Presentations from the First Mars Express conference held in February
are available he

First Mars Express Conference Presentations.
http://sci.esa.int/science-e/www/obj...objectid=36537

These reports are longer than the 2-page abstracts seen from the Lunar
and Planetary Science Conference, some over 30 pages long.

A great image of dense fog in Valles Marineris is shown in this
report:

Reflectance of fog in Valles Marineris.
A. Inada
http://sci.esa.int/science-e/www/obj...objectid=36724

And this report has a beautiful full-color image of this very dense
fog:

Adsorption water driven processes on Mars.
D. Möhlmann
http://sci.esa.int/science-e/www/obj...objectid=36779

This article speculates on how adsorbed layers of water might be used
by microbes on Mars.

Valles Marineris is both low altitude and low latitude so should be
within the pressure and temperature range to permit liquid water for
this fog close to the surface.


cf.,

From: Robert Clark )
Subject: Supercooled liquid water can occur in clouds below 0 degrees
C.
Newsgroups: sci.astro, alt.sci.planetary, sci.geo.meteorology,
sci.geo.geology, sci.geo.mineralogy
Date: 2004-07-30 06:53:02 PST
http://groups.google.co.uk/groups?th=5bba314873613fde&


Bob Clark

Here's the link to that dense fog over Marineris:

http://sciforums.com/attachment.php?attachmentid=3999


Bob Clark


Robert Clark wrote:
Presentations from the First Mars Express conference held in February
are available he

First Mars Express Conference Presentations.
http://sci.esa.int/science-e/www/obj...objectid=36537

These reports are longer than the 2-page abstracts seen from the
Lunar
and Planetary Science Conference, some over 30 pages long.

A great image of dense fog in Valles Marineris is shown in this
report:

Reflectance of fog in Valles Marineris.
A. Inada
http://sci.esa.int/science-e/www/obj...objectid=36724

And this report has a beautiful full-color image of this very dense
fog:

Adsorption water driven processes on Mars.
D. Möhlmann
http://sci.esa.int/science-e/www/obj...objectid=36779

This article speculates on how adsorbed layers of water might be used
by microbes on Mars.

Valles Marineris is both low altitude and low latitude so should be
within the pressure and temperature range to permit liquid water for
this fog close to the surface.


cf.,

From: Robert Clark )
Subject: Supercooled liquid water can occur in clouds below 0 degrees
C.
Newsgroups: sci.astro, alt.sci.planetary, sci.geo.meteorology,
sci.geo.geology, sci.geo.mineralogy
Date: 2004-07-30 06:53:02 PST
http://groups.google.co.uk/groups?th=5bba314873613fde&


Bob Clark

In article .com,
"Robert Clark" wrote:

Here's the link to that dense fog over Marineris:

http://sciforums.com/attachment.php?attachmentid=3999

***{Wow! Has that been retouched? If not, that's one of the most
spectacular Mars photos I've ever seen! Of especial interest is what
appears to be a pool of liquid water showing at the far right of the
photo. Using the scale shown, the location of the pool is 129 km down
from the top edge, and 22 km in from the right edge. It looks like a
nice blue pool of water! And I see other apparent pools elsewhere, all
of them down in the low areas, some obscured by fog. The NASA folks, of
course, will explain it all away. "It's just another one of them pesky
false color photos," they will say. That's their standard comment
whenever lots of green or blue jumps out at the "lay" observer. --MJ}***

Bob Clark


Robert Clark wrote:
Presentations from the First Mars Express conference held in February
are available he

First Mars Express Conference Presentations.
http://sci.esa.int/science-e/www/obj...objectid=36537

These reports are longer than the 2-page abstracts seen from the
Lunar
and Planetary Science Conference, some over 30 pages long.

A great image of dense fog in Valles Marineris is shown in this
report:

Reflectance of fog in Valles Marineris.
A. Inada
http://sci.esa.int/science-e/www/obj...objectid=36724

And this report has a beautiful full-color image of this very dense
fog:

Adsorption water driven processes on Mars.
D. Möhlmann
http://sci.esa.int/science-e/www/obj...objectid=36779

This article speculates on how adsorbed layers of water might be used
by microbes on Mars.

Valles Marineris is both low altitude and low latitude so should be
within the pressure and temperature range to permit liquid water for
this fog close to the surface.


cf.,

From: Robert Clark )
Subject: Supercooled liquid water can occur in clouds below 0 degrees
C.
Newsgroups: sci.astro, alt.sci.planetary, sci.geo.meteorology,
sci.geo.geology, sci.geo.mineralogy
Date: 2004-07-30 06:53:02 PST
http://groups.google.co.uk/groups?th=5bba314873613fde&


Bob Clark

In article ,
Mitchell Jones wrote:

In article .com,
"Robert Clark" wrote:

Here's the link to that dense fog over Marineris:

http://sciforums.com/attachment.php?attachmentid=3999

***{Wow! Has that been retouched? If not, that's one of the most
spectacular Mars photos I've ever seen! Of especial interest is what
appears to be a pool of liquid water showing at the far right of the
photo. Using the scale shown, the location of the pool is 129 km down
from the top edge, and 22 km in from the right edge. It looks like a
nice blue pool of water! And I see other apparent pools elsewhere, all
of them down in the low areas, some obscured by fog. The NASA folks, of
course, will explain it all away. "It's just another one of them pesky
false color photos," they will say. That's their standard comment
whenever lots of green or blue jumps out at the "lay" observer. --MJ}***

***{After a considerable amount of digging and a few e-mails, I have
managed to get a definitive answer concerning the bona fides of the
photo linked above (i.e., at
http://sciforums.com/attachment.php?attachmentid=3999). This comes from
a source close to the European Space Agency who for the time being shall
remain nameless: "This is a real picture, no specific image processing
was used."

Daytime temperatures on Mars are frequently well above freezing, and I
have seen reports of daytime summer temperatures upwards of 20 deg. C,
though that is apparently unusual and those temperatures would probably
not be reached at the bottom of a deep, dark canyon such as Valles
Marineris. Under those circumstances, temperatures of 5 or 10 deg C
might be attained, but the maxima attained under more favorable
conditions would be very unlikely. Looking in an old edition of the
*Handbook of Chemistry and Physics*, I see that the vapor pressure of
pure distilled water at 5 deg C is 6.543 mmHg, and that the vapor
pressure at 10 deg C is 9.209 mmHg. Since water can only exist in liquid
form when its vapor pressure is less than atmospheric pressure, it
follows that atmospheric pressure in Valles Marineris must lie within or
above that range in order for pure, liquid water to exist there..

So, what is the atmospheric pressure at the bottom of Valles Marineris
at the point where the photo was taken?

Well, typical "surface" pressures on Mars, according to *The Facts on
File Dictionary of Astronomy* (pg. 268), are around 7 mb, which is
(7/1013)(760) = 5.25 mmHg, and so on the face of it liquid water should
not be able to exist there. However, at the location shown on the photo,
the bottom of Valles Marineris is about 5 km beneath the arbitrarily
chosen "surface" level. [See pg. 1, Adsorption water-driven processes on
Mars, D. Möhlmann, DLR-PF, Berlin, available at the ESA website.] Since
pressure increases as altitude decreases, the question is not whether
liquid water can exist at the artifically designated "surface" level on
Mars, but whether it can exist 5 km further down, under the higher
pressures that prevail at the bottom of Valles Marineris.

To try to answer that question, let's use the so called "barometric
pressure formula:"

P = P0e^(-Mg0z/RT)

In the above P0 is the pressure at the lower level, P is the pressure at
the upper level, e is the base of natural logarithms, M is the mass of 1
mole of atmosphere, g0 is the appropriate gravitational acceleration, z
is the vertical distance from the lower level to the upper level, R is
the molar gas constant, and T is the average absolute temperature in the
vertical column of atmosphere beginning at P0 and ending at the top of
the stratosphere (i.e., the bottom of the ionosphere).

Why the top of the stratosphere? Because the barometric formula only
calculates the effects of gravity on pressure. It is, in effect, a way
of determining the weight of a vertical column of atmosphere of unit
cross section at one level, based on knowledge of its weight at another
level and its average temperature. Since simple pooling of air molecules
under the influence of gravity ceases to be the dominant determinant of
pressure at the top of the stratosphere, the column of air to which the
barometric formula applies stops when the ionosphere is reached. That is
not to say that the air above the stratosphere, beginning with the
ionosphere, has no effect on pressures at lower levels. Rather it is to
say that the effects in question have very little to do with the
*weight* of the material, and a lot to do with such things as the solar
wind, solar radiation, magnetic field lines, etc.--things which the
barometric formula does not take into account. During the day, in fact,
the presence of upper atmosphere material has the effect of reducing the
ground level pressure rather than increasing it, which is the exact
opposite of what we would expect based on its weight. Thus to avoid
calculating a ground level pressure that is too high, I will ignore the
presence of that material.

We want to determine the pressure at the lower level, so we will solve
the barometric formula for P0, which gives the following:

P0 = P/e ^(-Mg0z/RT) (1

The various values on the right side are as follows:

(1) P = 7 mb, or 700 Pa.

(2) The value of e is 2.718....

(3) The Martian atmosphere is .95 CO2, .027 N2, .016 A, and .0015 O2, so
the mass of a mole of atmosphere is M = [.95(44) + .027(28) + .016(40) +
..0015(32)]/1000 = .04324 kg.

(4) Mars "surface" gravity is .37735849056603776 times that of Earth, so
g0 = 3.698 m/sec^2.

(5) The altitude difference is z = 5000 meters.

(6) The molar gas constant is R = 8.314 J/kg.

(7) To come up with a value for T, the average absolute temperature
below the ionosphere, requires a bit of work.

To begin, note that measurements by NASA's Mars Global Surveyor put the
top of the Martian stratosphere at about 93,000 meters. [See
http://agena.bu.edu/mars.htm.] That, therefore, will be the altitude of
the top of the column of atmosphere with which we are concerned. And the
altitude of the bottom of the column, for present purposes, will be 0
meters.

What we want is the average absolute temperature in that column of
atmosphere. To get it, we cannot simply take the middle altitude and
look up the temperature at that altitude, because the masses within the
column are not distributed evenly. The temperature of a mole of gas is T
= pv/R, and there are more moles per unit volume at the bottom of a
column of atmosphere than at the top, because the atmosphere gets
progressively thinner at higher altitudes. The average temperature, in
short, comes at the altitude of average density. Thus we will calculate
the average density, and then plug that value into the NASA Martian
Atmosphere Calculator (see
http://www.lerc.nasa.gov/WWW/K-12/airplane/atmosi.html) to determine the
temperature at that altitude. That will be the value of T that we seek.

According to the hydrostatic pressure formula, p = hdg. We will re-write
it as:

d = p/gh

d is the average density of the atmosphere in a column of unit cross
section stretching from the "surface" to the ionosphere.

p is the pressure at the bottom of the column--i.e., the surface
pressure of 700 Pa.

h in this case is the distance from ground level to the ionosphe
93,000 meters.

g is the gravitational acceleration on Mars, which is 3.698 m/sec^2.

The average density in the Martian atmosphere is therefore

d = p/gh = (700)/(3.698)(93000))

= .00203 kg/m^3, or .002, rounded.

Turning to the NASA calculator mentioned above and selecting "Mars" and
"metric units", we find that the density of the Martian atmosphere is
0.002 at an altitude of 20,433 meters, and that the temperature at that
altitude is -73 deg C. That, therefore, is the average temperature of
the portion of the Martian atmosphere which lies below the ionosphere.
The average absolute temperature in that region is therefore 273 - 73 =
200 K.

The estimated pressure at the bottom of Valles Marineris is therefore

P0 = 700/(2.718)^-(.04324)(3.698)(5000)/(8.314)(200), or

P0 = 1132.18 Pa, which is 11.3218 mb or 8.4942 mmHg.

Looking back at my vapor pressure tables for pure water, I find that
they are less than 8.4942 mmHg for temperatures up to 8.8 deg C. That
means pure water can exist in liquid form up to 8.8 deg C or 47.8 deg F,
at the location shown in the photo.

But, of course, any water flowing into the bottom of Valles Marineris
will without a doubt be mineral laden water from underground
hydrothermal sources. The salinity will be high, and as dissolved
minerals accumulate in water, its vapor pressure declines. Moreover, it
is a simple, linear relationship known as Raolt's law--to wit: the vapor
pressure of a solvent containing dissolved minerals is directly
proportional to the mole fraction of the solute in the solution, where
"mole fraction" is simply the number of moles of the substance (water,
in this case) divided by the total number of moles in the solution. Thus
if V0 is the vapor pressure of pure water at a given temperature, f is
the mole fraction of water in the solution, and V is the vapor pressure
of the solution, then according to Raolt's law, V = fV0.

Sea water, for example, contains 35 gm of dissolved salts for every kg
of water, with the salts being mostly NaCl. Let's simplify slightly and
assume the 35 gms are entirely NaCl. In that case, since the molecular
weight of NaCl is 58, the solution contains 35/58 = .6 mol, and, since
there are 1000 gms of H2O, which is 55.6 moles, it follows that the mole
fraction of H2O in sea water is 55.6/(55.6 + .6) = .989, and so for sea
water V = (.989)V0 as per the Raolt's law formula.

That, of course, means there is very little reduction in vapor pressure
when sea water is substituted for pure water. In fact, that only takes
us up to 8.9 deg C, where the vapor pressure drops to V = (.989)(8.551)
= 8.457 mmHg, which is just slightly less than the atmospheric pressure
of 8.49 mmHg. Thus if the water pouring into Valles Marineris were like
sea water on Earth, then it would remain liquid at temperatures up to
8.9 deg C, or 48 deg F.

However, sea water on Earth is not saturated with NaCl. In fact, 358 gms
of NaCl can be dissolved in 1 kg of water at 10 deg C (and more at
higher temperatures). That would be 358/58 = 6.17 moles. The 1000 gm of
H2O is 51 moles. Hence the mole fraction of water would be f =
55.6/(55.6 + 6.17) = .9. Result: V = (.9)V0. And that, based on another
look at the vapor pressure tables, is enough to permit liquid water to
exist up to 10.2 deg C, or about 50 deg F.

Other solutes, or multiple solutes, can take us even higher. Most
effective are salts with a low molecular weight and a high solubility,
so that the mole fraction of the solute jumps up, thereby reducing the
mole fraction of the solvent (water). Looking in my handbook again, I
see that the solubility (by interpolation) of LiCl at 12 deg C is 733 gm
in 1000 gm of H2O. Molecular weight of LiCl is 42, so that's 17.45
moles. The 1000 gm of H2O is 55.6 moles. Therefore the mole fraction of
water is 55.6/(55.6 + 17.45) = .761. Hence at 12 deg C we find that V =
(.761)(10.52) = 8.01 mmHg. And that works: with P = 8.49 mmHg and V =
8.0 mmHg, the water will remain liquid at 12 deg C, or 53.6 deg F.

Getting from 10 to 12 deg C by means of lithium chloride sounds like a
stretch, of course, but it could happen. It seems likely that the water
flowing into Valles Marineris is icemelt caused by heat emanating from
the magma chambers of the nearby Tharsis volcanos, and if the ultimate
source of the water is Mars' long since frozen ancient seas, it might
very well contain lots of dissolved salts, including LiCl. On Earth, for
example, it is estimated that there are 230 billion tons of lithium
chloride in sea water, but only 14 million tons on land. [See
http://202.221.217.59/print/news/nn0...040418a9.htm.] Moreover,
there is a process that would automatically raise all solutes to
saturation, given sufficient time. (See explanation further down.)

Anyway, regardless of how far above 10 deg C water can remain liquid in
Valles Marineris, it is a sure thing that pools of liquid water are a
real possibility there. Given the photo referenced earlier, showing the
fog and the apparent pools of blue water, it is my guess that Valles
Marineris was carved by underground icemelt flowing into the bottom of
the canyon, with the source of heat being the magma chamber under the
nearby Tharsis volcanos. I would suggest that geothermal heating from
magma near Valles Marineris melts buried ice from an ancient Martian
sea, and that liquid water then flows out into the bottom of the canyon.
Based on the above calcs, such water could remain liquid at least to 10
deg C and, arguably, to 12 deg C. Since solar heating would seldom push
the summer temperature above 10 deg C, and since water flows entering
the canyon from vents at the bottom would cool quickly by evaporation to
temperatures at which they would remain liquid, it follows that if
steady inflows of geothermally heated water are available at the bottom
of the canyon, pools of liquid water will exist there.

Interestingly, there is a photo of a portion of Reull Vallis, one of the
canyons feeding into Valles Marineris from the north, which appears to
show a lake of liquid water more than 100 km in length, and averaging 15
or 20 km in width. See
http://www.esa.int/export/SPECIALS/M...Z625WVD_1.html to
view this photo.

If you see nothing but bare rocks, then I suggest that you note the
following facts:

(1) If there is no wind or other source of disturbance, the surface of
water is as flat as a sheet of glass.

(2) If there are no suspended particulates, water is perfectly
transparent.

(3) The intrinsic color of water is blue, a fact that is revealed
progressively, as the water becomes deeper and deeper. [See
http://webexhibits.org/causesofcolor/5B.html.]

(4) The sky is not blue on Mars, so there is no opportunity for
reflection to make shallow water appear to be blue, as often happens on
Earth. Thus if water on Mars shows blue, it will be deep water only.

With those facts in mind, I suggest that you download the hi-res tiff
version of the above referenced photo and study it carefully. If you do,
you will note that a distinct water line is visible most of the way
around the lake, and that as the water gets deeper and deeper, its blue
coloration is progressively revealed.

I say that's a lake--a huge one, as a matter of fact.

Here is how such a lake would come into being:

(1) An upwelling of hot water from a deep geothermal source would spread
out on the bottom of the canyon.

(2) Atmospheric pressure at the bottom of the canyon would be roughly
8.49 mmHg and, if the air temperature were above roughly 10 to 12 deg C,
vaporization by boiling would promote rapid cooling of the water and
would increase its salinity.

(3) Over the eons, the salinity of the remaining water would be
progressively increased, each time the atmospheric temperature rose high
enough to cause a repetition of (2), above.

(4) Eventually, the salinity of the water, due to the buildup of
multiple solutes, would be so high that boiling would seldom occur.

Conclusion: the photo of the fog shows an episode where the air
temperature rose high enough to promote boiling; and the photo of the
lake in Reull Vallis shows the normal case, where the air temperature is
*not* high enough to promote boiling.

Interestingly, a continuation of such boiling episodes for millions or
billions of years would result in total saturation of the water, and
continued "salting out" of minerals onto the bottom. The result would be
a buildup of immense mineral deposits in the locations where the
repeated boiling episodes were occurring. The area beneath and around
the lake at Reull Vallis, for that reason, may very well contain some of
the richest surface mineral deposits in the Solar System.

There probably aren't any fish in the lake, however. :-)

--Mitchell Jones}***

Bob Clark


Robert Clark wrote:
Presentations from the First Mars Express conference held in February
are available he

First Mars Express Conference Presentations.
http://sci.esa.int/science-e/www/obj...objectid=36537

These reports are longer than the 2-page abstracts seen from the
Lunar
and Planetary Science Conference, some over 30 pages long.

A great image of dense fog in Valles Marineris is shown in this
report:

Reflectance of fog in Valles Marineris.
A. Inada
http://sci.esa.int/science-e/www/obj...objectid=36724

And this report has a beautiful full-color image of this very dense
fog:

Adsorption water driven processes on Mars.
D. Möhlmann
http://sci.esa.int/science-e/www/obj...objectid=36779

This article speculates on how adsorbed layers of water might be used
by microbes on Mars.

Valles Marineris is both low altitude and low latitude so should be
within the pressure and temperature range to permit liquid water for
this fog close to the surface.


cf.,

From: Robert Clark )
Subject: Supercooled liquid water can occur in clouds below 0 degrees
C.
Newsgroups: sci.astro, alt.sci.planetary, sci.geo.meteorology,
sci.geo.geology, sci.geo.mineralogy
Date: 2004-07-30 06:53:02 PST
http://groups.google.co.uk/groups?th=5bba314873613fde&


Bob Clark

In article ,
Mitchell Jones wrote:

In article ,
Mitchell Jones wrote:

[snip]

But, of course, any water flowing into the bottom of Valles Marineris
will without a doubt be mineral laden water from underground
hydrothermal sources. The salinity will be high, and as dissolved
minerals accumulate in water, its vapor pressure declines. Moreover, it
is a simple, linear relationship known as Raolt's law--to wit: the vapor
pressure of a solvent containing dissolved minerals is directly
proportional to the mole fraction of the solute in the solution, where
"mole fraction" is simply the number of moles of the substance (water,
in this case) divided by the total number of moles in the solution.

***{When I word something poorly in a post, I don't usually bother to
with a correction, provided that it is apparent from context that the
underlying thought was correct. However, the last sentence quoted above
sucks sooooooo much that I can't let it pass, even though my use of the
concept in the context was correct. The proper wording would be:

"Moreover, it is a simple, linear relationship known as Raolt's law--to
wit: the vapor pressure of a solution containing dissolved minerals is
directly proportional to the mole fraction of the solvent in the
solution, where "mole fraction" is simply the number of moles of the
solvent (water, in this case) divided by the total number of moles in
the solution."

So there you have it. :-)

--Mitchell Jones}***

[snip]

In article ,
Mitchell Jones wrote:

[snip]

Anyway, regardless of how far above 10 deg C water can remain liquid in
Valles Marineris, it is a sure thing that pools of liquid water are a
real possibility there. Given the photo referenced earlier, showing the
fog and the apparent pools of blue water, it is my guess that Valles
Marineris was carved by underground icemelt flowing into the bottom of
the canyon, with the source of heat being the magma chamber under the
nearby Tharsis volcanos. I would suggest that geothermal heating from
magma near Valles Marineris melts buried ice from an ancient Martian
sea, and that liquid water then flows out into the bottom of the canyon.
Based on the above calcs, such water could remain liquid at least to 10
deg C and, arguably, to 12 deg C. Since solar heating would seldom push
the summer temperature above 10 deg C, and since water flows entering
the canyon from vents at the bottom would cool quickly by evaporation to
temperatures at which they would remain liquid, it follows that if
steady inflows of geothermally heated water are available at the bottom
of the canyon, pools of liquid water will exist there.

Interestingly, there is a photo of a portion of Reull Vallis, one of the
canyons feeding into Valles Marineris from the north, which appears to
show a lake of liquid water more than 100 km in length, and averaging 15
or 20 km in width. See
http://www.esa.int/export/SPECIALS/M...Z625WVD_1.html to
view this photo.

If you see nothing but bare rocks, then I suggest that you note the
following facts:

(1) If there is no wind or other source of disturbance, the surface of
water is as flat as a sheet of glass.

(2) If there are no suspended particulates, water is perfectly
transparent.

(3) The intrinsic color of water is blue, a fact that is revealed
progressively, as the water becomes deeper and deeper. [See
http://webexhibits.org/causesofcolor/5B.html.]

(4) The sky is not blue on Mars, so there is no opportunity for
reflection to make shallow water appear to be blue, as often happens on
Earth. Thus if water on Mars shows blue, it will be deep water only.

With those facts in mind, I suggest that you download the hi-res tiff
version of the above referenced photo and study it carefully. If you do,
you will note that a distinct water line is visible most of the way
around the lake, and that as the water gets deeper and deeper, its blue
coloration is progressively revealed.

I say that's a lake--a huge one, as a matter of fact.

Here is how such a lake would come into being:

(1) An upwelling of hot water from a deep geothermal source would spread
out on the bottom of the canyon.

(2) Atmospheric pressure at the bottom of the canyon would be roughly
8.49 mmHg and, if the air temperature were above roughly 10 to 12 deg C,
vaporization by boiling would promote rapid cooling of the water and
would increase its salinity.

(3) Over the eons, the salinity of the remaining water would be
progressively increased, each time the atmospheric temperature rose high
enough to cause a repetition of (2), above.

(4) Eventually, the salinity of the water, due to the buildup of
multiple solutes, would be so high that boiling would seldom occur.

Conclusion: the photo of the fog shows an episode where the air
temperature rose high enough to promote boiling; and the photo of the
lake in Reull Vallis shows the normal case, where the air temperature is
*not* high enough to promote boiling.

Interestingly, a continuation of such boiling episodes for millions or
billions of years would result in total saturation of the water, and
continued "salting out" of minerals onto the bottom. The result would be
a buildup of immense mineral deposits in the locations where the
repeated boiling episodes were occurring. The area beneath and around
the lake at Reull Vallis, for that reason, may very well contain some of
the richest surface mineral deposits in the Solar System.

There probably aren't any fish in the lake, however. :-)

--Mitchell Jones}***

[snip]

[Note: the following analysis concerns the lake shown in the Mars photo
at the following link:
http://www.esa.int/export/SPECIALS/M...25WVD_1.html.]

According to the remarks beneath the photo, the area shown is 100 km
wide. Using that as my scale, I estimate that the lake in Reull Vallis
is at least 91 miles long, before it goes off of the photo (at both
ends). Its width at its narrowest point is 8.1 miles and at its widest
point is 38 miles. By way of contrast Lake Travis, a large lake in
Texas, is 60 miles long and 4.5 miles wide at its widest point. Thus the
Reull Vallis lake is huge!

How deep is it? Well, one strong hint is provided by the deep blue
fading to black along the bottom of the lake. As light passes through
clear water, it is attenuated by the water itself, which acts as an
absorbing medium. As the light passes deeper and deeper into the water,
it is attenuated in much the same way that atmospheric pressure is
attenuated by increasing altitude. The formula is as follows:

I = I0e^-ad

In the above, I is the intensity of the light after passing a distance d
through the absorbing medium, I0 is the intensity of the light when the
passage began, e is the base of natural logarithms, a is the absorption
coefficient of the light, and d is the distance of passage through the
medium.

Since the absorption coefficient varies in a very rough direct
proportion to the wavelength of the light, being very high for the long
wavelength (red) end of the spectrum, and very low for the short (blue)
end, we can calculate the depth where, say, 99% of the green light has
been absorbed, and that will be the depth beyond which, as a practical
matter, only blue light will reach the bottom. Hence the bottom will
appear very light blue when seen through water that is slightly deeper
than that, and progressively darker shades of blue as we go deeper
still, and, finally, when 99% of the blue light will itself have been
absorbed, only very dark blues will show, with black beyond. Since the
attenuation coefficient for the most energetic deep green light is .0162
per meter of distance travelled through the water, that is what we will
use. Using G to represent the intensity of the incoming green light, we
obtain:

..01G = Ge^-.0162d

..01 = e^-.0162d

ln .01 = -.0162d

-4.61 = -.0162d

d = 285 meters

So 99% of the deep green will be gone when the light has travelled
through 285 meters of water. Since the light comes from the sun, enters
the water, travels to the bottom, reflects, and then travels back to the
surface, the depth of the water when only a hint of green remains in the
blue will be d/2 = 230/2 = 142 meters.

At what depth will 99% of the deep blue be gone? Well, the absorption
coefficient of the most energetic deep blue light in pure water is
..00478 per meter of distance. Using B to represent the intensity of the
incoming blue light, we obtain:

..01B = Be^-.00478d

That leads to:

d = 964 meters

The lake depth is half of that, or 482 meters, as the deep blue fades
into black.

Conclusion: the lightest blue on the bottom of Reull Vallis Lake is at
depths of about 142 meters, and the darkest blues are at depths of about
482 meters. Below those levels, in the blackness, lies what are
doubtlessly lengthy passageways within a hydrothermal vent system,
leading eventually back to a magmatic heat source. That source could
either be a magma chamber close to the surface, with layers of rock
separating its top from buried ice, or it could be an active volcano
erupting periodically beneath a vast sheet of buried ice. The latter, in
my opinion, is far more likely, because such a postulate explains
virtually everything about Valles Marineris itself.

To elaborate, note that Valles Marineris begins near the Tharsis
volcanos, and slopes downhill away from them. If there were a vast ice
sheet from a frozen ancient sea, buried beneath surface accumulations of
rock and dust, and if an active volcano popped up under such an ice
sheet, its eruption would cause a collapse of the ice sheet at some
nearby point, wherever the overburden was weakest, and the overburden
would cave in on top of it. The result would be a lake of icemelt that
would boil in the low atmospheric pressure, melt nearby ice, and
gradually work its way downhill, collapsing the overburden as it did so.
Over hundreds of millions of years, such a process would form a vast
canyon system very much like Valles Marineris.

That, then, is my best guess as to what is going on he the bottom of
Valles Marineris is like the bottom of a teakettle which has repeatedly
been used to boil water for hundreds of millions of years, and has never
been cleaned. It contains a vast accumulation of "salted out" minerals,
and those minerals, in turn, rest on what was once the bottom of an
ancient sea. The walls of the canyon, by this reasoning, are going to
turn out to be mostly surface rocks that have fallen down as the ice
melted away beneath them, and, further back, behind the walls and under
the rocky overburden, lies the ice of the ancient sea itself. How thick
is that ice sheet? Several kilometers, I should think.

So there you have it! :-)

[Notes:

(1) I took my absorption coefficients from R. M. Pope and E. S. Fry,
"Absorption spectrum (380?700nm) of pure water. II. Integrating cavity
measurements," Appl. Opt., 36, 8710--8723,
(1997).

(2) The water in Reull Vallis Lake is not pure water. Unknown
concentrations of unknown solutes are dissolved in it. Hence the above
calculations are only estimates.]

--Mitchell Jones

Thanks for your extraordinary message, one of the best ones
I have seen in this newsgroup for years.

NASA is brain dead.
We must somehow work around it.


ES

Hello Mitchell,

The Reull Vallis Lake images are compelling to say the least.
What I don't understand is why the caption does not discuss the blue
color. I would seem that it is such a contrast from the normal color
range observed one could not look at it with out saying "whats that
about ?" yet not one peep from the Mars groups. (I am at steward
observatory across the way from LPL.) We are sitting around the control
room at one of our observatories asking questions like..
Is it due to false color processing ? or what else would be blue ?
Observations at different sun angles would help and what about radar data ?
One would think that this is the story of the year (or more) if was true.

When I get back down to UA I will ask a Mars head.

What fun

Dan






Mitchell Jones wrote:
In article ,
Mitchell Jones wrote:

[snip]



--Mitchell Jones

These photos are all courtesy of ESA and their orbiter, dumbass.


wrote in message
oups.com...
NASA is brain dead.
We must somehow work around it.


ES