Ice Found On Mars: Wet or Dry?

[Warren Platts]

Martian Ice Discovered Beneath Red Soil, NASA Says (Update2)

June 20 (Bloomberg) -- The existence of ice on Mars was confirmed today by NASA scientists, the first time frozen water has been sampled on another planet. Water in liquid form is an essential ingredient for life.

Whitish, dice-sized chunks, which were dug from the rocky red soil and warmed in the sun, vanished four days after the National Aeronautics and Space Administration's Phoenix probe dug them up June 15. They confirm what NASA satellites have suggested for years: Frozen water exists several centimeters beneath Mars's surface.

. . .

The University of Arizona team ruled out the possibility that the material might be dry ice or salt.

Salt wouldn't vaporize, and dry ice, or frozen carbon dioxide, exists at much cooler temperatures than found at the Phoenix landing site.

The ground temperature at Phoenix's location at this time of year falls to as cold as minus 112 degrees Fahrenheit (minus 80 degrees Celsius) at night and can warm up to minus 25 degrees Fahrenheit during the day.

I think they are reaching, and will be forced to eat crow. It's dry ice, and it didn't sublimate before because it was covered with dirt before. That's why you wrap dry ice in newspaper before you put it in your cooler to keep your ice cream frozen--the newspaper reduces the rate of sublimation. Same principle.

Sure the pressure's much less on Mars, but the phase diagram at below zero temperatures is very steep, so that the sublimation temperature of CO₂ on Mars isn't that much different than on Earth.

[aurora]

So where do you think the hydrogen is? Obviously, dry ice has no hydrogen.

[Warren Platts]

So where do you think the hydrogen is? Obviously, dry ice has no hydrogen.

Either you're joking or English isn't your first language, and that's OK.

Dry Ice
–noun Chemistry, Trademark.
the solid form of carbon dioxide, which sublimes at −109.26°F (−78.48°C) and is used chiefly as a refrigerant.

from Dictionary.com

[aurora]

Either you're joking or English isn't your first language, and that's OK.

English is my first language. And I am not joking.

I was asking you to explain, if they have found dry ice as you said it is, where the hydrogen is. Hydrogen has been detected near the surface over the entire region.

So if it is dry ice, where is the hydrogen?

[Warren Platts]

English is my first language. And I am not joking.

I was asking you to explain, if they have found dry ice as you said it is, where the hydrogen is. Hydrogen has been detected near the surface over the entire region.

So if it is dry ice, where is the hydrogen?

And Warren seems to not know (or not understand question) about hydrogen detected by Mars Odyssey on poles - exactly where Phoenix is.

The orbiter actually measured gamma rays, not hydrogen itself, and other things besides water have hydrogen, e.g., methane (CH₄) and ammonia (NH₃), both common ingredients in the solar system.

[JonClarke]

The orbiter actually measured gamma rays, not hydrogen itself, and other things besides water have hydrogen, e.g., methane (CH₄) and ammonia (NH₃), both common ingredients in the solar system.

Methane is sold only at -185.2 degrees. That is way too cold for Mars. The only way that methane can be in the solid state at maartian temperatures is as a water-methane clathrate, which has six molecules of water to one of methane.

Ammonia is not solid about -77 degrees. Maybe clathrates are posssible, but these are going to be predominantly water ice again.

If there were abundant methane and ammonia clathrates about you would expect there to be traces of these compunds in the atmsophere. If present they are so in vanishingly small quantities, so much so their detection is disputed.

Water ice is by far and away the most likely ice here.

Jon

[Warren Platts]

However, I must admit I am confused by conflicting reports in the media. The SPACE.com article suggests that dry ice would sublime at the Phoenix site:

Phoenix's robotic arm first revealed the crumbs about 5 cm deep in the trench called "Dodo-Goldilocks" on June 15. By June 19, they had vanished. If the crumbs had been salt, they wouldn't have disappeared, scientists said, and if the ice had been made of carbon dioxide, they wouldn't have vaporized.

Yet the Bloomberg article I sited above says:

Salt wouldn't vaporize, and dry ice, or frozen carbon dioxide, exists at much cooler temperatures than found at the Phoenix landing site.

thus apparently implying that there shouldn't be CO₂ there at all.

[01101001]

However, I must admit I am confused by conflicting reports in the media. The SPACE.com article suggests that dry ice would sublime at the Phoenix site:

I agree that no weight should be given to the Space.com's reporter's mangling of the words of investigator Mark Lemmon. I listened to that briefing live. This Planetary Society Weblog account by Emily Lakdawalla jibes with what I heard:

Mark likened it to the stability of water ice on Earth at a temperature of 140 degrees Fahrenheit [...]. It won't vaporize instantly, but it won't stick around long. The biggest chunks in the trench survived at least one sol, but disappeared after two or three, which is exactly consistent with the predicted behavior of water ice, but not with carbon dioxide ice.

[John Jones]

Phoenix's robotic arm first revealed the crumbs about 5 cm deep in the trench called "Dodo-Goldilocks" on June 15. By June 19, they had vanished. If the crumbs had been salt, they wouldn't have disappeared, scientists said, and if the ice had been made of carbon dioxide, they wouldn't have vaporized.

I read the link to space.com, and it does indeed say that.

I can only presume it was an error that the editors missed, because everybody with a semester of college chemistry knows better than that.

[MaDeR]

As far I know, it cannot be dry ice.
"CO2 vs. H20 ice: Temp too high and pressure too low for CO2 ice. " (phoenix twitter)

And Warren seems to not know (or not understand question) about hydrogen detected by Mars Odyssey on poles - exactly where Phoenix is.
http://science.nasa.gov/headlines/y2...ay_marsice.htm

[aurora]

So you think there is significant quantities of methane or ammonia near the surface over the entire Martian polar region?

[Warren Platts]

Look, I'm not an expert, but I do know that conclusions that those light colored gravels must be water are overblown and premature.

[JonClarke]

Look, I'm not an expert, but I do know that conclusions that those light colored gravels must be water are overblown and premature.

If you are no expert, why must you take your opinion that these conclusions overblown and premature seriously?

Jon

[Warren Platts]

If you are no expert, why must you take your opinion that these conclusions overblown and premature seriously?

Methane is sold only at -185.2 degrees. That is way too cold for Mars. The only way that methane can be in the solid state at maartian temperatures is as a water-methane clathrate, which has six molecules of water to one of methane.

Ammonia is not solid about -77 degrees. Maybe clathrates are posssible, but these are going to be predominantly water ice again.

If there were abundant methane and ammonia clathrates about you would expect there to be traces of these compunds in the atmsophere. If present they are so in vanishingly small quantities, so much so their detection is disputed.

Water ice is by far and away the most likely ice here.

Jon

It's the philosopher of science in me: we send this probe with all these fancy instruments; so why announce that the ""Proof"" that there's water ice consists of a comparison of two photos? I say let's wait for what the oven says is the case first before we go forming solid opinions.

And your other point about ammonia and methane shows that everyone already supposedly knows that the proposition that water must exist is a forgone conclusion and therefore, any mystery crystals must be water ice, and so alternative hypotheses are ruled out before the game even begins.

[JonClarke]

It's the philosopher of science in me: we send this probe with all these fancy instruments; so why announce that the ""Proof"" that there's water ice consists of a comparison of two photos? I say let's wait for what the oven says is the case first before we go forming solid opinions.

If you were a philosopher you would know that science does not work that way. There is no "proof" only a succession of provisional hypotheses.

And your other point about ammonia and methane shows that everyone already supposedly knows that the proposition that water must exist is a forgone conclusion and therefore, any mystery crystals must be water ice, and so alternative hypotheses are ruled out before the game even begins.

Not at all. It is simply the contextural knowledge that allows us to interpret the evidence that we have. On the basis of what we know about frozen gases, the composition of Mars, and the ambient conditions water ice is the most likely explanation. It is, of course provisional, and you are welcome to come up with alternatives. But none of the alternatives you have mentioned - CO2, CH4, NH3 - match the evidence.

Jon

[jlhredshift]

But none of the alternatives you have mentioned - CO2, CH4, NH3 - match the evidence.

Jon

Would a second picture of the same trench at a later time to see if any sublimation occurred, constrain the possibilities?

[Warren Platts]

If you were a philosopher you would know that science does not work that way. There is no "proof" only a succession of provisional hypotheses.

That's what I'm sayin'. Yet "proof" is the word that the Phoenix scientists are using:

"It's with great pride and a lot of joy I announce today we have found proof that this hard material really is water ice and not some other substance," Phoenix principal investigator Peter Smith of the University of Arizona, Tucson said at a briefing Friday. (SPACE.com)

Not at all. It is simply the contextural knowledge that allows us to interpret the evidence that we have. On the basis of what we know about frozen gases, the composition of Mars, and the ambient conditions water ice is the most likely explanation. It is, of course provisional, and you are welcome to come up with alternatives. But none of the alternatives you have mentioned - CO2, CH4, NH3 - match the evidence.

I'll grant you the mystery chunks aren't CH₄ or NH₃, but I'm not convinced that it couldn't possibly be CO₂. Heck, they could be chunks of salt that were later covered over by dust.

True the case is not completely proven. But keep in mind it was the fact that the hydrogen readings suggest there is abundant water ice there in addition to the fact it sublimated as expected for water ice not CO2 ice that led to conclusion it was water ice.

It's the combination of both these facts that strengthens the argument.
There is another instrument on the robot arm called the TECP that can do measurements on the ground that might be able to give firmer evidence on whether or not there is water/ice there. They should be giving its readings over the next few days.

Actually, they didn't even bother to land Phoenix in the high water concentration regions. Check out this map. The Phoenix probe is at 68^o north latitude and 233^o east longitude. If I did the math right, that would correspond to a longitude of -127^o according to the system used on the map. Thus, the probe lies smack in the middle of the section bounded on the bottom by -120^o, that is, in the middle of the green lobe extending in the upper left of the picture. But green corresponds to relatively little water compared to the blue and violet zones around the pole. So, after everything is said and done, don't be surprised if they don't find any water where they're at.

If I was running the show, I would have sent the probe to the area of low relief in the violet zone that's at about 80^o north, and at 0^o longitude. There would be a better chance of actually finding water.

[RGClark]

It's the philosopher of science in me: we send this probe with all these fancy instruments; so why announce that the ""Proof"" that there's water ice consists of a comparison of two photos? I say let's wait for what the oven says is the case first before we go forming solid opinions.

And your other point about ammonia and methane shows that everyone already supposedly knows that the proposition that water must exist is a forgone conclusion and therefore, any mystery crystals must be water ice, and so alternative hypotheses are ruled out before the game even begins.

True the case is not completely proven. But keep in mind it was the fact that the hydrogen readings suggest there is abundant water ice there in addition to the fact it sublimated as expected for water ice not CO2 ice that led to conclusion it was water ice.
It's the combination of both these facts that strengthens the argument.
There is another instrument on the robot arm called the TECP that can do measurements on the ground that might be able to give firmer evidence on whether or not there is water/ice there. They should be giving its readings over the next few days.


Bob Clark

[Woodlock]

Is wet

<img src="">

[marsbug]

It looks like ice, it sublimates like ice is expected to and the orbiter data showing huge amounts of hydrogen in the top 5-10 cm of soil is consitent with H2O not CO2. Thats not cast iron proof but it is very suggestive of water ice.

[skrap1r0n]

ok I am going to ask a dumb question here, but if water ice sublimates, then wouldn't it be considered "Dry Ice" as well? What I mean is. Isn't dry ice is considered to be dry ice because it sublimates under normal earth atmospheric conditions, or is "Dry Ice" only solid CO^2?

[aurora]

Isn't dry ice is considered to be dry ice because it sublimates under normal earth atmospheric conditions, or is "Dry Ice" only solid CO^2?

Yes to the last. "Dry ice" is what speakers of American English commonly say instead of "Frozen Carbon Dioxide". I've never heard the phrase refer to any other solid.

[HypothesisTesting]

ok I am going to ask a dumb question here, but if water ice sublimates, then wouldn't it be considered "Dry Ice" as well? What I mean is. Isn't dry ice is considered to be dry ice because it sublimates under normal earth atmospheric conditions, or is "Dry Ice" only solid CO^2?

If water sublimed on earth, then it would also be considered a form of dry ice. On earth, only CO2 sublimes, so that's the only one they call dry ice.

But now on Mars, they have found water subliming (or maybe technically being liquid over an undetectable range of temps.) , because the Martian pressure is about at the triple point for water (6 millibars). So a case could be made to name water ice "dry ice" if you're referring to water on Mars.

[Squink]

On earth, only CO2 sublimes

Water ice sublimes quite nicely on earth.
One way to see the results of sublimation is to hang a wet shirt outside on a below-freezing day. Eventually the ice in the shirt will disappear.
A dusting of snow will disappear over the course of days, even with temps below 0°F; that's sublimation.

[John Jones]

Water ice sublimes quite nicely on earth.
One way to see the results of sublimation is to hang a wet shirt outside on a below-freezing day. Eventually the ice in the shirt will disappear.
A dusting of snow will disappear over the course of days, even with temps below 0°F; that's sublimation.

You beat me to it.

Yes, water has vapor pressure even below the freezing point, so it does sublimate on earth.

[HypothesisTesting]

Water ice sublimes quite nicely on earth.
One way to see the results of sublimation is to hang a wet shirt outside on a below-freezing day. Eventually the ice in the shirt will disappear.
A dusting of snow will disappear over the course of days, even with temps below 0°F; that's sublimation.

I agree . But technically scientists refer to "equilibrium" phase changes like melting, sublimation, etc., occuring at a phase change temperature at a certain atmospheric pressure. Like for water, it has to be below 6 millibars for the system to be in equilibrium sublimation; if non-equilibrium, any phase change is possible at any temperature , pressure like evaporation at room temp. and pressure, etc., but very slowly.

The really Alice in Wonderland point is the triple point where solid-liquid-vapor water can exist in equilibrium 0 celcius and 6 millibars.
http://en.wikipedia.org/wiki/Triple_point

[geonuc]

On earth, only CO2 sublimes, so that's the only one they call dry ice.

I've noticed the effects of sublimation in my freezer's ice tray many times.

[HypothesisTesting]

I've noticed the effects of sublimation in my freezer's ice tray many times.

I have seen that too, good point. (But technically, thermodynamic sublimation can only occur for a atmospheric pressure below 6 millibars for water. That is, the temperature has to change across the phase point for it to be technically sublimation. What is happening in freezer is a non-equilibrium situation where the molecules slowly ablate off the solid ice. )

[alainprice]

Correct, the martian ice is supposedly sublimating water ice.

[MaDeR]

If someone looked at newest raws - ice patches still darkens. Sublimate, girl!