Evidence of liquid water in Mars' distant past suggests that it had a substantial atmosphere compared to what it has presently.What happened to its water vapor?
A) The carbon dioxide in its atmosphere dissolved in the water and combined with surface rocks.
B) Its atmosphere was mostly hydrogen and helium. Mars' gravity is too weak to hold them.
C) The water vapor has frozen out into the polar ice caps and permafrost as Mars has cooled.
D) Mars initially had such a large Greenhouse Effect that the atmosphere became quite hot and slowly escaped.
E) It has now all been lost in space, including the carbon dioxide and water vapor.

Question

Quizplus · Accepted Answer

Evidence suggests that Mars' distant past had a thicker atmosphere, which would have allowed liquid water to exist on its surface. As Mars cooled down, the water vapor in the atmosphere would have frozen out into the polar ice caps and the permafrost, leading to a loss of much of the water in the atmosphere. This process may have been aided by the fact that Mars has a weaker gravity compared to Earth's, allowing some of the water to escape into space.

Evidence of Liquid Water in Mars' Distant Past Suggests That