Water on Mars - Page 12

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Barsoomer


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PostPosted: March 27, 2012 3:10 PM 

Ben, the researchers say they have observed terrestrial analogues in the Antarctic. That site might be more relevant than most terrestrial locations.

Also, they say no researchers have come up with an alternative explanation that the other researchers actually believe. The TSLs were specifically chosen in non-dusty areas, which would seem to make dust avalanches unlikely, for example.

Nobody says this is confirmed, simply that the evidence is getting stronger, and cannot be casually dismissed.

Ben


Posts: 2270

Reply: 222



PostPosted: March 27, 2012 4:39 PM 

Barsoomer; For liquid phase water to be expelled from the subsurface , a porous avenue must be available and there must be a pressure gradient.

We don't know how thick a permafrost layer could be on Mars but there are suggestions that it could be at least several meters.

This permanently ,frozen layer would extend downward or inward from any exposed surface including the walls and slopes of the craters where purported seeps occur.

Therefore permafrost eliminates two or more of the requirements for liquid seeps.

And again I don't think this is casual dismissal but application of known physical
parameters.

Barsoomer


Posts: 344

Reply: 223



PostPosted: March 27, 2012 8:01 PM 

Ben, I don't have the knowledge or experience to personally evaluate your reasoning here. But I have to ask: if the mechanisms are so obvious that the whole idea can be dismissed in four sentences, why is it seemingly taken seriously by Scientific American? Why are there no resounding refutations in this year's LPSC abstracts, a year after the one that proposed the idea?

Ben


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Reply: 224



PostPosted: March 27, 2012 8:27 PM 

Barsoomer; My reply would be one that I have mentioned earlier in my posts.

Many of the researchers apparently have limited experience with the science associated with ground water.

Serpens


Posts: xxx

Reply: 225



PostPosted: March 27, 2012 11:30 PM 

Barsoomer. There are a couple of points that need to be considered. They occur in mid to high latitudes and predominantly in the south where the winters are colder and longer. They appear in early spring where the temperatures would result in carbon dioxide ice sublimating rather than permafrost melting. They also occur on sand dunes and crater mounds where as Ben points out there could be no hydrological head in the absense of precipitation. The link shows examples of active gullies on such dunes.

http://asterisk.apod.com/viewtopic.php?f=29&t=22603

The water cause for gullies is just one (very low probability) possibility and as Ben has succinctly explained, hard to support given the physics.

Barsoomer


Posts: 344

Reply: 226



PostPosted: March 28, 2012 1:31 AM 

Yes, there are lots of gully-like features where water seems unlikely and that can easily be explained by other mechanisms. But one must be careful about generalizing from the part to the whole.

The authors were careful to exclude such cases and focus on a carefully selected subset that cannot be easily explained, and display seasonal variations that are consistent with the brine hypothesis.

My opinion is that the jury is still out on this one while we await further evidence.

Barsoomer


Posts: 344

Reply: 227



PostPosted: May 7, 2012 11:38 AM 

[link]

[link]

Direct evidence that pressure on early Mars was at least 120 MBars.

Ben


Posts: 2270

Reply: 228



PostPosted: May 8, 2012 11:30 PM 

Barsoomer; I have read both of the articles and agree the atmosphere was probably more dense during the warm wet period in Mars History.

What connotations do you attach to that probability?

Barsoomer


Posts: 344

Reply: 229



PostPosted: May 9, 2012 12:16 AM 

Just noting it for the record on this thread. Every bit of evidence helps to make the picture clearer.

Barsoomer


Posts: 344

Reply: 230



PostPosted: May 13, 2012 10:35 PM 

http://www.sciencemag.org/content/suppl/2012/05/02/336.6081.615-b.DC1/SciencePodcast_120504.pdf

Scroll down to the Arvidson interview.

Quote:

"You know, there's still a little bit of liquid water occasionally coming out based on the recent gullies and the other activity that we see."

Ben


Posts: 2270

Reply: 231



PostPosted: May 14, 2012 12:18 AM 

Barsoomer; It appears that Arvidson, by the excessive use of the term "upwelling" is not well versed in the field of hydrogeology.
We use "artesian" for situations on earth where hydrostatic head in sealed aquifers allows ground water to reach the surface.

They are rather rare and the larger ones are present in Australia and Russia.
Many small , local occurences are called "springs".
Other than that I basically agree with his comments.

Barsoomer


Posts: 344

Reply: 232



PostPosted: May 14, 2012 3:16 PM 

Ben, thanks for the clarification. Maybe there is some hope of comparative "oases" where springs might yet occur on Mars. I expect the greatest chance for these would be at the bottom of deep valleys. It is interesting that the landing site for MSL is at a depth of 3 kilometers below the elevation corresponding to the triple-point pressure, so maybe there is potential for some excitement in the earliest part of the mission, before the rover starts its climb of the mound.

Ben


Posts: 2270

Reply: 233



PostPosted: May 14, 2012 4:07 PM 

Barsoomer; The depth at the bottom of Gale would normally have a ring like lake surrounding the central high and I expect at one time it did.
Apparently changes in the climate have caused it to disapate.
Other deep craters may have ice covered by dust that preserved it.

Barsoomer


Posts: 344

Reply: 234



PostPosted: May 14, 2012 10:36 PM 

link

According to the above link, there may still be some ice trapped in the mound deposits at Gale.

SHARAD recorded some subsurface echoes near the landing ellipse, which are probably layered deposits, but could be ice.

Ben


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PostPosted: May 15, 2012 12:40 AM 

The only change I would make in the proposed scenario is that the ice/dust accumulated on an early central mound because of its topography. (ice capped mtn)
This caused it to further increase in height,forming the current cental dome, without the need for later erosion to remove material in the surrounding low ring.
It was never deposited there to begin with.

Kevin


Posts: xxx

Reply: 236



PostPosted: May 15, 2012 5:15 AM 

Well it would not take long for Earth to look like Mars if it lost its atmosphere and the Oceans sublimated eh?

[link]

Intersting that we don't fully know how much water might be beneath the surface.

Ben


Posts: 2270

Reply: 237



PostPosted: May 15, 2012 12:51 PM 

This chart shows the percentage of earths water that is ground water which by nature is located in porous sediments.

Since Mars has a much smaller percent of sediment my guess is that the water below the surface is not very large.


[link]

Barsoomer


Posts: 344

Reply: 238



PostPosted: May 15, 2012 3:14 PM 

On the other hand, Mars is further from the sun, so it should have received more water in total. There must be a lot of subsurface ice.

Ben


Posts: 2270

Reply: 239



PostPosted: May 15, 2012 3:58 PM 

Barsoomer; er, for subsurface ice there has to be pore space (ie sediments) so the presence of large areas of basalt and impactites won't have much pore space to contain ice.

Barsoomer


Posts: 344

Reply: 240



PostPosted: May 15, 2012 5:12 PM 

Well, the water has to go somewhere. Buried glaciers don't need pore space, do they? What about ice lenses? They need pore space to start, but after that, they create their own space.

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