Water at Martian south pole

On Thu, 18 Mar 2004, Jacques van Oene wrote:

Thanks to ESA's Mars Express, we now know that Mars has vast fields of
perennial water ice, stretching out from the south pole of the Red Planet.

Read mo
http://www.esa.int/SPECIALS/Mars_Exp...KEX5WRD_0.html


Did you notice where they state that late summer time at Mars'
south poles tempeture is 130 Celsius. Surely this is in error.
What is the correct tempeture?

William Elliot wrote in
:

On Thu, 18 Mar 2004, Jacques van Oene wrote:

Thanks to ESA's Mars Express, we now know that Mars has vast fields
of perennial water ice, stretching out from the south pole of the Red
Planet.

Read mo
http://www.esa.int/SPECIALS/Mars_Exp...KEX5WRD_0.html


Did you notice where they state that late summer time at Mars'
south poles tempeture is 130 Celsius. Surely this is in error.
What is the correct tempeture?


the article states
(quoted in part)
"when it was late summer for the Martian southern hemisphere and
temperatures would be at their highest. Even so, that is probably only –130
degrees Celsius and the ice that Mars Express has observed is a permanent
feature of this location"

Minus 130C sounds about right. This is about 143K, a bit hotter than liquid
nitrogen.


Maybe you missed the (minus) sign?


P.S.
Just what happens when the ambient temerature is *far* below the freezing
point of the main constituent of the atmosphere? A continuous snowing out
of the atmosphere, with the winds etc.. that would go along with that?

On Sun, 21 Mar 2004, Marvin wrote:

William Elliot wrote in
On Thu, 18 Mar 2004, Jacques van Oene wrote:

(quoted in part)
"when it was late summer for the Martian southern hemisphere and
temperatures would be at their highest. Even so, that is probably only –130
degrees Celsius and the ice that Mars Express has observed is a permanent
feature of this location"

Minus 130C sounds about right. This is about 143K, a bit hotter than liquid
nitrogen.

Maybe you missed the (minus) sign?

Yes, it wasn't low bit ascii, so it didn't show up with Lynx.
Pine shows some character in your post, but not a minus sign.

P.S.
Just what happens when the ambient temerature is *far* below the freezing
point of the main constituent of the atmosphere? A continuous snowing out
of the atmosphere, with the winds etc.. that would go along with that?

Lots of dry ice. What is freezing point of CO2 ? Way above the freezing
point of N2. So I'll guess -100 C.

What do you have in mind? sci.space.news reports indicate not enuf CO2 in
South Pole to make much effect upon atmosphere pressure, hence
temperature. You query if the dust storms are driven by the south polar
winds?

William Elliot wrote:
On Thu, 18 Mar 2004, Jacques van Oene wrote:

Thanks to ESA's Mars Express, we now know that Mars has vast fields of
perennial water ice, stretching out from the south pole of the Red Planet.

Read mo
http://www.esa.int/SPECIALS/Mars_Exp...KEX5WRD_0.html


Did you notice where they state that late summer time at Mars'
south poles tempeture is 130 Celsius. Surely this is in error.
What is the correct tempeture?

No they don't, they state its -130C

--
Sander

+++ Out of cheese error +++

William Elliot wrote in
:

On Sun, 21 Mar 2004, Marvin wrote:

William Elliot wrote in
On Thu, 18 Mar 2004, Jacques van Oene wrote:

(quoted in part)
"when it was late summer for the Martian southern hemisphere and
temperatures would be at their highest. Even so, that is probably
only –130 degrees Celsius and the ice that Mars Express has observed
is a permanent feature of this location"

Minus 130C sounds about right. This is about 143K, a bit hotter than
liquid nitrogen.

Maybe you missed the (minus) sign?

Yes, it wasn't low bit ascii, so it didn't show up with Lynx.
Pine shows some character in your post, but not a minus sign.
Cute. I think the problem is that the original site used a non-standard
character for the minus sign. I directly copy-pasted the text, and while it
appears *fine* in my editing window, the main display window of my
newsreader pukes the character. Probably the same thing that hit you in the
first place.


P.S.
Just what happens when the ambient temerature is *far* below the
freezing point of the main constituent of the atmosphere? A
continuous snowing out of the atmosphere, with the winds etc.. that
would go along with that?

Lots of dry ice. What is freezing point of CO2 ? Way above the
freezing point of N2. So I'll guess -100 C.

What do you have in mind? sci.space.news reports indicate not enuf
CO2 in South Pole to make much effect upon atmosphere pressure, hence
temperature. You query if the dust storms are driven by the south
polar winds?

My point being:
The 'air' on Mars is basically pure CO2.
The ambient temperature is FAR below the freezing point of CO2, therefore
there is a strong force trying to get that gaseous CO2 to sublimate into
dry ice.

CO2 sublimates at about -78c, well above the ambient temperature. The heat
of fusion is a significant but smallish 571j/g
The vapour pressure of solid CO2 at -130celcius is virtually zero.
One would expect the atmospheric CO2 to snow out at relatively great rates.
This would of course deplete the local atmosphere over the poles, causing
extreme low pressure zones. Even considering how very thin the Mars air
density is, i would expect this to trigger lots of wind as the denser areas
try to fill this. Expect the reverse to happen during a hot spell, as the
ground CO2 would evaporate, filling the local atmosphere to much higher
than usual densities. The normal atmospheric content of mars is only that
of about 4 cm of dry ice, (in gas form of course). Evaporate another 4cm
and you have just doubled the local air pressure.

In article , Marvin wrote:
The 'air' on Mars is basically pure CO2.
The ambient temperature is FAR below the freezing point of CO2...

Bear in mind that "the freezing point" isn't a unique number -- it depends
on pressure. At an ambient pressure of a few millibars, the freezing point
of CO2 is nearly 50K colder than at 1atm.

The vapour pressure of solid CO2 at -130celcius is virtually zero.

Actually, it's about 3 millibars according to the Matheson Gas Data Book
(6th ed), which would be insignificant on Earth but is highly significant
on Mars, especially in highland areas like the South Pole.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

From: Henry Spencer
Newsgroups: sci.space.policy
Subject: Water at Martian south pole

Marvin wrote:
The 'air' on Mars is basically pure CO2.
The ambient temperature is FAR below the freezing point of CO2...
therefore there is a strong force trying to get that gaseous CO2
to sublimate into dry ice.

Bear in mind that "the freezing point" isn't a unique number -- it
depends on pressure. At an ambient pressure of a few millibars, the
freezing point of CO2 is nearly 50K colder than at 1atm.
That would put the freezing point of Martian CO2 at about -130, the
recorded summer south pole temperature, which explains why the cap shrinks
and expands with Mars' seasons. Indeed, if freezing was -80 C at 3 mbars,
then the equilibrium condition would be no measurable atmosphere.

At 3 mbar, what's freezing point of H2O ? That is
quantitatively, how permanent are the s.pole ice fields?

The vapour pressure of solid CO2 at -130celcius is virtually zero.
Actually, it's about 3 millibars according to the Matheson Gas Data
Book (6th ed), which would be insignificant on Earth but is highly
significant on Mars, especially in highland areas like the South
Pole.

The normal atmospheric content of mars is only that of about
4 cm of dry ice, (in gas form of course). Evaporate another 4cm
and you have just doubled the local air pressure.
That would compute were the atmosphere in an inclosed chamber which it
isn't. More ground level pressure, comes only of added CO2 mass above.

Solving Mars's Polar-Ice Puzzle, 2/25/03
SkyandTelescope.com/news/current/article_881_1.asp
While the polar caps likely contain enough water to form a global ocean
about 20 meters deep, there may only be enough dry ice in storage to raise
the atmospheric pressure by a minuscule 0.36 millibar -- just 5% above its
current value.

Which would put Mars atmospheric pressure at about 7 mbar.
Do they mean ground level pressure at some imaginary sea level?

----

In article ,
William Elliot wrote:
Bear in mind that "the freezing point" isn't a unique number -- it
depends on pressure. At an ambient pressure of a few millibars, the
freezing point of CO2 is nearly 50K colder than at 1atm.

At 3 mbar, what's freezing point of H2O ? That is
quantitatively, how permanent are the s.pole ice fields?

Pretty permanent. :-) At 3mbar -- which is below the triple-point
pressure of water, so liquid is not present, only solid and gas -- the
freezing point is -8.2degC. I don't have tables going down to -130,
but at -98, the vapor pressure of water is about 0.00002mbar. Which is
why the atmosphere of Mars is pretty dry...

"While the polar caps likely contain enough water to form a global ocean
about 20 meters deep, there may only be enough dry ice in storage to raise
the atmospheric pressure by a minuscule 0.36 millibar -- just 5% above its
current value."

Which would put Mars atmospheric pressure at about 7 mbar.

It averages about 6mbar, but that depends a lot on elevation and I seem to
recall some seasonal variation as well.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

Marvin wrote:
The 'air' on Mars is basically pure CO2.
The ambient temperature is FAR below the freezing point of CO2...

And the ambient temperature on earth is below the boiling point of
water. Often below the freezing point. Nevertheless, there is plenty
of water vapor in earth's atmosphere.

The freezing point defines the temperature above which you won't find
the solid, not the temperature below which you won't find the gas.
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.

On Mon, 22 Mar 2004, William Elliot wrote:
| Bear in mind that "the freezing point" isn't a unique number -- it
| depends on pressure. At an ambient pressure of a few millibars, the
| freezing point of CO2 is nearly 50K colder than at 1atm.
|
|That would put the freezing point of Martian CO2 at about -130, the
|recorded summer south pole temperature, which explains why the cap shrinks
|and expands with Mars' seasons. Indeed, if freezing was -80 C at 3 mbars,
|then the equilibrium condition would be no measurable atmosphere.
|
|At 3 mbar, what's freezing point of H2O ? That is
|quantitatively, how permanent are the s.pole ice fields?

How high is the polar ice cap, anyway? If it is over 500 feet thick,
what is the pressure under it? Is it thick enough to make water
crystals liquefy?