3 ms·

It seems like, being under ground, it would also be subject a higher than normal pressure, which would also help

simias 8y ago
I was wondering about that, how deep is it exactly? If TFA mentions it I missed it. Given the planet's low gravity and very thin atmosphere I presume it must be pretty deep in order to remain liquid. They mention Lake Vostok at the end of the article which is 4km deep but it's probably not directly comparable.
- AnimalMuppet 8y ago
  It says 1.5 km down. I'd expect there to be significant pressure down there. Enough to make it liquid at -10C? I suspect so, but I'm not an expert on the pressure gradient on Mars...
  - gmueckl 8y ago
    Mars only has a surface gravity of about 3.71m/s^2 compared to Earth's 9.81m/s^2. This means that 1.5km of ice will just create something like 0.38 times the pressure the same column of ice of the same density would create here on Earth. If this ice were densely packed, the mass of a 1m^2 column of ice that high would be a bit less than 1400 tons. This creates a pressure of 5.1MPa or around 51 bar. Now if I could get my hand on a phase diagram for water on which I could find that point (263K, 5.1MPa) I could tell you how close pure ice is to melting under these conditions.
    - the8472 8y ago
      The melting point does not really budge much for standard water. https://upload.wikimedia.org/wikipedia/commons/0/08/Phase_diagram_of_water.svg https://upload.wikimedia.org/wikipedia/commons/0/08/Phase_di...
Tushon 8y ago
(not a scientist, but was skeptical of this statement given the general "incompressibility of water") From looking at the phase change chart[0], you don't really get into the "interesting" stuff as far as pressure goes until pretty deep (something like 9-10km, from looking at some sample number of pressure at various depths [1]). Given that they indicated in the article that this is under 1.5km of ice, I don't think that's deep enough to have pressure significantly change it, but would be happy to learn that I'm not correct in my reading of this :) 0 - https://physics.stackexchange.com/questions/60170/freezing-point-of-water-with-respect-to-pressure https://physics.stackexchange.com/questions/60170/freezing-p... 1 - https://www.earthlearningidea.com/PDF/189_Pressure_rock.pdf https://www.earthlearningidea.com/PDF/189_Pressure_rock.pdf - table on page 2
- forapurpose 8y ago
  A few considerations that may influence this question: Pressure != compression, and water is otherwise sensitive to pressure. The boiling point of water varies by ambient air pressure, and in fact, the ambient air pressure on the surface of Mars is too low for liquid water, AFAIK; it boils away. Also, see gmueckl's helpful comment: https://news.ycombinator.com/item?id=17610197 https://news.ycombinator.com/item?id=17610197

I was wondering about that, how deep is it exactly? If TFA mentions it I missed it. Given the planet's low gravity and very thin atmosphere I presume it must be pretty deep in order to remain liquid. They mention Lake Vostok at the end of the article which is 4km deep but it's probably not directly comparable.

AnimalMuppet 8y ago
It says 1.5 km down. I'd expect there to be significant pressure down there. Enough to make it liquid at -10C? I suspect so, but I'm not an expert on the pressure gradient on Mars...
- gmueckl 8y ago
  Mars only has a surface gravity of about 3.71m/s^2 compared to Earth's 9.81m/s^2. This means that 1.5km of ice will just create something like 0.38 times the pressure the same column of ice of the same density would create here on Earth. If this ice were densely packed, the mass of a 1m^2 column of ice that high would be a bit less than 1400 tons. This creates a pressure of 5.1MPa or around 51 bar. Now if I could get my hand on a phase diagram for water on which I could find that point (263K, 5.1MPa) I could tell you how close pure ice is to melting under these conditions.
  - the8472 8y ago
    The melting point does not really budge much for standard water. https://upload.wikimedia.org/wikipedia/commons/0/08/Phase_diagram_of_water.svg https://upload.wikimedia.org/wikipedia/commons/0/08/Phase_di...

Tushon 8y ago

(not a scientist, but was skeptical of this statement given the general "incompressibility of water") From looking at the phase change chart[0], you don't really get into the "interesting" stuff as far as pressure goes until pretty deep (something like 9-10km, from looking at some sample number of pressure at various depths [1]). Given that they indicated in the article that this is under 1.5km of ice, I don't think that's deep enough to have pressure significantly change it, but would be happy to learn that I'm not correct in my reading of this :) 0 - https://physics.stackexchange.com/questions/60170/freezing-point-of-water-with-respect-to-pressure https://physics.stackexchange.com/questions/60170/freezing-p... 1 - https://www.earthlearningidea.com/PDF/189_Pressure_rock.pdf https://www.earthlearningidea.com/PDF/189_Pressure_rock.pdf - table on page 2

forapurpose 8y ago
A few considerations that may influence this question: Pressure != compression, and water is otherwise sensitive to pressure. The boiling point of water varies by ambient air pressure, and in fact, the ambient air pressure on the surface of Mars is too low for liquid water, AFAIK; it boils away. Also, see gmueckl's helpful comment: https://news.ycombinator.com/item?id=17610197 https://news.ycombinator.com/item?id=17610197