Subterranean Lifestores

I was recently thinking about ground source and geothermal energy. There was an alternative energy article that showed some of the "green" alternatives.

The ground stays at a constant temperature, once you go down a few feet. This means that caves and ground water around here are usually at a constant 56°F. You may have noticed this when letting the water run in your house for a long time, the cold water gets even colder after a while. This is because you are drawing your water from the a piping system that goes underground outside of your house. The pipes are supposed to be buried deep enough to avoid freezing. There are charts that tell you how deep to bury pipes in various parts of the country, and that depth is shallower in the south and deeper in the north. Below a certain depth, the ground stays at a constant temperature. I've noticed that the cold water seems even colder in the winter, after letting it run a while. I'm guessing that the pipes are buried in a zone that does get colder than 56°F as the outside temperature drops below freezing, but these pipes are not in the zone where they reach 32°F.

Some people heat and cool their houses using this trick of constant ground temperature. Heat pumps and air conditioners that are installed in your house normally get their heat or dump the house's heat to the outside air. In the summer, this means you are pushing your house's heat to a 95° or 100°F heat "sink". They say that "heat flows downhill", but what it does is flows from a higher temperature to a lower temperature. They call something a heat sink, the same way you would call a big depression in the ground a sink, which is where water would flow - downhill. It's easier to make heat flow to a 56°F heat sink of the constant ground temperature rather than the 95° or 100°F outside air. The AC only has to chill the air down 15° or 20°, rather than around 60°, which means it takes much less energy and cost to cool your house. In the winter, using a heat pump, you extract heat from the outside air. Even though it doesn't seem possible, a heat pump can find heat in the air on a cold day and push it inside. The limit to this is somewhere around 40°F, when the heat pump can no longer perform this magic trick any more. If you can use the ground temperature, you have a year round 56°F to draw heat from. If you have a heat pump in an area that goes below 40°F, you have to also have electric or gas heat to take care of you when it gets really cold. The heat pump is more efficient than electric or gas heat, and uses less energy.

The man that replaced my condenser on my air conditioner a few years ago told me that he cut his heating and cooling bills down to less than 1/3 of what they had been when he installed a ground source heat exchanger on his house. I've wanted to do this ever since.

I was thinking about how Earth has this constant underground temperature, independent of how hot or cold the climate or temperature for that particular day is. The earth (soil, sand, clay and rock) must be a great insulator, like a blanket on the planet. I know that the center of the earth is molten and very hot, but the layer near the surface is pretty cool and uniform.

I wonder if there is a constant ground temperature on Mars? How deep is it? If that temperature is above freezing (after all, Mars' core is not thought to be molten anymore, so this ground temperature could be very cold, or it might be like ours).
If it is above freezing, I wonder if there is life in that layer?

We should test for life in the thermally stable layer here on earth to see how well it survives being away from sunlight and air. I know they've found bacteria growth in special areas underground, but my question is whether there is still a variety of life in the constant temperature region. If there is, it is likely life is below the surface on Mars, too. That's assuming it was ever established there in the first place, but it's an interesting question that I hope NASA or JPL are working on.

This begs the question "What keeps the underground life alive?" I've heard reports of bacteria that use chemical reactions to get their energy and of ones that live near hot spots like volcanic vents or natural nuclear reactors (they exist - they are slow and steady). There have been methane blooms on Mars lately, which could have come from some kind of bacteria colonies that live under the surface. The question is what balances the subsurface temperature on Mars? Is there still some heat in the center of the planet, sufficient to keep a layer in the liquid water range? We believe there isn't a molten core, as evidenced by the lack of a magnetic field, but that may not mean the ground temperature is much lower. Maybe if we more there, we'll set up camp underground.