Life on Mars?
There was once a time when scientists suspected life on Mars. This seemed a logical theory considering there were polar ice caps on its surface. We now know that the atmosphere has a pressure that varies between 5 and 10 millibars (much lower than anyone had suspected until Mariner 4 made radar occultation measurements). It is almost entirely carbon dioxide, but contains some water vapor and other trace gases. The polar caps are partly water ice and partly frozen carbon dioxide, but there are differences between the northern and southern polar caps, as there is between a polar cap seen in the Martian winter and a polar cap seen in the Martian summer. This means that once there was water on Mars. Life can live in extreme environments so this is what leads scientists to believe that life was once on Mars or that life could one day be possible on the red planet. (1)