Atmosphere on Mars 

An impressive view of the Martian atmosphere (Copyright Calvin J. Hamilton)

Relative to that on Earth, Mars has quite a different atmosphere in terms of chemical composition. Composed primarily of carbon dioxide, humans would find it a hard time to breathe. The percent by composition on the atmosphere are as follows:

Even with the thinness of this atmosphere, visible clouds are able to form high above the ground. Plumes of smoke sometimes swirl about volcanoes and occasionally, water frost covers the ground during winters. Could this tiny amount of moisture be the trace remains of a once water-flourished planet? Sure can.

As seen in this picture, cirrus clouds float high above the surface (Copyright Calvin J. Hamilton).