NASA'S MAVEN spacecraft is answering the question: What happened to Mars' Atmosphere!? We know Mars has undergone tremendous changes over its lifetime. Mars was once much warmer, with oceans of liquid water, and much higher surface pressures. Today, Mars is a cold, arid planet with a thin atmosphere. So; What happened!??
Besides an exciting opportunity to observe Comet Siding Spring in November 2014, the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft is sampling Mars' atmosphere to try to answer that question. MAVEN was launched in November, 2013 to explore the Martian atmosphere and determine how fast it is being eroded by the solar wind and how quickly it is losing its water. To learn more about Mars and its history, check out the following sites.
The largest, single, challenge for astronauts traveling to Mars will be to overcome exposure to solar storms and radiation.