![]() ![]() Finally, the CO 2 of the atmosphere can itself condense at high altitudes to form hazes of dry ice crystals. These often form around mountains, just as happens on our planet. Second are water-ice clouds similar to those on Earth. First there are dust clouds, discussed above. Several types of clouds can form in the martian atmosphere. Salty water is therefore sometimes able to exist in liquid form on the martian surface, under the right conditions. However, salts dissolved in water lower its freezing point, as we know from the way salt is used to thaw roads after snow and ice forms during winter on Earth. At a pressure of less than 0.006 bar, the boiling point is as low or lower than the freezing point, and water changes directly from solid to vapor without an intermediate liquid state (as does “dry ice,” carbon dioxide, on Earth). But even if the temperature on a sunny summer day rises above the freezing point, the low pressure means that liquid water still cannot exist on the surface, except at the lowest elevations. Part of the problem is the low temperatures on the planet. In most ways, however, the depiction of Mars in this movie is remarkably accurate.Īlthough the atmosphere contains small amounts of water vapor and occasional clouds of water ice, liquid water is not stable under present conditions on Mars. Astronomers have noted that the martian winds could not possibly be as forceful as depicted in the film. The issue of how strong the winds on Mars can be plays a big role in the 2015 hit movie The Martian in which the main character is stranded on Mars after being buried in the sand in a windstorm so great that his fellow astronauts have to leave the planet so their ship is not damaged. In the absence of surface water, wind erosion plays a major role in sculpting the martian surface ( Figure 10.24). ![]() It is this fine dust that coats almost all the surface, giving Mars its distinctive red color. The wind is able, however, to loft very fine dust particles, which can sometimes develop planet-wide dust storms. While winds on Mars can reach high speeds, they exert much less force than wind of the same velocity would on Earth because the atmosphere is so thin. The proportions of different gases are similar to those in the atmosphere of Venus (see Table 10.2), but a lot less of each gas is found in the thin air on Mars. (This is how thin the air is about 30 kilometers above Earth’s surface.) Martian air is composed primarily of carbon dioxide (95%), with about 3% nitrogen and 2% argon. The atmosphere of Mars today has an average surface pressure of only 0.007 bar, less than 1% that of Earth. Therefore, the guiding principle in assessing habitability on Mars and elsewhere has been to “follow the water.” That is the perspective we take in this section, to follow the water on the red planet and hope it will lead us to life. But where (and how) should we look for life? We know that the one requirement shared by all life on Earth is liquid water. Of all the planets and moons in the solar system, Mars seems to be the most promising place to look for life, both fossil microbes and (we hope) some forms of life deeper underground that still survive today. Summarize the evidence for and against the possibility of life on Mars.Describe the evidence for the presence of water in the past history of Mars.Explain what we know about the polar ice caps on Mars and how we know it.Describe the general composition of the atmosphere on Mars.By the end of this section, you will be able to: ![]()
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