Re: What caused the water\seas of Mars to disappear?

    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.