Space/Science — HabitableZone

Space/Science » in reply to What else can I call it?

It depends whether it is IMPORTANT or not
nick hoffman — (archived)

A greenhouse effect can "trap" or "multiply" an energy source by a small fraction. For instance, the Earth's surface is about 10% warmer than it would be without the atmospheric greenhouse (290 K vs 265 K).

Solar energy is at a scale of ~500-1000 watts per square metre. Radiogenic geothermal heat from a rocky planet like earth is of the order of 50 milliwatts per square metre, so it is an energy source at least 10,000 times smaller.

If we discount the fact that rock is actually a better insulator than air (atmospheres convect, [crustal] rock only conducts), a finger-in-the-wind calculation says that the combination of Earth's atmospheric greenhouse effect and geothermal heat is worth 2.5 THOUSANDTHS of 1K.

So, in the absence of solar radiation (or extreme tidal flexing) you would need an atmospheric greenhouse one thousand* times more powerful than Earth's to attain 2.5K above the cosmic microwave background temperature.

You would need an atmosphere 100,000* times more powerful to reach the melting point of water, at the surface

* You can substitute increased geothermal heat, but since this scales with radius, you're talking about a rocky planet with a mass of 1 billion earth's to get enough geothermal heat flow.

This sort of scenario works for Gas Giants. It does NOT in any circumstance work for solo rocky planets.

Log in or register to post.

The whole thread (39 posts)