MAVEN spacecraft in Mars orbit. Illustration of the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft in orbit around Mars. The NASA spacecraft launched on 18 November 2013 and reached Mars orbit on 22 September 2014. It has been studying the evolution of the Martian atmosphere. It is thought Mars used to have a thick atmosphere that made it warm enough for there to be liquid water on the surface. Data collected by MAVEN is helping scientists understand how and why most of that atmosphere was lost. One factor is the distance of Mars from the Sun, with the rate of water loss 10 times more when Mars is closest to the Sun, compared to when it is at its maximum distance from the Sun.