The ionosphere of Mars plays a critical role in the loss of atmospheric gases and water to space. MAVEN has provided the first measurements of the composition of the ionosphere of Mars since Viking in 1976. Unlike Viking, which provided measurements at only one time of day, MAVEN has generated the first map of the full day/night structure of the ionosphere.
These two images show how the densities of the two main ions, O2+ and O+, depend on altitude and time of day. The global structure of the ionosphere, which is illustrated by these images, affects how much water escapes from Mars. In these images, the view is from the North Pole looking down and the planet is not to scale. [More at link]