Earth Underground Temperature: Hot or Cold?

[W3pcq]

I was just thinking about how the temperature on Earth at a certain depth is always a certain temp even when it is cold or hot out. On a planet, or moon like say Titan or venus, what would be the temperature say 20' or so underground? Also, if extreme temperatures on the surface won't permit liquid water, couldn't there still be liquid water underground?

 

[jim mcnamara]

When I had a soils courses eons ago, the idea about temperature was this: the temperature near the surface (say less than 10') will change with the seasons. As you go down it begins to approximate the yearly average temperature above ground.

The average surface temperature of Venus is 461C. So at 20' down, if there are soils present, then that's the temperature there. Much hotter than your kitchen oven.

Ditto Titan. Except the Huygens probe seems to show that "soils" there are made of water ice and methane ice, and possibly clathrates. So the temoperature must be below the freezing point of methane - which has to be well below -161.1C the boiling point of methane. About -180C or -292F is what I can find quickly.

 

[DrClapeyron]

Depends on the mineralogy of the depth at question and its pressure. Perhaps there is a geothermometer that could answer your question, may be the best way to go. As for the water question, I suppose that is why the nerds at NASA are still sending probes to mars. Here on earth, at least, there are places where water does not exist (but for vapor) on or above the surface but certainly below, like a desert.