Mars of the past, when its atmosphere was thicker and warmer and there was flowing water on its surface. Currently, Mars is a rocky desert world with no surface water. The atmosphere is mostly carbon dioxide and Martian surface temperatures are well below freezing. Most of the water and atmosphere were lost to space, or locked up in underground deposits of ice. This image can also represent the planet in the future, when humans have terraformed it to allow colonisation.