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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.
There is wind, however it apparently didn't move anything else in the pictures. Also, the wind wouldn't be very strong since the atmosphere is so thin.
On Mars, between 7 and 10 millibar.
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!
CO2 sublimes on earth of course, and many other substances do under different conditions. Per the summary, we know it could not be frozen CO2.
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/
It's 1% of Earth's atmospheric pressure. At that point there is no water, only solid and gas. And the sublimation point is a lot lower because of the lower pressure. (Less pressure = less molecules keeping the other molecules tightly packed)
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]
But you're right, either way the dissociated hydrogen is way lighter.
a,e,i,o,u and sometimes w and y (at be if of up cwm by)
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.
That a lot of the people here see dry ice, white and solid like the stuff found on mars, and the fact that dry ice subliminates in our atmosphere, and come up with the idea that the white stuff must be solid CO2 and not water. Of course this is completely fallacious logic, as the pressure and temp in the area make it physicaly impossible for CO2 to be a solid (if temp/pressure data is correct)....
I've read Slashdot for the last 5 years, and now I start posting... Go figure
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
PI'm just flabbergasted that the ice could exist so close to the surface without sublimating purely from solar warming of the soil.
The soil on Mars is cold enough (say -50 C) to keep ice from sublimating below a certain depth. From the pictures I would say that depth is 50-100 mm.http://michaelsmith.id.au
Two things I guess. First, the scoop and rasp allows the other tools that they brought like cameras to be used. An auger just creates a small diameter hole in the ground. Second, the auger and any support instruments would probably add considerable power and weight demands to the mission. They don't need that equipment in order to do useful research.
If I understand correctly, the water is blowing away.. just not as crystals. It is blowing away as discreet water molecules much like evaporation. The crystals gain energy from the sun and a little from the impact of the atmospheric gases and then the water molecules lift from the crystal lattice and suspend in the atmospheric gas matrix.
If you visualize everything as tiny versions of the colored balls in a child's play pit, you will notice that each type of ball (atom) has a different weight and tends to stratify. With enough energy added to the ball, it will then de-stratify and lift into the active matrix of the atmosphere.
Codifex Maximus ~ In search of... a shorter sig.
The Phoenix lander is an international project including instruments from many non-US contributors. There is little justification for using Fahrenheit in this article, because these numbers do not relate to human intuition -- fucking cold is fucking cold in Celsius and Fahrenheit.
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.
Make that two worlds and one moon.
I'm sorry, but this really annoys me. What does the escape velocity have to do with the rms temperature of vapor? Assuming a Maxwell-Boltzmann distribution (which we certainly can at these temperatures) we have that the rms speed is (3RT/M)^1/2, M being the molar weight. If this were to be the 5*10^6m/s you're claiming it is, it would mean that T=1.8*10^10 K. Clearly, that's not the temperature of Mars.
Then again, I guess that fancy words sound smarter, and more +5 Informative.