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AZgazer
2004-May-17, 05:36 AM
I was under the impressoin that we are searching for evidence of water on Mars... I was just cruising for facts and thought I'd look at some fast Mars facts and Wikipedia says Mars has ice caps (http://en.wikipedia.org/wiki/Mars_(planet)). Did we just really miss something on the caps? or is the site wrong? or am I just really confused?

Kaptain K
2004-May-17, 05:53 AM
That Mars has ice caps has been known for some time. What we are looking for is signs of liquid water either present or past.

AZgazer
2004-May-17, 06:17 AM
OK, maybe I am missing something then... how would water get to ice without having been liquid?

Water has 3 states, correct? Gas, liquid and Solid. I just can't figure out how you could have ice caps without the water having been liquid.

Sorry, I am not trying to be argumentative or trivial, the fact that we know of water in ice and it was never liquid just seems really confusing to me.

kucharek
2004-May-17, 07:59 AM
The keyword is sublimation. Below a certain pressure (7mbar, IIRC), water immediadetly turns from ice into vapor and vice versa. Just like we know under our normal atmospheric condictions carbon dioxide behaves.

Harald

AZgazer
2004-May-17, 08:21 AM
Kucharek thank you, I have been pulling my hair out trying to figure out how this is possible. One thing I did do was search for sublimination and I wasn't able to get any decent sites with information. I went through about 60 google matches on it and all I could find was a few places with "substances going from gas to solid without liquid form or vice cersa" type stuff, does anyone know of a decent science/chemistry site with more information on it?

Tranquility
2004-May-17, 09:59 AM
Here (http://wine1.sb.fsu.edu/chm1045/notes/Forces/Phase/Forces06.htm) is a page that shows phase diagrams and explains briefly sublimation and when it would occur.

JonClarke
2004-May-17, 10:08 AM
Water vapour can likewise go to ice without going through the liquid phase by freezing directly onto a cold surface.

Jon

LTC8K6
2004-May-17, 11:30 AM
Like a high altitude contrail from an airplane.

LTC8K6
2004-May-17, 11:36 AM
I wouldn't trust Wikipedia because anybody can add anything to it.

If you scroll down to the bottom of the page, you'll see that you have the ability to edit the page yourself, along with a disclaimer link.


Wikipedia is an online open-content encyclopedia, that is, a voluntary association of individuals and groups who are developing a common resource of human knowledge. Its structure allows any individual with an Internet connection and World Wide Web browser to alter the content found here. Therefore, please be advised that nothing found here has necessarily been reviewed by professionals who are knowledgeable in the particular areas of expertise necessary to provide you with complete, accurate or reliable information about any subject in Wikipedia.

AZgazer
2004-May-17, 02:20 PM
Excellent responses, thanks to everyone. I had never seen Wikipedia until I came here and have seen it used as a source often and never questioned, so I took it as a reliable source. The fact that is editable makes a lot of sense now. Yesterday I submitted a link from Wikipedia to a medical board I am a member of asking some of the MD's to correct some grossly inaccurate information.

tlbs101
2004-May-17, 06:58 PM
I added a single paragraph to the article on Albuquerque, NM. and even though what I added was simple and obvious (to me), I still spent over an hour doing chekcing and double checking on my very simple fact, then I spent another 15 minutes on the grammer and spelling, etc.

I took that task (of adding to Wikepedia) very seriously, but I still see your point, because I realize not everyone takes the time to verify what they might consider 'fact'.

Planetside
2004-May-17, 07:06 PM
The pictures of the ice caps look like it was once running water. Like it froze during a whirl pool or something.

I remember seeing the frozen ice caps images days before NASA announced the major discovery of "water once on mars". I was looking at that image wondering what the heck?

01101001
2004-May-17, 08:49 PM
The pictures of the ice caps look like it was once running water. Like it froze during a whirl pool or something.
Looks can be deceiving.


I remember seeing the frozen ice caps images days before NASA announced the major discovery of "water once on mars". I was looking at that image wondering what the heck?
Others wondered, too. One came up with a better explanation (http://www.space.com/scienceastronomy/mars_spirals_040325.html):


The tilted planet causes ice on one side of a crack to heat and vaporize, deepening and widening the crack. Then the water vapor hits the shady, colder side of the growing canyon and refreezes. ... "The logarithmic pattern occurs because the troughs migrate at a slower rate near the poles because it is colder there and melting takes place more slowly, Pelletier said. "This causes them to 'bunch up' nearer towards the poles."

Maksutov
2004-May-18, 04:04 AM
I had to correct an error in a Wikipedia article which had the 100 inch telescope on Mount Wilson listed as being a refractor.

It's good for general information and links, but look out for the details. :wink:

AstroSmurf
2004-May-18, 09:38 AM
The quality of the articles on Wikipedia can vary wildly; I've seen some that never would be acceptible for a dead-tree encyclopedia. However, I've also found immensely detailed and informative entries, so it evens out. The more frequently an entry is accessed, the better its quality will be.

RGClark
2004-May-18, 06:28 PM
That Mars has ice caps has been known for some time. What we are looking for is signs of liquid water either present or past.

Here's my bet for where liquid water will be found on Mars:

NASA SP-441: VIKING ORBITER VIEWS OF MARS
------------------------------------------------------------
- THE ATMOSPHERE -
"Early Morning Clouds in the Tharsis Montes and Valles Marineris
Region. Ascraeus Mons and Pavonis Mons are prominently displayed in
this mosaic, and dense cloud blankets cling to their northern slopes.
High cirrus clouds lie to the west of Tharsis, and waves are visible
in the clouds surrounding the peaks. Bands of clouds appearing to
have a cellular structure extend north from the canyon, and the areas
within and immediately surrounding the chasm exhibit water-ice fogs.
[211-5049; 5S, 105W]"
"Early Morning Surface Fog. The presence of morning fogs in some
crater and channel bottoms is a Viking discovery with possible
implications for the future biological exploration of Mars. These
early morning views of the Memnonia region were taken one-half hour
apart using a violet filter to enhance the contrast of the
condensates. The areas marked by arrows are noticeably brighter in
the later picture. The fogs indicate specific spots where water is
exchanged, probably on a daily cycle, between the surface and the
atmosphere. The surface and lower air layers in this region become
unusually cold at night because of the thermal properties of the
surface. When the surface warms in the morning, it seems that a small
amount of water vapor-estimated to be about one-millionth of a meter
thick if liquefied is driven off; this vapor recondenses in the
atmosphere, which warms more slowly, to form a ground fog of ice
particles. [P17487; 13S,147 W]"
"Early Morning Clouds in Noctis Labyrinthus. Condensate clouds are
seen here in early morning in the canyons of Labyrinthus Noctis,
which lies at the western end of the equatorial Valles Marineris
system. This picture, which covers about 90 000 km2, was made by
combining three frames of the same field taken through violet, green,
and red filters. Although these clouds lie mainly down inside the
canyons, they evidently extend above the walls and spill over some of
the surrounding plateau. Like most condensate clouds in the Martian
troposphere, they are believed to be composed of water-ice crystals.
[P18114, 9S, 95W]"
http://history.nasa.gov/SP-441/ch12.htm

See also the large size images of Noctis on this page:

Clouds in Noctis Labyrinthis.
http://planetscapes.com/solar/cap/mars/noctis.htm

Note that Noctis Labyrinthus is both low latitude and low altitude. So both temperature and pressure can be in the range to permit liquid water during Summer daytime hours.
These fogs close to the surface could become liquid during those times. Remember visible fogs and clouds consist either of ice or liquid, not just water vapor which is invisible.


Bob Clark