Under the "Further evidence for Martian liquid equatorial water" thread Slinted posted:
That link contains this passage:Originally Posted by slinted
"It seemed difficult to explain the existence of such a quantity of ice so nearby the surface : more than half a milimeter of water frost is currently laying down during autumn and winter at high latitudes. Nevertheless, this ice cap sublimates completely at the end of spring. This ice was proposed to be resulted from a slow diffusion of water between the Martian regolith and the atmosphere but the in situ measurements of porosity from Viking spacecrafts have shown that the regolith can not contain any ice with such a concentration. The study directed by the researchers from Paris Observatory and IPSL suggests that *the solution may come from astronomical forcing of Martian climates."
My opinion is that the alternative explanation that the Viking Mars landers underestimated the amount of water in the Martian regolith is not given sufficient consideration. I've written about this fact in a post to sci.astro:
==========================================
From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re: Mars Odyssey lecture and water on Mars.
Newsgroups: sci.astro, alt.sci.planetary, rec.arts.sf.science, sci.astro.seti
Date: 2002-05-12 06:59:39 PST
henry@spsystems.net (Henry Spencer) wrote in message news:<GvzFuz.MrJ@spsystems.net>...
> In article <832ea96d.0205111957.69851900@posting.google.co m>,
> Robert Clark <rgregoryclark@yahoo.com> wrote:
> >...describes a discrepancy between the Viking lander GCMS data and the
> >data returned by the Gamma Ray spectrometer on Mars Odyssey.
>
> My first reaction is that there are so many differences in how the two
> measurements were taken that this may not mean a whole lot. For one
> thing, if I recall correctly, the GRS penetrates rather more deeply.
>
> Not to be overlooked, also, is that the two measurements are a quarter of
> a century apart... and as the MGS images of the south-pole area recently
> revealed, Mars is changing slowly in poorly-understood ways.
>
> >According to the March 1st news conference the GRS was described as
> >indicating "several percent" water content in the Martian soil...
>
> Uh, that was in the *south pole* region (south of 60degS). That's not
> where the Vikings were.
>
> >DiGregorio mentions the GCMS NEVER GOT AN INDICATION THAT SAMPLES
> >WERE DELIVERED TO THE CHAMBER. This indicates that either there was a
> >flaw in the mechanism detecting sample delivery or the GCMS never got
> >a large enough sample to register.
>
> The former. There was definitely a sample in the chamber when the GCMS
> runs were actually made -- an empty chamber would not have produced those
> results. (In fact, the guys who had been sweating over the lack of a
> "chamber full" signal were greatly relieved when they saw that.)
Thanks for your as usual insightful comments.
If you note in the lecture Gibbs shows in fact a distribution of water
in areas including the Northern hemishere. This happens about 47
minutes into the lecture. If you are using the RealOne player you
should be able to scroll to this portion of the lecture. Also, recall
late last year the GRS team released preliminary reports of large
amounts of water in the northern hemisphere as well:
New Signs of Water on Mars Create Hope of Great Discovery.
By Leonard David,Senior Space Writer and Robert Roy Britt,Senior
Science Writer
posted: 09:07 am ET, 14 December 2001
"The quantity of hydrogen detected was so startling -- suggesting a
huge concentration relative to what Feldman saw with a similar
instrument on Lunar Prospector, which surveyed the Moon -- that
researchers may task Odyssey to begin mapping crustal water ice during
the first week January, Garvin said."
http://www.space.com/scienceastronom...en_011214.html
Gibbs did offer the possibility that GRS was seeing water deeper down
but note that the spectrographic data would be of water at the
surface. I should say though in that article I cited by Yen et.al.
they did discuss one article by Houck et.al. that is consistent with
the 1 to 2% figure of the GCMS:
Houck, J.R., J.B. Pollack, C. Sagan, D. Schaack, and J.A. Decker Jr.,
High Altitude Infrared Spectroscopic Evidence for Bound Water on Mars,
Icarus, 18, 470-480, 1973.
In regards to the GCMS never receiving a sample full indication note
that in the reports on the instrument it is acknowledged it has to be
assumed that a sample of correct size was delivered:
"The are two positions to which any of the ovens
can be moved in any sequence. The load position is
directly under the sampling system, which delivers about
1-2 cm^3 of surface material that after having been
ground is passed through a 0.3 mm sieve. A mechanical
poker pushes the material through a funnel into the oven.
This operation is timed in such a manner that the filling
of the oven is complete with any of the terrestrial test
soils (including finely ground basalt, commonly referred
to as 'lunar nominal'). However, there is no sensor
measuring the final level or completeness of the fulling
operation. Thus one has to assume that the oven is filled
to capacity, i.e., approximately 60 mm^3 of surface
material is being analyzed."
The Search for Organic Substances and Inorganic Volatile
Compounds in the Surface of Mars,
Jour. Geophys. Res., vol. 82, no. 28, September 30, 1977, p. 4642.
Pictures and a description of the sample collectors are given in an
online NASA publication:
ON MARS
Exploration of the Red Planet 1958-1978.
"The first soil samples were acquired on sol 8, 28
July. Four samples were dug, with the first being
deposited into the biology instrument distributor
assembly, the next two into the GCMS processor, and
the fourth into the funnel of the x-ray fluorescence
spectrometer. All the commands were successfully
executed, but there was no positive indication that the
gas chromatograph-mass spectrometer processor
had been properly filled. A second acquisition attempt
still did not provide a "sample level detector `full'
indication". The sampler system, having completed its
programmed sequences in a normal manner, parked the boom
as planned. On Earth, the lander performance specialists
began to analyze the possible causes of the anomaly: (1)
insufficient sample acquired in the collector head
because the same sample collection
site had also been used for the biology sample; (2)
insufficient time allowed for the sample to pass from the
funnel through the sample grinding section and then
through the fine (300-micrometer) sieve into the metering
cavity of the instrument; (3) grinder stirring spring not
contacting the sieve; or (4) sample-level-detector
circuit faulty. Since the "level-full" detector
consisted of a very fine wire stretched across the cavity
to which the sample material was
delivered, it was also possible that it had broken when
the soil was dropped into the funnel."
Ch. 11-5 SCIENCE ON MARS
http://www.hq.nasa.gov/office/pao/Hi...12/ch11-5.html
Note as well that the sample full indicators for the biology
experiments were exactly of the same type yet they did get sample full
indications at both lander sites. The only difference between the
sample delivery to the biology experiments and to the GCMS was that
the GCMS used a much smaller sieving grid (0.3 mm) *before* being
passed through the sample full indicator. The obvious conclusion to
draw is that the small sieving grid somehow prevented full samples
from being delivered, for example if there were several large grains,
bigger than 300 microns, that blocked the grid.
If there were large amounts of water in the sample then that would be
taken as an indication of a sample being delivered by the GCMS
detecting that water. That is, the water that was detected might mean
a full sample was delivered which contained low amounts of water, the
accepted interpretation, or it could mean an unexpectedly small sample
was delivered that contained large amounts of water. Keep in mind
again, since the sample full indicator never registered, it is
impossible to know for sure what was the size of the sample delivered.
Bob Clark
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