"Earth radiates more heat than it gets from the sun."

[chorpler]

In this thread (http://boards.straightdope.com/sdmb/showthread.php?t=392591), I mention an argument about global warming, and Eurograff pointed out that climate on a gas giant is different from cliamate on Earth, because they generate internal heat that drives the climate.

Well, when I mentiond that in my argument, somebody responded "So does the Earth, due to radioactive heating. On both Earth and Jupiter, hurricanes are driven by a temperature difference. On both Earth and Jupiter, the temperature *difference* results directly from solar heating, plus indirectly by factors which are themselves driven by solar heating. I don't see any important difference there."

Apparently, he thinks that the situations on Earth and Jupiter are directly comparable, and both are caused by an increase in solar radiation. Does that make any sense at all?

[mks57]

I don't know if they are directly comparable on anything other than a gross level. Solar radiation is going to generate temperature differentials on the surface of both planets, providing the energy source for storms. How do you model heat flow for a gas giant? Are there large convection currents transporting heat to the surface?

[Freddy the Pig]

In this thread (http://boards.straightdope.com/sdmb/showthread.php?t=392591), I mention an argument about global warming, and Eurograff pointed out that climate on a gas giant is different from cliamate on Earth, because they generate internal heat that drives the climate.

Well, when I mentiond that in my argument, somebody responded "So does the Earth, due to radioactive heating."Jupiter radiates about twice as much energy as it receives from the Sun. With Earth, the difference is hardly measurable--I've seen estimates on the order of one part in 10,000. (In other words, Earth on average radiates 1.0001 times as much energy as it receives--a difference which would be swamped by any minor diurnal or seasonal warming or cooling.)

[chorpler]

Jupiter radiates about twice as much energy as it receives from the Sun. With Earth, the difference is hardly measurable--I've seen estimates on the order of one part in 10,000. (In other words, Earth on average radiates 1.0001 times as much energy as it receives--a difference which would be swamped by any minor diurnal or seasonal warming or cooling.)

Thanks Freddy. This is exactly the kind of quantified data I was looking for. One page on RealClimate said that 99.998% of Earth's energy output comes from insolation and 0.002% come from "geothermal sources," which is somewhat similar to your figure.

[Hari Seldon]

Jupiter radiates about twice as much energy as it receives from the Sun. With Earth, the difference is hardly measurable--I've seen estimates on the order of one part in 10,000. (In other words, Earth on average radiates 1.0001 times as much energy as it receives--a difference which would be swamped by any minor diurnal or seasonal warming or cooling.)

I don't know the actual figures, but what I do know is that Lord Kelvin, not knowing about radioactivity, estimated that the earth's age could not be more than 100 million years (and he estimated that it was actually more like 20 million) or it would have cooled much too far to support life. Perhaps the difference is slight, but in 100 million years it would add up.

As a matter of fact, the sun is slowly warming up and the difference, if any, is going to decrease, until we all fry in a couple billion years.

[Freddy the Pig]

I don't know the actual figures, but what I do know is that Lord Kelvin, not knowing about radioactivity, estimated that the earth's age could not be more than 100 million years (and he estimated that it was actually more like 20 million) or it would have cooled much too far to support life. Perhaps the difference is slight, but in 100 million years it would add up.No, I think all Kelvin was saying is that the interior of the Earth would have cooled off more than it had. Even a geologically dead Earth could still support life--the interior would be much cooler, and there wouldn't be any plate tectonics, but the impact on surface temperature would be negligible.

[chorpler]

No, I think all Kelvin was saying is that the interior of the Earth would have cooled off more than it had. Even a geologically dead Earth could still support life--the interior would be much cooler, and there wouldn't be any plate tectonics, but the impact on surface temperature would be negligible.

Would a cooled-off mantle and core, and the associated lack of plate tectonics and vulcanism and the like, eventually cause all of the land to be eroded away completely?

[Diceman]

So why does Jupiter radiate so much energy? Is there fusion going on inside of it?

[Freddy the Pig]

Would a cooled-off mantle and core, and the associated lack of plate tectonics and vulcanism and the like, eventually cause all of the land to be eroded away completely?Good question. Venus and Mars are less geologically active than Earth, and are far from flat, but then they don't have oceans. I don't know--any planetologists out there?
So why does Jupiter radiate so much energy? Is there fusion going on inside of it?No, the interior of Jupiter isn't hot enough for fusion. The heat source may be gravitational contraction, or it may be that Jupiter, unlike Earth, is still dissipating its original "heat of formation". (Or it may be a combination of the two.) I don't believe this has been resolved, unless there has been a recent breakthrough.

[Askance]

So why does Jupiter radiate so much energy? Is there fusion going on inside of it?No, but Jupiter would not have to be much bigger in order to be a star. From Wikipedia:Jupiter is thought to have about as large a diameter as a planet of its composition can; adding extra mass would result in further gravitational compression, in theory leading to stellar ignition ... the smallest red dwarf is only about 30% larger than Jupiter. In light of this, it is also interesting to note that it radiates more heat than it receives from the Sun. This additional heat radiation is produced by the Kelvin-Helmholtz* mechanism.* essentially that gravity is compressing the gas of the planet, generating heat, in the same way that compressing air in a bicycle pump makes it hot.

[Chronos]

That just says that Jupiter's radius is as large as it can get, but mass-wise, it would have a way to go before it started burning. You need to get up to about 13 times Jove's mass before you can even start burning deuterium (considerably easier than H1). I'm not sure off the top of my head what the threshhold is for H1, but it'd be somewhat higher yet.

[chorpler]

OK, somebody just said:

"Researchers already knew that Jupiter radiates into space almost twice as much heat as it absorbs from the sun." http://www.space.com/scienceastronomy/solarsystem/jupiter_weather_000209.html

So over half of Jupiter's heat comes from insolation-- from sunshine.

I've learned something in this discussion-- I've learned that Jupiter's internal heat provides a much greater percentage of its heat output than I previously thought. And hopefully you ... have learned that over half of Jupiter's heat comes from the sun, and therefore it is the *predominant* source of energy driving Jupiter's hurricanes.

and:

Hurricanes are driven by a temperature differential, which on Earth is primarily due to uneven heating between day and night. If Jupiter storms are driven by internal temperature, where is the differential coming from? I'd think the heat would leak out more or less evenly in all directions. Jupiter's oblate shape might cause heat to leak out faster near the poles, which *might* provide some temperature differential. I rather doubt it's as much as the
difference between night and day, tho. It's true Jupiter only receives a fraction of Earth's insolation, but the amount of internal heat generated by Jupiter isn't all that great, either.

Quoting from:
http://www.ajax.ehu.es/grupo/2006.pss.egm.pdf
~~~~~~~~~~~~~
The deduced high velocity at the 6 bar level is difficult to understand under
the hypothesis that solar insolation alone drives Jupiter^�s circulation. The
internal heat source may play a significant role.
~~~~~~~~~~~~~

It sounds like he's saying insolation is the primary engine of Jupiter's winds,
with internal heat probably a contributing factor. Sounds reasonable to me.

Does that make sense? Is he right to assert that most of Jupiter's climate energy comes from the sun rather than from internal sources? Something seems wrong there to me, but I can't tell what it is, or if I'm just insane.

[Der Trihs]

Good question. Venus and Mars are less geologically active than Earth, and are far from flat, but then they don't have oceans.Actually, Venus is active, but in spurts according to some theories. Instead of the constant earthquakes and volcanos we see here, every few hundred million years the whole planet resurfaces itself in a worldwide cataclysm.

As a matter of fact, the sun is slowly warming up and the difference, if any, is going to decrease, until we all fry in a couple billion years.A hundred million years is the last estimate I've heard; that's when the greenhouse effect will go into runaway mode and we become Venus II.