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

The water vapor has frozen out into the polar ice caps and permafrost as Mars has cooled. Evidence suggests that Mars had liquid water in the distant past, indicating a substantial atmosphere. However, as the planet cooled over time, the water vapor in the atmosphere froze out into the polar ice caps and permafrost. This process is still ongoing, and the current atmosphere is mostly composed of carbon dioxide with traces of other gases.

Evidence of Liquid Water in Mars' Distant Past Suggests That