# Thermal output of earth

1. Apr 13, 2010

### dirtyd33

Is the thermal output, or rather electromagnetic output, of the earth's core relatively constant? and if so, how does it compare to the output of other interstellar cores, say like mercury or the sun?

2. Apr 13, 2010

### Matterwave

Which one are you asking? Thermal output or electromagnetic (i.e. radiative) output?

For cores, this is very different. The thermal energy of the core would be dissipated by conduction and convection as well as radiation...The radiative aspect of this transport is actually not efficient since the Earth is opaque.

3. Apr 15, 2010

### dirtyd33

My answer to you is yes. I meant the total thermal output of the earth, from the core outward. I want to know if it is fairly constant/ continuous and what might it's capacity be. But now I think of it I'd like to know just the radiative aspect separately, as well.

4. Apr 16, 2010

### sylas

The total rate of thermal energy coming up from below the Earth's surface is about 44 TeraWatts.

This is a heat flow mainly by conduction and convection; radiation has essentially no role below the surface.

This energy flux has only a negligible contribution to the much larger heat fluxes above the surface, which are dominated by radiation from the Sun.

The geothermal heat flux from the core works out to be a bit under 0.09 W/m2, which is negligible by comparison with the energy absorbed from the Sun, which works out to be a bit over 160 W/m2.

The energy absorbed at the surface then flows up through the atmosphere and eventually out into space. The outward energy flows are about 17 W/m2 by convection, 80 W/m2 by latent heat of evaporation, and about 63 W/m2 by radiation (radiation here being the difference between thermal radiation upwards and thermal backradiation from the atmosphere). The geothermal flux is several orders of magnitude less than the energy flows above the surface.

Cheers -- sylas