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.
In other news, NASA announced today that a manned mission to Mars is planned to retreive the newly found ice in time for the 2012 Kentucky Derby. NASA plans to upstage Woodford Reserve's famous $1000 Mint Julep at the race with its own $3,000,000 version of the traditional cocktail. While plans are still being firmed up, the beverage will reportedly come in a limited edition collector's glass.
Pardon my total ignorance of the subject, but does this mean that it might occasionally snow on mars? Or would the environment be too different to allow it?
No, martian air is way too dry to form snow. There is water in the athmosphere, but IIRC it is something like a layer 1mm thick if all the water would condense on the ground. What happens is that some of that water freezes to/in the ground if it gets cold enough.
What I learned from following the press conferences online, is that since mars doesn't have a large moon, the axis of rotation changes much more than earth does, so if it is directed towards the sun, the ice could actually melt.
Pardon my total ignorance of the subject, but does this mean that it might occasionally snow on mars? Or would the environment be too different to allow it?
The area the lander in is covered by ice during the winter so we are going to find the answer to your question quite soon.
If I remember my chemistry classes correctly (there is a high chance I don't), water would do this under lower air pressure, I think. Correct me if I'm wrong, I just thought some kind of explanation would be better than "because it's on Mars".
Pretty much anything can sublimate under the proper conditions. But when you say "a white solid that sublimates at -70 degrees F and martian surface pressure and is found in macroscopic quantities naturally" you narrow down the field quite a bit. In this case, to exactly one reasonable possibility.
by Anonymous Coward
on Sunday June 22 2008, @07:43PM (#23898635)
Pretty much anything can sublimate under the proper conditions. But when you say "a white solid that sublimates at -70 degrees F and martian surface pressure and is found in macroscopic quantities naturally" you narrow down the field quite a bit. In this case, to exactly one reasonable possibility.
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.
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 [wikipedia.org] has a good picture of what we're thinking about.
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).
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.
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.
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 [arizona.edu], where you can actually see the small chunks farther down disappearing completely.
I've noticed that almost all of the news headlines covering this are qualified statements like "Lander finds water on Mars, according to scientists". As if they're afraid to actually say something straightforward like "Water found on Mars" and they have to make it clear that they're just reporting what someone else is saying (with the implication that maybe they don't really believe it). At the same time they seem to have no problem with other headlines like "Celebrity Arrested Drunk" without the need to qualify it as "Celebrity Arrested Drunk According To Police" etc.
Maybe it's just me, but I mind it a bit irksome that so many big news outlets seem so detached from any sort of science reporting these days.
They would be better off sending their own fucking probe than subtracting 32 and multiplying by 4/9. I'm not sure what units those are, but certainly not Celsius.
Could we have this important information in units used by, I don't know, the rest of the world?
Hah! With this announcement, NASA has predicated that Fahrenheit is now used on the surface of two worlds, thus re-establishing its dominance over that other temperature unit which is only used in part of one world. We will wrest control of this universe back from you metric heathens, even if we have to do it one planet at a time!
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.
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.
Finding water was one of the key goals of the Phoenix mission.
That is a bizarre statement. Large quantities of ice have been observed in numerous ways already. Even the Viking lander observed water frost directly in the 1970's:
Not only is that ice, it may actually be an outflow.
What makes the results from Phoenix exciting is that the actual experiments that Phoenix is supposed to perform depend on having landed on ice. But finding ice somewhere on Mars is not a surprise.
Yes, water ice on Mars is nothing new. That's why they went there. They could not have another failed mission, could they? Before Phoenix there was Opportunity. Why? The NASA-funded mineralogical neophytes spent our money looking for liquid water where they saw widespread hematite...coarse grained grey hematite. Fe2O3...no water in its structure! On Earth, in the banded iron formations that are BILLIONS of years old, that is a metamorphic mineral. It did not form in liquid water! Its PRECURSOR minerals (goethite; ferrihydrite; lepidocrocite) did form in water. Using hematite as a "beacon" for liquid water would be like using anthracite coal as a beacon for a coal swamp or a piece of chinaware as a beacon for a kaolin mine. Now we have a mission that is the equivalent of finding sand in the Sahara Desert? They KNEW that there was water ice there...for years. Big deal? Unbelievable spin! If they actually find anything relevant to life on Mars one needs to inquire... Why didn't they go there in the first place? Why did they waste our money landing in a billion year old metamorphic landscape? Even the face-saving hematite "blueberries" are a joke when placed into context with the remote data used to select that landing site...platy coarse-grained hematite.
First, I think the best evidence so far that this is water is not this picture, but the fact that the Mars Orbiter's spectrometer determined that that is was a lot of hydrogen in the ground near the poles.
That some white stuff vanishes is poor evidence. They need to get the white stuff in an oven and test it.
Let's assume it is water. What really puzzles me is how clean the water is. It is covered with what would make a dirty mud if it ever melted together. Also on earth, you never have clean water if you have flash floods like what you see as a result of a volcanic eruption or meteroid impact. You only have clean water/ice in snow and still lakes/oceans. This implies: 1. The ice has not melted after the dust blew over it.(A long time) 2. It used to be a lake/ocean or snow
So the purity of the ice might be a bigger discovery than the fact that it is ice there.
there's a number of geological processes that can concentrate water like this
in areas on earth where a lot of freezing and thawing occurs on earth, rocks get concentrated neatly in rings according to size, as if someone sorted them
i'm not saying this process is anything like why the ice is so pure on mars, what i am saying is that there are plenty of natural processes out there that concentrate materials in orders that, contraintuitively, seem like it took intelligent concentration, but are in fact totally natural
i won't even begin to speculate what processes on mars could do this, but i wouldn't be surprised if someone more knowledgeable than me could describe such a natural mechanism for ice purification on mars
So these two frames [spaceweather.com] were taken four days apart while the sublimation was taking place. My question would be - where are the rest of the frames? Does this lander really only "look around" every few days?
It would be nice to see it at even a 1-day resolution and get a 4-frame animation of the process. Those lumps should be seen to get smaller and vanish.
Not that I'm complaining, this is still very cool (no pun intended).
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."
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.
Not only that, but Phoenix has a little weather station on board called the Telltale project [marslab.dk]. And if you look at this page [space.gc.ca] 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.
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. [wikipedia.org]
Perhaps next mission they should take along some sugar. Put it out and see if it 'sublimates' as well.
Memo to all Enforcers: By order of the Council of Elders, anyone caught consuming the sweet, sweet bait near the robotic invader from the blue planet is to have his gelsacs summarily pierced. Signed, K'Breel
A similar experiment was recently conducted to determine the existence of life in Congress. A large pile of money was left sitting out which sublimated while votes accreted; thereby proving the existence of life in Congress. It is still up for debate how long before intelligent life is found in Congress.
$3,000,000 mint juleps at next year's derby (Score:4, Funny)
In other news, NASA announced today that a manned mission to Mars is planned to retreive the newly found ice in time for the 2012 Kentucky Derby. NASA plans to upstage Woodford Reserve's famous $1000 Mint Julep at the race with its own $3,000,000 version of the traditional cocktail. While plans are still being firmed up, the beverage will reportedly come in a limited edition collector's glass.
Snow (Score:5, Interesting)
Re:Snow (Score:5, Interesting)
No, martian air is way too dry to form snow. There is water in the athmosphere, but IIRC it is something like a layer 1mm thick if all the water would condense on the ground. What happens is that some of that water freezes to/in the ground if it gets cold enough.
What I learned from following the press conferences online, is that since mars doesn't have a large moon, the axis of rotation changes much more than earth does, so if it is directed towards the sun, the ice could actually melt.
Parent
Re:Snow (Score:5, Interesting)
Parent
Dupe from Thursday (Score:5, Informative)
Water sublimating (Score:5, Interesting)
Re:Water sublimating (Score:5, Interesting)
Is water the only material that can sublimate? If not, why should we be so sure this has to be water just because we want it to be?
Parent
Re:Water sublimating (Score:5, Insightful)
Parent
I know (Score:5, Funny)
Yep, Vodka.
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Re:I know (Score:5, Funny)
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Re:Water sublimating (Score:5, Informative)
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.
Parent
Re:Water sublimating (Score:4, Informative)
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 [wikipedia.org] has a good picture of what we're thinking about.
Parent
Re:Water sublimating (Score:5, Informative)
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).
Parent
Re:Water sublimating (Score:4, Informative)
Indeed it does, and it's probably better explained using a triple point diagram:
http://www.chemistrydaily.com/chemistry/Image:Phase-diag.png [chemistrydaily.com]
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.
Parent
Re:Water sublimating (Score:5, Informative)
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.
Parent
Better picture (Score:5, Informative)
Martian ice is really big news, folks! (Score:5, Funny)
Re:Martian ice is really big news, folks! (Score:5, Funny)
Sorry - it's a Scotch joke.
Parent
Re:Martian ice is really big news, folks! (Score:4, Funny)
Please call it by its proper name, would you?
Martch.
Parent
Interesting press coverage of this. (Score:5, Insightful)
I've noticed that almost all of the news headlines covering this are qualified statements like "Lander finds water on Mars, according to scientists". As if they're afraid to actually say something straightforward like "Water found on Mars" and they have to make it clear that they're just reporting what someone else is saying (with the implication that maybe they don't really believe it). At the same time they seem to have no problem with other headlines like "Celebrity Arrested Drunk" without the need to qualify it as "Celebrity Arrested Drunk According To Police" etc.
Maybe it's just me, but I mind it a bit irksome that so many big news outlets seem so detached from any sort of science reporting these days.
G.
In Other News... (Score:5, Funny)
More at 8.
Parent
average daily temperature (Score:5, Insightful)
Could we have this important information in units used by, I don't know, the rest of the world?
Re:average daily temperature (Score:5, Funny)
Send your own fucking probe if you can't be bothered to subtract 32 and multiply by 4/9.
Parent
Re:average daily temperature (Score:5, Funny)
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Re:average daily temperature (Score:5, Funny)
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Re:average daily temperature (Score:5, Informative)
Calculate your own conversion to attempt-by-the-French-to-regain-relevance-on-the-world-stage units.
Metric is the global standard. Get over it.
Parent
Re:average daily temperature (Score:5, Funny)
Long live imperial units! I say, if God had wanted us to use metric, He would have given us ten fingers! ...
oh, crap.
Parent
One Problem: (Score:5, Informative)
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.
ice on Mars is nothing new (Score:5, Insightful)
Finding water was one of the key goals of the Phoenix mission.
That is a bizarre statement. Large quantities of ice have been observed in numerous ways already. Even the Viking lander observed water frost directly in the 1970's:
http://en.wikipedia.org/wiki/Viking_2 [wikipedia.org]
http://www.solarviews.com/cap/mars/frost.htm [solarviews.com]
That frost sublimated just like this ice did.
Here are other observations:
http://science.nasa.gov/headlines/y2002/28may_marsice.htm [nasa.gov]
Here you can see a frozen crater lake:
http://esamultimedia.esa.int/images/marsexpress/210-010705-1343-6-co-01-CraterIce_H.jpg [esa.int]
http://www.esa.int/SPECIALS/Mars_Express/SEMGKA808BE_0.html [esa.int]
Not only is that ice, it may actually be an outflow.
What makes the results from Phoenix exciting is that the actual experiments that Phoenix is supposed to perform depend on having landed on ice. But finding ice somewhere on Mars is not a surprise.
Re:ice on Mars is nothing new (Score:4, Interesting)
Parent
How come the water is so white/clean? (Score:5, Interesting)
First, I think the best evidence so far that this is water is not this picture, but the fact that the Mars Orbiter's spectrometer determined that that is was a lot of hydrogen in the ground near the poles.
That some white stuff vanishes is poor evidence. They need to get the white stuff in an oven and test it.
Let's assume it is water.
What really puzzles me is how clean the water is. It is covered with what would make a dirty mud if it ever melted together. Also on earth, you never have clean water if you have flash floods like what you see as a result of a volcanic eruption or meteroid impact. You only have clean water/ice in snow and still lakes/oceans.
This implies:
1. The ice has not melted after the dust blew over it.(A long time)
2. It used to be a lake/ocean or snow
So the purity of the ice might be a bigger discovery than the fact that it is ice there.
not necessarily amazing (Score:5, Interesting)
there's a number of geological processes that can concentrate water like this
in areas on earth where a lot of freezing and thawing occurs on earth, rocks get concentrated neatly in rings according to size, as if someone sorted them
i'm not saying this process is anything like why the ice is so pure on mars, what i am saying is that there are plenty of natural processes out there that concentrate materials in orders that, contraintuitively, seem like it took intelligent concentration, but are in fact totally natural
i won't even begin to speculate what processes on mars could do this, but i wouldn't be surprised if someone more knowledgeable than me could describe such a natural mechanism for ice purification on mars
Parent
Four days apart (Score:4, Insightful)
So these two frames [spaceweather.com] were taken four days apart while the sublimation was taking place. My question would be - where are the rest of the frames? Does this lander really only "look around" every few days?
It would be nice to see it at even a 1-day resolution and get a 4-frame animation of the process. Those lumps should be seen to get smaller and vanish.
Not that I'm complaining, this is still very cool (no pun intended).
Standards.... (Score:5, Informative)
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.
Re:Wow (Score:5, Funny)
You're absolutelly right, all we need now is some Martian Whisky and the social lives of any future human expedition is well and truly sorted out.
Parent
Re:Wow (Score:5, Funny)
> Hopefully they are right about it.
Of course they're right about it, they have solid photographic evidence. [nasa.gov]
Parent
Re:Wow (Score:5, Funny)
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Re:Wow (Score:5, Informative)
"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 [wired.com]
Parent
Re:Wow - not (Score:5, Insightful)
There is a fair bit of difference between believing and knowing!
Parent
Re:Wind? (Score:5, Informative)
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.
Parent
Re:Wind? (Score:5, Informative)
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Re:Wind? (Score:5, Insightful)
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Re:Wind? (Score:5, Funny)
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Re:Wind? (Score:5, Insightful)
Neither, because NASA only hires smart people.
Parent
Re:Wind? (Score:4, Funny)
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Re:Stupid terraforming.. (Score:5, Informative)
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Re:What about the pressure? (Score:4, Informative)
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. [wikipedia.org]
Parent
Re:Life on Mars (Score:5, Funny)
Perhaps next mission they should take along some sugar. Put it out and see if it 'sublimates' as well.
By order of the Council of Elders, anyone caught consuming the sweet, sweet bait near the robotic invader from the blue planet is to have his gelsacs summarily pierced.
Signed,
K'Breel
Parent
Re:Life on Mars (Score:4, Funny)
Parent
Re:could be CO2? (Score:4, Informative)
Yes, still not cold enough as far as I can tell given this phase diagram [fsnet.co.uk] and these temperatures and pressures [wikipedia.org].
Parent