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ToSeek
2005-Aug-25, 04:31 PM
Water Flowed Recently on Mars, NASA Scientists Say (http://space.com/scienceastronomy/050824_mars_gullies.html)


Small gullies on Mars were carved by water recently and would be prime locations to look for life, NASA scientists said today.
...
The new study suggests water may still bubble to the surface of Mars now and then, flow for a short stretch, then boil away in the thin, cold air.

The conclusion is based on computer modeling of the atmosphere and how water would behave.

cran
2005-Aug-25, 05:01 PM
It's interesting, ToSeek...
and whilst I have much respect for NASA scientists, I'm not fully convinced about the conclusions as presented in the article... but I'll await any further developments with increased interest... :)

Fraser
2005-Aug-25, 05:33 PM
SUMMARY: NASA scientists think they've developed a strong case that liquid water created the strange gullies discovered on Mars a few years ago. These gullies might indicate underground sites of water, and could be a good place to search for life. Although Mars' environment is too cold, dry and low pressure to support liquid water, it could last a little while as it escaped from an underground reservoir. The lack of debris fields at the ends of these gullies suggests the water froze or evaporated before it reached the bottom.

View full article (http://www.universetoday.com/am/publish/water_create_gullies_on_mars.html)

What do you think about this story? Post your comments below.

VanderL
2005-Aug-25, 07:28 PM
Ok, so liquid water supposedly created the gullies, but what created the channels inside of which these gullies are found?

Cheers.

Duane
2005-Aug-25, 07:29 PM
VanderL, I am not sure what you are asking here. My immediate responce was "water of course, duh" but I want to make sure I understand what you are rferring to.

VanderL
2005-Aug-25, 08:33 PM
According to the study the gullies are apparently recent, if you look at the channel walls that show these short gullies (less than 500 yards) nothing else happened to the walls. How can such a process be recent?
Why are these walls "pristine" in adjacent areas, why didn't this process erode the walls over the long periods that are thought to have existed after the channels were formed? Or would you consider these channels to be "young" as well?

Cheers.

lswinford
2005-Aug-25, 10:39 PM
The line of the big one on the left and the smaller one on the right look like the thing that water would do, but three in the middle are fairly straightline (or at least look that way from the camera's perspective), so that could be simple dry sloughing. The alluvial fans would be consistent with a dry slide. So the water may have started it but didn't stay around for the full descent, still weakening the bank of that formation, so the ground gave way and continued the slide. Lots of things other than water could have purpetrated some of those land slides.

What was the source of such a concentrated flow of water? Were there indications on the tableland above of water flows or was this from subsurface flows that sprung out at the cliff?

And what's with the "pure" water description? Why did the water have to be "pure"?

alfchemist
2005-Aug-25, 11:03 PM
It seems, a few assumptions were made " that may not hold water": the type of liquid and the properties of the martian soil for which I don't quite remember complete data is available. Water was said to be saline. If that's the case, with the mechanism described, one would expect a salt deposit somewhere as this would not sublime with water. Time scale for such processes must also be presented.

cran
2005-Aug-26, 05:09 AM
Some valid points, guys ... and the reason I'm holding off rather than getting even slightly excited about this story... ;)

Yes the gullies, fans, etc could just as easily be formed by sand and wind (and even minor seismics)... <_<

The water (as ice) could have been (may be) the &#39;cement&#39; which holds the grains together... and then when exposed could sublimate without a liquid phase, and the grains simply obey gravity... but ... as alfchemist pointed out, there should be some evaporite residue or some hydrogeochemical residue (from soluble ions or hydrochemical interactions; eg, rust) with the grains. <_<

So, I patiently await some geochemical results... >tap, tap, tap< are we there yet? :P

Svemir
2005-Aug-26, 06:39 AM
Shouldn&#39;t it be easy to set up an experiment in a laboratory with Martian conditions?
Low pressure, low temperature, frozen surface, liquide water beneath and source of heating.
But, what is the source of heating on Mars?
According to a recent raport here on UT, Mars has been cold for quite some time (billions of years).

cran
2005-Aug-26, 07:39 AM
But, what is the source of heating on Mars?
Svemir, at the surface, heating from solar radiation is sufficient ... localised heating can also be achieved from boloidal impacts... but there is no need for heating ... at Martian atmospheric surface pressures, water ice will mostly sublimate (ie, will change from solid to vapour without a liquid phase)...
subsurface water may exist as a liquid or fluid if it is sufficiently saline, and under enough ambient pressure...
your suggestion of lab-based experiments under Martian surface conditions is a good one ... and should indicate whether liquid water can exist on the surface under any conditions now possible on Mars... :)

biknewb
2005-Aug-29, 11:26 AM
One thing in particular I don&#39;t understand:

Team scientists noticed that images of some of Mars&#39; gullies show that they taper off into very small debris fields or no debris fields at all suggesting that water rushing through the gullies rapidly froze and/or evaporated.
No matter how fast water flows, if it evaporates it will leave every single piece of debris behind. Where there&#39;s a gully there has to be an equal volume of debris somewhere.

regards

Svemir
2005-Aug-29, 12:40 PM
"Svemir, at the surface, heating from solar radiation is sufficient ...but there is no need for heating ..."
I&#39;m not talking about surface heating but about subsurface heating to make water liquid.
OK if water is enough saline it could be in liquid state down below, but how did it get there?
Besides, that subsurface water on Mars definitely excludes comets as depositors of water on Mars/Earth, cold Mars excludes vulcanos and tectonics as a mechanism of heating/transporting water to the surface.
I mean, permafrost in tundras on Earth is frozen and solar heating has little impact on it. Mars is colder, I assume it too has some kind of permafrost. (maybe I&#39;m wrong) How does water penatrate that layer?
Where is water deposited (to be exposed to enough ambient pressure)?

cran
2005-Aug-29, 04:28 PM
>thinks< I knew I packed up my reference books too soon...

Besides, that subsurface water on Mars definitely excludes comets as depositors of water on Mars/Earth
Why does it, Svemir?
Are you saying that the material of Mars is impermeable?
Do you have any reason to believe that Martian soil is impermeable?
Are you saying that comets could not have been, or were not, part of the original accretion process that formed the planets?
Or that the planets formed by some other process?

I mean, permafrost in tundras on Earth is frozen and solar heating has little impact on it.
Actually solar heating has a considerable effect on permafrost on Earth; more so in recent years ... surface depth to permafrost is not constant but varies over a number of cycles, the annual summer/winter variation being the most common ... permafrost, like other forms of terrestrial ice expands on freezing; in confined conditions, this leads to increasing ambient (there&#39;s a proper term for it, like &#39;hydrostatic&#39; (?) but my memory is rotten, and my books are packed in cartons ready for the move) pressures, cracking and shifting of mass ...
it is strong enough to crack, wedge, and break rocks apart in ... a large mass of ice (like a glacier) generates enough downward pressure that the ice at its base will lose its crystalline structure and flow ...
this flowing ice includes molecules of liquid water, despite the &#39;below-freezing&#39; temperature, and these tiny amounts of water can seep down into soil, and even into intergranular spaces in rocks, where they will eventually freeze again, expanding in the process ... given time, a growing glacier will carve out a U-shaped valley in the hard rock of young mountain in this way ...
permafrost won&#39;t carve out valleys, but surface and near surface meltwater will flow into cracks in the permafrost and into the country rock, where it re-freezes and expands, creating new zones of higher pressure and cracks ... one effect of this can be seen on the surface of the tundra - it is not flat, but bumpy with little hummocks (called &#39;drumlins&#39;, I think?) and dips ...
at greater depths, even under the permafrost, water is liquid ... and hypersaline, and it flows according to whatever pressure gradients are dominant, and will flow preferentially by pathways with the greatest pressure gradient ... usually, this means downwards, but this is not always the case (eg, artesian flow) ... the rate of flow depends upon the the height of the pressure gradient (or the difference in &#39;potential head&#39;) and the transmissivity of the medium (ie how much water can enter and pass through the medium) in hard rocks, the water will flow faster through open and interconnected cracks than through the intergranular pore spaces ... but in general terms groundwater flow is very slow and storage times can be on the order of millions of years (compared with thousands of years for the deep ocean water masses) ...
in the crystalline basement rocks, interpore water (&#39;connate&#39;?) has been dated to the age of the rock itself ... leading some to believe that the water was trapped as the rock first cooled and solidified ...
exactly how all this plays out on Mars will not be known until we have a lot more information ... which means deep mapping (seismics or more advanced GPR). :P

MarsArtGallery
2005-Aug-30, 04:17 AM
Hi all,

FYI, I&#39;ve added "Martian Gullies" to my web site. It contains a larger colorized version of the gullies image which shows the entire crater as imaged by the Narrow Angle camera.

The URL is http://www.marsartgallery.com/o_martiangully.html

There is also a wallpaper version cropped to approximately the same view as the gullies image that went out with the NASA press release.

Best Regards, Jim
http://www.marsartgallery.com

Svemir
2005-Aug-30, 06:18 AM
Are you saying that comets could not have been, or were not, part of the original accretion process that formed the planets?
Comets were all that it was. I mean, water was a part of the dusty disk where from planets came, so you can say that those chunks were comets.
I don&#39;t think water on Earth (or in/on other planets) came through a later early bombardment.


Are you saying that the material of Mars is impermeable?
Do you have any reason to believe that Martian soil is impermeable?

It&#39;s my simple logic: permafrost on Earth is let&#39;s say 1m, where only 10-30 cm on the top melts in summer. I assumed that on the Mars permafrost is much thicker, and that is mostly frozen rocks.
How on Earth (on Mars) liquid water from below penetrate that layer? :D

the rate of flow depends upon the the height of the pressure gradient (or the difference in &#39;potential head&#39;) and the transmissivity of the medium (ie how much water can enter and pass through the medium) in hard rocks,
I&#39;m aware of the power of water freezing to ice, but so much that it causes cracks where water comes on surface in amount enough to make 500 m gullies?
I still think that in their simulations they simply assumed that water got somehow to the surface of the Mars and that simulations show that it can be done.


QUOTE
Besides, that subsurface water on Mars definitely excludes comets as depositors of water on Mars/Earth


Why does it, Svemir?

I ment comets as impactors in the "early bombardment". At that point Mars was allready cold and with the conditions as now, how will impact of a comet deposit the water in the subsurface for later use (billions of years later)?
We definitelly have to drill the Mars.

cran
2005-Aug-30, 06:30 AM
Originally posted by MarsArtGallery@Aug 30 2005, 12:17 PM
Hi all,

FYI, I&#39;ve added "Martian Gullies" to my web site. It contains a larger colorized version of the gullies image which shows the entire crater as imaged by the Narrow Angle camera.

The URL is http://www.marsartgallery.com/o_martiangully.html

There is also a wallpaper version cropped to approximately the same view as the gullies image that went out with the NASA press release.

Best Regards, Jim
http://www.marsartgallery.com
You&#39;re a champion, MarsArtGallery&#33; :D

The longer image has much more detail, and the forms and discolouration in the lower fan do look more like the result of water deposition - the cropped version is looking at the wrong end of the image, where the slope is steep enough for mass movement without water... the larger and flatter fan (with included gullies) is a much more convincing argument ... I am now much more interested in further results... :D

cran
2005-Aug-30, 07:15 AM
Comets were all that it was. I mean, water was a part of the dusty disk where from planets came, so you can say that those chunks were comets. If so, Svemir, then you answered your own question, and refuted your own statement... :lol:

However, there is no indication in the admittedly scanty record of that period that "Comets were all that it was" - for either the primary accretion phase (~4.5Ga) or the "Late Bombardment" (~3.9Ga) - based on what has survived to date, the indications are that the vast bulk of material in the primary phase in the inner solar system were ferrosilicates and organics - and a sizable fraction of the "Late Bombardment" were also...


I don&#39;t think water on Earth (or in/on other planets) came through a later early bombardment. The evidence suggests that the vast bulk of the water on Earth was already present before the "late bombardment" (though many workers still argue that the first ocean and atmosphere were lost to space at this time - I don&#39;t agree with them); but a reasonable quantity of material seems to have been added at this time...


It&#39;s my simple logic: permafrost on Earth is let&#39;s say 1m, where only 10-30 cm on the top melts in summer. Better yet, let&#39;s say permafrost on Earth is 10-30m thick, and the top 1-3m melts in summer...


How on Earth (on Mars) liquid water from below penetrate that layer? If the pressure gradient is artesian, then it penetrates in exactly the same way, via cracks... however, the underlying layer doesn&#39;t need to rise up through the permafrost; it can flow horizontally or downwards and emerge as a spring flow or seep in the side of a surface slope - eg within a crater or wall of a larger gully ... this flow reduces the internal supporting pressure (ie, increases the vertical pressure gradient) which may lead to slumping (eg, as happens in the tundra) or to undermining of the solid ice (as happens in glaciers), depending upon the topography ... if liquid water can exist for any time at or near the surface then water rise can be achieved by a soil moisture process called &#39;capillary rise&#39; - on Earth this is caused by evaporation of soil moisture at or near the surface, which increases the pressure gradient for the water mass below, leading to replacement of the evaporated water - one sure sign of this is evaporite layers on the surface...


I&#39;m aware of the power of water freezing to ice, but so much that it causes cracks where water comes on surface in amount enough to make 500 m gullies? If there is sufficient water and sufficient pressure gradient and sufficient time... yes.


I ment comets as impactors in the "early bombardment". At that point Mars was allready cold and with the conditions as now, how will impact of a comet deposit the water in the subsurface for later use (billions of years later)? There is a group of workers who announced their findings that Mars was internally too cool by ~4Ga to maintain a geodynamo or plate tectonics or extended vulcanism (though how they reconcile that finding with Olympus Mons et al, I don&#39;t know...); that doesn&#39;t mean it was too cool to allow subsurface liquid water...

as for comet &#39;impactors&#39;, I would ask one of our &#39;thermodynamics&#39; experts to explain how much heat is released in a given comet impact - it&#39;s something on the order of a modern thermonuclear device ... more than enough to vaporise most (if not all) of the comet, and a fair bit of planetary surface at the impact site ... a region around the site (and to some depth) will remain hot enough for long enough to allow for liquid subsurface water, and even surface water, assuming sufficient atmospheric density at ~3.9Ga


We definitelly have to drill the Mars. Why?

Svemir
2005-Aug-30, 11:48 AM
To find water, ice....gold?:-)

cran
2005-Aug-30, 12:31 PM
Agreed. :D