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m1omg
2010-Oct-30, 06:52 PM
How hot a planet can get from greenhouse effect? This little calculator http://www.astro.indiana.edu/~gsimonel/temperature1.html tells me that from 0.4 AU a planet with the same atmosphere and albedo as Venus would start melting (it gives the temperature as 708 degrees Celsius, which is the temperature of "colder" lava) and by 0.16 it would practically be a molten lavaball, but would that occur?

Now supposing that the planet was massive enough (like the hot superterrestrials that are being discovered right now) to retain an atmosphere (unlike Mercury), would it get a Venus-like atmosphere because of outgassing from rocks + volcanism (just like what Earth would have had too if it hadn't had liquid water and stable carbonate rocks), or would different chemicals come into play?

I know that really hot terrestrials (like COROT-7b) are probably just balls of molten rock as hot as L-M class stars with only a trace atmosphere, but how would planets look in the 0.7-0.04 AU regime? I know I've asked this question 2 years ago, but I still don't know a clear answer and I am interested in this, because most of the lowest mass planets discovered recently are close to their stars (if they were not they wouldn't get detected by current technology) and I am curious about how they might look like, along with other possible planetary configurations.

Edit - On a second thought, this might be better suited in the Astronomy section, not Q&A. I welcome "non mainstream" speculations and guesses too (through not of the conspiracy/paranoia kind, I've seen stuff like that even about these planets ... once I found a website that suggest COROT-7b is inhabited and UFOs from it are visiting Earth ... sigh).

m1omg
2010-Nov-01, 10:36 AM
Sorry, but 65 views and no answers?

Hornblower
2010-Nov-01, 11:25 AM
Sorry, but 65 views and no answers?

Perhaps that is a tacit "We don't know."

m1omg
2010-Nov-22, 02:20 PM
Please. Nobody has anything to say about this?

John Jaksich
2010-Nov-22, 02:23 PM
I am reading through it---and may be I(?) can provide some comment?

John Jaksich
2010-Nov-22, 02:28 PM
My first response (?)----possibly there is some limit to which a "hot exo-planet" of which you speak would even exist --in the first place

Am I safe in guessing that this computational algorithm was used in a sort of Bode-type law approximation of ordering planets in a given exo-planet solar system?

John Jaksich
2010-Nov-22, 02:33 PM
The link is very informative ---I personally find it useful for a course I presently am taking in: The solar system---I believe that I will let my instructor in on your find---


Thanks alot

Cheers----

John

m1omg
2010-Nov-23, 08:50 PM
Sorry, thanks for responding, but I am a bit confused by your response :o

What Bode law algorithm are you speaking about? Titus-Bode law, as far as I know, is just a nice mathematical coincidence in our solar system. There are planets on many wild orbits, a very big part of them extremely hot, as planets closer to the star are detected more easily, including terrestrial, super-terrestrial and potentional watery worlds such as GJ 1214 b http://en.wikipedia.org/wiki/GJ_1214_b Mu Arae c http://en.wikipedia.org/wiki/Mu_Arae_c , 55 Cancri e (this one is white hot, but very massive too) http://en.wikipedia.org/wiki/55_Cancri_e etc.

The link that I provided in my OP is just an applet that calculates planetary temperature, however I ask, is there any "saturation point" of greenhouse atmospheres? Because if not, and this calculator is right, epistellar terrestrials with a thick atmosphere would be hot like an M class star.

Trakar
2010-Nov-24, 12:08 AM
Sorry, thanks for responding, but I am a bit confused by your response :o

What Bode law algorithm are you speaking about? Titus-Bode law, as far as I know, is just a nice mathematical coincidence in our solar system. There are planets on many wild orbits, a very big part of them extremely hot, as planets closer to the star are detected more easily, including terrestrial, super-terrestrial and potentional watery worlds such as GJ 1214 b http://en.wikipedia.org/wiki/GJ_1214_b Mu Arae c http://en.wikipedia.org/wiki/Mu_Arae_c , 55 Cancri e (this one is white hot, but very massive too) http://en.wikipedia.org/wiki/55_Cancri_e etc.

The link that I provided in my OP is just an applet that calculates planetary temperature, however I ask, is there any "saturation point" of greenhouse atmospheres? Because if not, and this calculator is right, epistellar terrestrials with a thick atmosphere would be hot like an M class star.

While there is always a maximum or peak contribution level given the general conditions of the senario, you seem to be asking about factors related to the basic physics of the greenhouse effect independent of specific senario situations. You would reach a natural upper limit as the atmospheric greenhouse gas molecules dissociated and/or absorbed enough energy to escape the planet's gravity well. Other than this, there is nothing that I can think of, which would prevent extreme temps. inherent in the basic radiation transfer physics of greenhouse gases.

m1omg
2010-Nov-24, 06:41 PM
I found something;

http://www.bautforum.com/showthread.php/85200-worldbuilding-Greenhouse-effect-calculation?p=1443327#post1443327


Mark Bullock did extensive modelling of Venus's atmosphere for his PhD thesis - which is available online - and he found that above about 925 K the emitted frequencies of the surface become too high for the opacity of a CO2 atmosphere to keep it in. Venus, thus, has a 'thermostat' which prevents it from getting warmer even with 1000 bars of CO2 available.

So, there seems to be a limit to greenhouse effect. However, what this limit would be with more insolation than Venus? Would the emitted frequencies cause the CO2 atmosphere to have basically no effect in very hot planets (more than 925 K hot even without any greenhouse effect), or would it increase the temperature, albeit only to a certain degree?

Trakar
2010-Nov-25, 04:38 AM
I found something;

http://www.bautforum.com/showthread.php/85200-worldbuilding-Greenhouse-effect-calculation?p=1443327#post1443327



So, there seems to be a limit to greenhouse effect. However, what this limit would be with more insolation than Venus? Would the emitted frequencies cause the CO2 atmosphere to have basically no effect in very hot planets (more than 925 K hot even without any greenhouse effect), or would it increase the temperature, albeit only to a certain degree?

This doesn't sound like its discussing a limit to the Greenhouse Effect, merely to its potential under the conditions represented by Venus,...unless you have a more direct reference indicating otherwise.

m1omg
2010-Nov-25, 03:32 PM
It is considering the properties of CO2 heat absorption, if I have understood it correctly then it should be valid for any planet with a dense CO2 atmosphere. Something at 925 Kelvins radiates at certain wavelenghts regardless of whatever it is on Venus or elsewhere, and CO2 can retain only certain range of infrared radiation, meaning that at 925 K the wavelenghts radiated from he surface are not going to be reatained anymore, and radiate back to space.

Trakar
2010-Nov-25, 10:34 PM
It is considering the properties of CO2 heat absorption, if I have understood it correctly then it should be valid for any planet with a dense CO2 atmosphere. Something at 925 Kelvins radiates at certain wavelenghts regardless of whatever it is on Venus or elsewhere, and CO2 can retain only certain range of infrared radiation, meaning that at 925 K the wavelenghts radiated from he surface are not going to be reatained anymore, and radiate back to space.

Bullock's papers seem to be talking about an effect of the particular composition, density and impinging radiations on Venus, though he does do some possible projections of various other specific exoplanet type situations, assuming he is correct and unless I am reading his papers incorrectly
http://www.boulder.swri.edu/~bullock/


If you are aware of a specific reference or direct, independent of circumstance, limits, I would be interested in examining it.

eburacum45
2010-Nov-25, 11:26 PM
This paper has an interesting graph (figure 1, the lower graph)
http://www.springerlink.com/content/1442151wv3pr0870/fulltext.pdf
This figure. (adapted from Kaltenegger and Selsis, or so it says), shows the CO2 level required to maintain an Earth-like temperature at increasing distance from a Sun-like star. When the pressure gets too high, the CO2 starts to condense, so the greenhouse effect won't work past a certain distance (not if you want an Earth-like temperature anyway).

The rest of that paper is very interesting, too.

John Xenir
2010-Nov-26, 12:46 AM
Here is some article I found some time ago, which speaks about Venus having such high surface temperature because of pressure, contribution of greenhouse gases is low http://wattsupwiththat.com/2010/05/06/hyperventilating-on-venus/

m1omg
2010-Nov-26, 09:20 AM
Here is some article I found some time ago, which speaks about Venus having such high surface temperature because of pressure, contribution of greenhouse gases is low http://wattsupwiththat.com/2010/05/06/hyperventilating-on-venus/

Sorry, but this is just stupid. If pressure somehow magically increased temperature, then the bottom of the Mariana Trench would be hot. Hint: it is a few degrees above zero there. Pressure is independant of the temperature. You know, logarithmic doubling of CO2 greenhouse capabilities only works up to cca 0.2 bars of partial pressure. This "days are dark on Venus" is irrelevant, because the IR radiation comes through, it does not depend on visible radiation, greenhouse effect works because of IR radiation being absorbed. But of course, some people will make up anything stupid to deny global warming.

Traces of water vapour are irrelevant when there are 90 bars of CO2 around. And Venus is supposed to have had a steam atmosphere until its evaporated oceans dissipated into space, with surface temperatures around 1500 Kelvin, melting the planet http://www.ncbi.nlm.nih.gov/pubmed/11538226
And the ad hominem attacks on Sagan because he smoked pot are making me incandescent with anger. He was a great sciencist, definitely better than whatever hillbilly wrote this article.

Yes, the upper layers of the atmosphere are cold. You know, most of the atmosphere, and greenhouse gases are below these layers. Without any atmosphere, Earth would be freezing cold, because of the absence of greenhouse gases. Mercury is hot even through the pressure on the surface is almost zero. The same about the Moon during noon atc.

EDIT - looking through the blog http://wattsupwiththat.com/ it is seems that it is obsessed with global warming denial.

The scientific consensus is that Venus's temperature is so high because of a runaway greenhouse effect. Somebody who thinks pressure magically heats up things regardless of energy from the Sun or inner heat (such as deep in gas/ice giants or inside of the Earth) fails physics forever.

By the way, no offense at you. I am just angry at the author of the article for peddling bad science to prove a political agenda.

Strange
2010-Nov-26, 10:26 AM
Here is some article I found some time ago, which speaks about Venus having such high surface temperature because of pressure, contribution of greenhouse gases is low http://wattsupwiththat.com/2010/05/06/hyperventilating-on-venus/

Ah yes, it is so reassuring when a "serious" article starts off with two paragraphs of ad hominem attack.

m1omg
2010-Nov-26, 11:07 AM
Ah yes, it is so reassuring when a "serious" article starts off with two paragraphs of ad hominem attack.

Exactly. And I forgot to mention also that the thermosphere, a very diffuse layer of the atmosphere, has a temperature of 2000 Kelvins (through you wouldn't feel it as it basically a vacuum). So much for the "high pressure = high temperature, low pressure = low temperature" excuse. And I am not even mentioning things like that the surface of the Sun is almost a vacuum yet it glows and is at 5850 Kelvins, that extremely diffuse gas between the galaxies is hundreds of millions of degrees hot etc...

John Xenir
2010-Nov-28, 03:07 AM
But is not that denser air traps heat more effectively?

Although I do believe that haze of of clouds has big contribution to current status of its atmosphere. As on Earth it's warmer when the clouds cover the sky, because preventing solar energy to escape back in space (most of it). Hazy planets (Venus and Titan) seem interesting to study. So I think there would not be such extreme conditions if the sky would be clear and surface seen from space. Or I am wrong?

neilzero
2010-Nov-28, 03:34 AM
My guess is: Pressure does indirectly contribute to the surface of Venus being hot, as it means a thicker atmosphere that can trap more heat and a longer escape path for the infrared photons. Likely Venus is well into diminishing returns, so it will be only a bit hotter as the Sun get hotter. If Venus heats to 3000 degrees k, the carbon dioxide will disassociate into oxygen ions and soot, which likely are less effective at retaining heat than carbon dioxide, so that is a limit. Likely there are other limits. Neil

m1omg
2010-Nov-28, 12:25 PM
Some gases trap heat more. This is why they are called greenhouse gases.

It is not the clouds or haze. Clouds actually reflect heat. If Venus was cloudless it would be red hot. And Titan is actually being cooled by the haze.

baric
2010-Nov-29, 07:03 AM
Here is some article I found some time ago, which speaks about Venus having such high surface temperature because of pressure, contribution of greenhouse gases is low http://wattsupwiththat.com/2010/05/06/hyperventilating-on-venus/

Wow, that looks like a terrible article.

"It's not the CO2, it's the high pressure"

/facepalm

baric
2010-Nov-29, 07:06 AM
My guess is: Pressure does indirectly contribute to the surface of Venus being hot, as it means a thicker atmosphere that can trap more heat and a longer escape path for the infrared photons.

Very indirectly. The pressure on Venus is such a big deal because it is a greenhouse gas that is supplying that pressure. More pressure = More CO2 = More warming.

If Venus was 92 bars of pressure and 99% Nitrogen instead of CO2, it would be a much, much cooler planet.

John Xenir
2010-Dec-14, 09:56 AM
Is there a list of greenhouse coefficient for most common elements and compounds (not the most efficient), including nitrogen, oxygen, hydrogen, .... ?

Trakar
2010-Dec-14, 03:45 PM
Is there a list of greenhouse coefficient for most common elements and compounds (not the most efficient), including nitrogen, oxygen, hydrogen, .... ?

http://en.wikipedia.org/wiki/IPCC_list_of_greenhouse_gases