|MadSci Network: Astronomy|
There are many different theories about the disappearance of the ancient seas that made such an impression on the Martian landscape long ago. The fact that such extensive examples of erosion apparently caused by water can be found at such diverse areas of Mars makes it pretty clear that at one time the surface did contain an abundant amount of water. Maybe not as much as the percentage on Earth, but certainly enough to make a difference in how the land was shaped. Now there may be theories, but no definite proof can be offered as long as we can only observe the planet from miles above. The only successful landings on the planet did not reveal any answer to this riddle, but they also landed at locations which did not promise any clues as to what happened to the water. The Mars Explorer probe, which was to have reported on the Northern polar ice field was unfortunately lost and could not help. Therefore, the answer cannot be made definitive at this time. The previous theories have all centered on the ancient seas somehow dropping below the surface and remaining in underground caverns. This theory is hard to reconcile with common sense. For instance, why would almost an entire planet's water supply sink? What forces of erosion could drive most of the water underground? There's really no satisfactory answer for this. Another theory is that the water on Mars became frozen and trapped in the planet's polar ice caps. However, even at its greatest limit the caps do not contain enough water to have made such strong erosion on the landscape at any time. A new theory is that the water on Mars is under the surface, but only maybe a few meters below it. The water has remained in an airtight caverns and still flows as a liquid because of pressure. When it reaches the surface through cracks in the ground, the water either instantly freezes or instantly boils away, depending on whether the crack occurs under sunlight or in deep gullies away from the heat. This theory is still being considered, but it has been connected to the recent news that scientists may have found evidence of liquid water below the polar ice on Mars. So rather than asking how the ancient seas of Mars disappeared, the answer may be that they have never really gone at all.
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