New Study Claims Mars Dry for 4 Billion Years

Today on the Web there was an item at space.com by Senior Science
Writer Robert Roy Britt, announcing the results of a study due to
appear in the July 22 issue of the journal Science, in which Caltech
graduate student David Shuster and Asst. Prof. Benjamin Weiss suggest
that Mars hasn't had "large areas of freestanding water for four
billion years", but don't rule out "pockets of isolated water in
geothermal springs for periods of time".

The study is based upon argon decay analysis of the remaining argon
content of seven meteorites "known to have arrived from Mars after
millions of years in space". The study relies on a formula for argon
decay that varies with temperature. "Any way we look at it, these
rocks have been very cold for a very long time," says Shuster.

As of this posting, the 7/22/05 issue of Science is not yet available
at its online site www.sciencemag.org .

Offhand, there seem to be a number of assumptions to be justified.
Whether the study does so successfully remains to be seen, though the
fact that these represent elementary issues suggests that they wouldn't
be overlooked.

First, how is it known that the rocks weren't in space for merely
"millions of years" but perhaps for billions of years? If they were
thrust into space as the result of a cataclysmic event four billion
years ago, and have been floating in space during the intervening time,
wouldn't the study be invalidated by the fact that space is cold?

Second, what were the climate patterns on Mars up until the time these
rocks became spaceborn? Could they have originated in a part of Mars
that was "very cold" without implicating the same climate for all the
rest of the planet?

Third, what were the original argon levels in these rocks, and how is
this known? If volcanic, other geological, atmospheric, or even
biological processes resulted in a different argon ratio than expected,
could this alter the validity of the study?

Other questions come to mind, but these are the primary ones that
occured to me while reading the media coverage of the study.

Mark Adkins

Dear msadkins04:

wrote in message
ups.com...
....
First, how is it known that the rocks weren't in space for
merely
"millions of years" but perhaps for billions of years? If they
were
thrust into space as the result of a cataclysmic event four
billion
years ago, and have been floating in space during the
intervening
time, wouldn't the study be invalidated by the fact that space
is
cold?

The fact that these meteorites were in ice a few (to several)
hundreds of thousands of years old, indicates that they were
floating in space for most of the time.

Space isn't cold, but the balance between a sink temperature of
3K, and the Sun at 6000K, will achieve a net temperature likely
close to something between Earth and Mars... *on average*.
Atmosphere only lowers that amplitude of the swings... with
little or no effect on the average.

David A. Smith

On a sunny day (21 Jul 2005 13:14:33 -0700) it happened
wrote in . com:

Today on the Web there was an item at space.com by Senior Science
Writer Robert Roy Britt, announcing the results of a study due to
appear in the July 22 issue of the journal Science, in which Caltech
graduate student David Shuster and Asst. Prof. Benjamin Weiss suggest
that Mars hasn't had "large areas of freestanding water for four
billion years", but don't rule out "pockets of isolated water in
geothermal springs for periods of time".
Like here for example:
http://panteltje.com/panteltje/space...olordetail.jpg
from
http://panteltje.com/panteltje/space...lake2color.jpg
from
http://panteltje.com/panteltje/space...22_reull_v.jpg
from
http://sci.esa.int/science-e/www/obj...objectid=34508
all in COLOR.
These springs? I do not think so, but who knows.

On a sunny day (21 Jul 2005 13:14:33 -0700) it happened

wrote in . com:

Today on the Web there was an item at space.com by Senior Science
Writer Robert Roy Britt, announcing the results of a study due to
appear in the July 22 issue of the journal Science, in which Caltech
graduate student David Shuster and Asst. Prof. Benjamin Weiss suggest
that Mars hasn't had "large areas of freestanding water for four
billion years", but don't rule out "pockets of isolated water in
geothermal springs for periods of time".
Like here for example:
http://panteltje.com/panteltje/space...olordetail.jpg
from
http://panteltje.com/panteltje/space...lake2color.jpg
from
http://panteltje.com/panteltje/space...22_reull_v.jpg
from
http://sci.esa.int/science-e/www/obj...objectid=34508
all in COLOR.
These springs? I do not think so, but who knows.

N:dlzc D:aol T:com (dlzc) wrote:
Dear msadkins04:

wrote in message
ups.com...
...
First, how is it known that the rocks weren't in space for
merely "millions of years" but perhaps for billions of years? If they
were thrust into space as the result of a cataclysmic event four
billion years ago, and have been floating in space during the
intervening time, wouldn't the study be invalidated by the fact that space
is cold?

The fact that these meteorites were in ice a few (to several)
hundreds of thousands of years old, indicates that they were
floating in space for most of the time.

Space isn't cold, but the balance between a sink temperature of
3K, and the Sun at 6000K, will achieve a net temperature likely
close to something between Earth and Mars... *on average*.
Atmosphere only lowers that amplitude of the swings... with
little or no effect on the average.

David A. Smith

Dear Mr. Smith,

If space isn't "cold", in the colloquial sense of this term, and with
respect to the area of space occupied by these rocks during their time
in space, how is it that these rocks were still *in ice*? Also, if the
rocks were "known to have arrived from Mars after millions of years in
space" then how is it that the ice they were encased in was only "a few
(to several) hundreds of thousands of years old"? (Note that the
newest ice would be closest to the surface and therefore melt away
first.) Assuming, for the sake of argument, that some of the ice was
burned off by atmospheric friction during meteoric entry, or even by
heat from the sun while floating through space, my point remains
unaltered. Finally, I fail to see how your reply is at all responsive
to my question re billions vs. millions of years (how long they were in
space) and what the answer implies for the validity of the study
results.

Mark Adkins

Dear msadkins04:

wrote in message
oups.com...
N:dlzc D:aol T:com (dlzc) wrote:
Dear msadkins04:

wrote in message
ups.com...
...
First, how is it known that the rocks weren't in space for
merely "millions of years" but perhaps for billions of
years?
If they were thrust into space as the result of a
cataclysmic
event four billion years ago, and have been floating in
space during the intervening time, wouldn't the study be
invalidated by the fact that space is cold?

The fact that these meteorites were in ice a few (to several)
hundreds of thousands of years old, indicates that they were
floating in space for most of the time.

Space isn't cold, but the balance between a sink temperature
of 3K, and the Sun at 6000K, will achieve a net temperature
likely close to something between Earth and Mars... *on
average*. Atmosphere only lowers that amplitude of the
swings... with little or no effect on the average.

If space isn't "cold", in the colloquial sense of this term,
and
with respect to the area of space occupied by these rocks
during their time in space, how is it that these rocks were
still *in ice*?

Because they were "dug" out of ice that was not very old
(compared to billions of years). Namely at the poles of the
Earth.

Also, if the
rocks were "known to have arrived from Mars after millions
of years in space" then how is it that the ice they were
encased in was only "a few (to several) hundreds of
thousands of years old"? (Note that the newest ice would
be closest to the surface and therefore melt away
first.)

The ice record is continuous, and ages beyond the level the
meteorites were discovered at. That couldn't happen through
successive freeze-thaw.

Assuming, for the sake of argument, that some of the
ice was burned off by atmospheric friction during meteoric
entry, or even by heat from the sun while floating through
space, my point remains unaltered.

*All* the ice was "burned off". Then it was covered with snow.
Then it was packed into a glacier.

Finally, I fail to see how your reply is at all responsive
to my question re billions vs. millions of years (how long
they were in space) and what the answer implies for the
validity of the study results.

It only addresses your misunderstanding about the "coldness of
space". See above where you said:
QUOTE
wouldn't the study be invalidated by the fact that space
is cold?
END QUOTE

Note that I said nothing to your other three (?) points, since I
did not feel I could contribute rationally. Your questions there
appear to be good ones to me.

David A. Smith

Dear Mr. Smith,

First, let me note that the July 22nd issue of Science is available at
its Website, www.sciencemag.org and that the full text of the article
in question is now available there to the general public. (Click on
"see current issue" then on "research articles" then on the Mars
temperature by Shuster et al.)

The rocks are said to have been ejected into space some eleven million
years ago, and that assertion is based upon cosmic-ray exposure
testing. That opens an entirely different can of worms, so let's stick
to the point of contention/confusion we've been haggling over.

You say that the area of space that the rocks spent their time in
(while in space) varies in temperature between 3 K and 6000 K, and that
"on average" the temperature is somewhere between that of Mars and that
of Earth. That's quite a variation -- anything up to 273.15 K being at
or below freezing -- and it isn't clear to me how meaningful that
average is, because it may merely be mathematical and of no actual
bearing upon temperatures the meteorites have been exposed to.

I suppose I'm confused, if that's the case, because the media
description of the article said: (A) that argon decay analysis -- which
is temperature sensitive -- permitted the study authors to determine
that the near-surface temperature of Mars hasn't, within the last four
billion years, been significantly above the current cold temperature (
0 degrees Celsius); (B) in support of this thesis, quoted one of the
study's authors as saying "However you look at it, these rocks have
been very cold for a very long time".

OK, you say that space, at least within the area of our Solar System
where these rocks are said to have floated around for millions of
years, isn't cold. Then, I don't see how these rocks could have been
"very cold for a very long time". If the study's authors were merely
referring to a period of a few hundred thousand years during which time
they were (you've said) buried in the Earth's polar regions, how would
this be relevant to the argon-decay testing thesis? The idea, I take
it, is that if these rocks have remained cold, very little argon has
been released, and argon levels in the rocks are comparable to what
they were when on Mars. On the other hand, if they were floating
around in space at temperatures above freezing for millions of years,
they haven't been "very cold for a very long time". Could variations
in their temperature during that period skew the argon-decay analysis
in ways that would invalidate the study's conclusion?

Now that I've read your reply, I'd be curious to know why these rocks
fell at the Earth's poles, and what that might imply about their
orbital trajectories in the period immediately before capture by the
Earth.

Mark Adkins

"m" == msadkins04 writes:

m Today on the Web there was an item at space.com by Senior Science
m Writer Robert Roy Britt, announcing the results of a study due to
m appear in the July 22 issue of the journal Science, in which
m Caltech graduate student David Shuster and Asst. Prof. Benjamin
m Weiss suggest that Mars hasn't had "large areas of freestanding
m water for four billion years", but don't rule out "pockets of
m isolated water in geothermal springs for periods of time".

Some of your comments may be outdated, now that the actual article has
appeared, but just in case that isn't so....

m The study is based upon argon decay analysis of the remaining argon
m content of seven meteorites "known to have arrived from Mars after
m millions of years in space". The study relies on a formula for
m argon decay that varies with temperature. [...]

Not decay, diffusion. (Of course, this confusion may have been
generated by the space.com article.) Decay implies a nuclear
reaction, which shouldn't be affected by temperature (at least not at
the temperatures of interest here).

Diffusion, OTOH, can be affected by temperature. The hotter a rock
is, the easier it is for gasses to diffuse through it.


m Offhand, there seem to be a number of assumptions to be justified.
m Whether the study does so successfully remains to be seen, though
m the fact that these represent elementary issues suggests that they
m wouldn't be overlooked.

Always be careful about assessing the validity of a scientific paper
based on its press coverage.

m First, how is it known that the rocks weren't in space for merely
m "millions of years" but perhaps for billions of years? [...]

Cosmic ray exposure. There is a host of material about this on the
Web, but, simply put, the longer a rock is in space, the more cosmic
rays to which it is exposed, and the more isotopes are produced in the
rock from nuclear reactions.

m Second, what were the climate patterns on Mars up until the time
m these rocks became spaceborn? Could they have originated in a part
m of Mars that was "very cold" without implicating the same climate
m for all the rest of the planet?

I suppose that is the case. Of course, as one would sample more and
more meteorites, this case would become less and less likely.

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Joseph Lazio wrote:
"m" == msadkins04 writes:

m The study is based upon argon decay analysis of the remaining argon
m content of seven meteorites "known to have arrived from Mars after
m millions of years in space". The study relies on a formula for
m argon decay that varies with temperature. [...]

Not decay, diffusion. (Of course, this confusion may have been
generated by the space.com article.) Decay implies a nuclear
reaction, which shouldn't be affected by temperature (at least not at
the temperatures of interest here).

Diffusion, OTOH, can be affected by temperature. The hotter a rock
is, the easier it is for gasses to diffuse through it.

Yes, the term "decay" appeared in the space.com summarizing the (then
unpublished) Science article. I thought it was a bit odd, but assumed
(wrongly, as it turned out) that the senior science writer at a media
outlet devoted to astronomical issues would get it right, and supposed
that it was some obscure but proper nomenclature.


m Offhand, there seem to be a number of assumptions to be justified.
m Whether the study does so successfully remains to be seen, though
m the fact that these represent elementary issues suggests that they
m wouldn't be overlooked.

Always be careful about assessing the validity of a scientific paper
based on its press coverage.

Excellent point.


m First, how is it known that the rocks weren't in space for merely
m "millions of years" but perhaps for billions of years? [...]

Cosmic ray exposure. There is a host of material about this on the
Web, but, simply put, the longer a rock is in space, the more cosmic
rays to which it is exposed, and the more isotopes are produced in the
rock from nuclear reactions.

Might they have floated through space for billions of years without
appreciable cosmic ray exposure because they were interior portions of
much larger Martian rocks? By the time a meteorite reaches the surface
of the Earth, it is likely to be much smaller than before it entered
the atmosphere. Furthermore, it is not unthinkable that during several
billion years of drifting through the solar system, in belts to which
meteoritic debris is drawn, that collisions may have occurred. Now,
here are two alternative scenarios, which incidentally are not mutually
exclusive: (a) Eleven million years ago the rocks in question were
liberated, in space collisions, from much larger rocks of which they
were interior pieces, and which had previously limited their cosmic ray
exposure; (b) These rocks are the remaining core pieces of a larger
rock (or multiple larger rocks) whose exterior portions were burned
away (and/or broke away) during entry into Earth's atmosphere and/or
upon impact, and the appearance of eleven million years worth of cosmic
ray exposure is really the result of a much longer exposure shielded by
the layers of rock surrounding them for most of their space travel.


m Second, what were the climate patterns on Mars up until the time
m these rocks became spaceborn? Could they have originated in a part
m of Mars that was "very cold" without implicating the same climate
m for all the rest of the planet?

I suppose that is the case. Of course, as one would sample more and
more meteorites, this case would become less and less likely.

Well, at the present time, I believe something like seven rocks were
sampled. Even assuming the cosmic ray dating method is appropriate,
that number is not statistically significant, particularly if they were
found in the same area (on Earth), since such a grouping might be
interpreted as evidence that they shared a common orbit and hence,
perhaps, a common origin.


--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
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Mark Adkins

"m" == msadkins04 writes:

m Joseph Lazio wrote:
"m" == msadkins04 writes:

m The study is based upon argon decay analysis of the remaining argon
m content of seven meteorites "known to have arrived from Mars after
m millions of years in space". [...]

m First, how is it known that the rocks weren't in space for merely
m "millions of years" but perhaps for billions of years?

Cosmic ray exposure. There is a host of material about this on
the Web, but, simply put, the longer a rock is in space, the more
cosmic rays to which it is exposed, and the more isotopes are
produced in the rock from nuclear reactions.

m Might they have floated through space for billions of years without
m appreciable cosmic ray exposure because they were interior portions
m of much larger Martian rocks? By the time a meteorite reaches the
m surface of the Earth, it is likely to be much smaller than before
m it entered the atmosphere.

Umm, why?

m Furthermore, it is not unthinkable that during several billion
m years of drifting through the solar system, in belts to which
m meteoritic debris is drawn, that collisions may have occurred.
m Now, here are two alternative scenarios, which incidentally are not
m mutually exclusive: (a) Eleven million years ago the rocks in
m question were liberated, in space collisions, from much larger
m rocks of which they were interior pieces, and which had previously
m limited their cosmic ray exposure; (b) These rocks are the
m remaining core pieces of a larger rock (...) whose exterior
m portions were burned away (...) during entry into Earth's
m atmosphere and/or upon impact, and the appearance of eleven million
m years worth of cosmic ray exposure is really the result of a much
m longer exposure shielded by the layers of rock surrounding them for
m most of their space travel.

I guess in order to demonstrate that either of these are superior to
the currently stated scenario (of an 11-million year exposure because
that's how long the rock had been in space) you have to determine the
following:

1) What's the cross-section for collisions? A collision would be an
easy way to grind up a rock. However, the likelihood of a rock
being in a collision depends upon its size. So how big does a rock
have to be before it is likely to be in an appreciable collision
during the lifetime of the solar system?

2) What's the size of rock have to be before cosmic-ray exposure ages
are affected? Your alternate scenarios depend upon
"self-shielding," the ability of outer layers of a rock to
"protect" inner layers. How big does a rock have to be for that to
be the case?

--
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