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.

Comments

I still think it's CO2

[ookabooka]

...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."

Yeah, except one thing that wasn't addressed was the pressure of the dirt on top of the so-called "water". As we all know from elementary chemistry, increased pressure raises the temperature that CO2 can remain solid. Once the dirt was removed, the pressure was reduced (temperature remaining in the same range as before) and the CO2 started to sublimmate.
Furthermore, there is essentially no water vapor in the atmosphere on Mars, so how would water have gotten there in the first place? Atmospheric CO2 can condense when conditions are right. Atmospheric water can't condense if it doesn't exist.

There's some bait, lets see if anyone will bite :-D

Re:Standards....

[AlpineR]

Oh pshaw. The advantage of Imperial units over Metric is that the size of the units is a better match for our everyday experiences.

A foot is about the length of my foot. A pound is a filling dinner. And a pint is a refreshing amount of beverage.

-70 F is like room temperature but cold and -109 F is like too damn hot but too damn cold instead. In America, we don't have to use Google to figure out whether to wear a jacket to work.

Re:Standards....

[elrous0]

Fahrenheit is better than Celsius for delineating temperature. Celsius may be more standardized, but putting only 100 degrees between freezing cold and boiling hot makes for a pretty shitty scale for humans (unless you want to get into decimal points).