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Water Ice On Mars
cathector sends along a story from SpaceWeather.com on the discovery of water ice on Mars.
"Scientists have figured out the mysterious white substance unearthed by NASA's Phoenix lander on Mars. It's frozen water. The breakthrough came last week when Phoenix's stereo camera caught the substance in the act of disappearing. Bathed in martian sunlight for four days, the white substance sublimated — i.e., it transformed from solid to gas without passing through the liquid state. This is how water behaves on Mars.... Some readers have asked, how do we know the white substance is not frozen CO2 (dry ice) instead of frozen water? Answer: Phoenix's landing site is too warm for dry ice. The average daily temperature is about -70 F while dry ice requires temperatures lower than about -109 F." The animated GIF showing the ice sublimating is pretty nice too.
http://science.slashdot.org/article.pl?sid=08/06/20/026241
First against the wall when the revolution comes
That animation is actually cut off. The main sublimation that was observed is below the frame of that picture. There's a better one here, where you can actually see the small chunks farther down disappearing completely.
It was at the bottom of a trench. Plus, wind doesn't selecticely blow white rocks away while letting the rest of the scene untouched. Plus, you can also see some white areas at the end of the trench getting smaller.
It's ice. Definitely.
"It's too bad that stupidity isn't painful." - Anton LaVey
escape velocity on mars is 5.027 km/s, and water vapor will slowly move out of mars because of its high rms velocity. So, the answer is "no"
Doesn't really need to be under low air pressure, if ice is in the presence of low vapor-pressure it will sublimate (see icecube tray in your freezer).
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WHO ATE MY BREAKFAST PANTS?
Indeed it does, and it's probably better explained using a triple point diagram:
http://www.chemistrydaily.com/chemistry/Image:Phase-diag.png
On earth (at higher pressures), increasing temperature goes from the solid, to liquid, and then to gas phases (the triple-point in the middle is at zero degress celcius)
The lower atmospheric pressure on Mars (~1% of sea-level earth pressure) means that you go straight from solid to gas. In fact, the liquid part is actually impossible (IANAChemist) unless you increase the pressure sufficiently.
I'm sure that quote was with regard to the conditions of Mars.
You are also correct to assume that Martian pressure is nowhere near what is required for room-temperature dry ice. In fact it's about 1% that of earth's atmosphere. More reading here.
Well, back to rejecting software patent applications.
Here's the problem: We still don't know conclusively. Yes, we have observations which are highly suggestive, but we don't have a chemical composition of the substance, so we don't know for sure.
Science is a hard mistress; she demands proof before making such claims.
Mod me down with all of your hatred and your journey towards the dark side will be complete!
Not only that, but Phoenix has a little weather station on board called the Telltale project. And if you look at this page you can see the weather reports for where Phoenix is on a sol by sol basis. None of them show windy conditions, although it looks like there is data missing for a few sols.
http://www.rootstrikers.org/
water sublimation doesn't need to be exotic; it happens in your freezer all the time.
you know how ice cubes gradually lose their sharp edges and finally become just little puddle-shaped lumps in the bottom of the ice try ? that's sublimation too.
Here
How to read them
I feel that a great disservice was done to a lot of us early on with a simplistic view of the usual three phases of matter.
And yes, you're right. That is part of the explanation.
To quote wikipedia: This can occur if the atmospheric pressure exerted on the substance is too low to stop the molecules from escaping from the solid state.
Atmospheric pressure is not as important as the partial pressure of the substance at its surface. That is, in this case, the vapour pressure of water which is practically zero on Mars. Therefore water, if it is not locked down in crystalline form, cannot exist in liquid form because it cannot form an equilibrium with its surroundings to form a 'triple point' (solid/liquid/vapour phase temperature).
It also depends, as far as I understand, on the interaction between molecules of the substance. If it is too weak, the range of temperatures at which the substance can be liquid is narrow (or practically zero). It's a fairly wide range for water, though.
I didn't study the topic beyond that and it was years ago.
PS. Iodine is another substance that sublimates.
Do it yourself, because no one else will do it yourself. [beta blockade 10-17 Feb]
Yes, still not cold enough as far as I can tell given this phase diagram and these temperatures and pressures.
Were that I say, pancakes?
U.S needs to upgrade it's standards. A good start would to move from Fahrenheit to Celsius. After that you can move over to the metric system.
-70 F is -56 C
-109 F is -78 C
Conversion done with Google.
Calculate your own conversion to attempt-by-the-French-to-regain-relevance-on-the-world-stage units.
Gee, if metric is an attempt by France to regain relevance, they've succeeded everywhere bar America. Continuing use of imperial units must be attempt-by-the-Americans-to-deny-progress-and-sanity.Metric is the global standard. Get over it.
Man who leaps off cliff jumps to conclusion.
I thought this Wired quote about why the water sublimates on Mars is interesting:
"Just like dry ice does here on Earth, water ice goes from solid to gas when the pressure is below 6.1 millibars and it gets heated (like it does in the Martian sun). It can also go straight from solid to gas above 6.1 millibars when the vapor pressure (amount of water vapor in the air) is low enough. This is because the molecules of water in solid form and gas form are not at equilibrium."
http://blog.wired.com/wiredscience/2008/06/answering-mars.html
ZuluPad, the wiki notepad on crack
All materials sublimate. The liquid phase doesn't exist beneath a substance's triple point, so at pressures beneath that level temperature increases cause the material to go directly from solid to gaseous (sublimate). http://en.wikipedia.org/wiki/Image:Phase-diag2.svga has a good picture of what we're thinking about.
Relax I just want some peanuts.