At 01:33 AM 12/2/2005, David Locklear wrote: >According to a news article today, the planet Mars >has subsurface pockets of frozen water. >Are they talking ice caves? >Or do they mean ice below the soil? >I am imagining giant lave tubes with frozen rivers.
All the above. In the early stages of planet formation--Earth included--there was a tremendous bombardment by meteorites (term used loosely) which effectively reduced the surface of the planets to rock rubble to a depth of a kilometer and more. These show up locally today as impact craters and the great size of their underground extent makes excellent aquifers. Later many of these areas were covered with lava flows and some were isolated and still contain primordial water. As most of you know lava and associated extrusive igneous material is quite porous due to cracking and layering and often contains rather sizable conduits we call lava tubes. All of these conditions allow for the passage and pooling (however grand or minuscule) of water. Also it must be considered that magma masses have cooled and shrunk leaving large subsurface cavities at a depth of several kilometers. The surface temperature on Mars ranges from more than a hundred degrees below 0 Celsius to ten or twenty degrees above 0--on a good day. That means that liquid water could exist on the surface. But the atmospheric pressure on Mars is so low that water won't puddle as a liquid very long--it will boil away at temperatures well below freezing. In fact, solid surface water (call it ice, if you like) readily sublimes at those pressures (as it does on Earth at even greater pressure). Water, incidentally, can remain in a liquid state on Mars at below-freezing temperatures because it is probably quite salty--as are our Earth oceans--down to temperatures of about -40. But far and away most water on Mars is probably tied up as subsurface ice in a soil slurry similar to permafrost at depths ranging from a few meters to several hundred meters (depending on the latitude and other factors). On warm days this near-surface ice can melt and form springs on cliff sides and run for some distance as surface streams until it is absorbed back into the soil or sublimed by the atmosphere. An interesting effect of this near-surface melting is the softening of otherwise stark surface features such as impact craters, which slump and flatten and even fill in as the melted material tends to flow and seek to level itself, much as ice cream does when it melts. In this same context it must be assumed that although most of the core of Mars has cooled (relative to that of Earth, at least) there is still sufficient heat to hold massive reservoirs of liquid water at depth. Getting to that water, however, may not be an easy task. There is lots of subsurface water on Mars. But getting to it through the frozen soil will require more than a long-handled shovel. You'd be well advised to pitch a good pick or two into the tool box when packing for your trip--and maybe a still to get the salt out once you get some usable chunks. --Ediger _______________________________________________ Texascavers mailing list [email protected] http://texascavers.com/mailman/listinfo/texascavers_texascavers.com
