US flag on Mars, artwork. Flag of the United States of America (USA) planted by astronauts exploring Mars. Mars is a rocky desert world with no surface water. The atmosphere is mostly carbon dioxide and surface temperatures are well below freezing. The thin atmosphere means that flags will need to made of a rigid material, rather than cloth. Human missions to explore Mars have been planned since the 1950s, usually involving a period of 10 to 30 years to develop the necessary technology and resources. The most recent US plan, NASA's Constellation Program, had a Martian mission as its ultimate aim, but as of 2010 has an uncertain future.