What would be the hottest possible Cytherean (= Venuslike) world?Could it go even so hot to have a molten surface without the temperature and stellar winds becoming too strong to mantain it's hyper thick atmosphere?And could there be a class of natural terrestrial planets that have even thicker atmospheres and hotter enviroments than Cytherean planets (I mean both extremely thick atmosphere and hot temperature, not just hot or high pressure alone) ?

All terrestrial planets (as well as our Moon) had molten surfaces at one time.

So both Venus and Earth were molten and maintained an atmosphere.

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I don't know, no offense, but sometimes any of you seem to me to take everything only-as-it-is-written, like if you were sufferers of Asperger's syndrome or computers.

Thank you, but I tought it was clear from my post that I was writing about hot planets well after the solar system formation hot phase, with characterics similiar to that of present day Venus, with extremely thick atmospheres and extremely high temperatures due to a runaway greenhouse effect of the superthick, almost entire made of greenhouse gases, atmosphere.

And to specify I mean atmosphere stable in geological time scales, not like in the case you specified when the planets had solid surfaces after a few thousands years as there was nothing to maintain that extreme heat on the surface.

And afaik in the molten surface stage of evolution of terrestrial planets the primordeal atmospheres were made of primarily primordeal hydrogen and helium from the accretion, and were less dense than even our atmosphere of Earth today, and that only after the surface was solid and temperatures were lower than even these on today's Mercury and Venus (they were in the 100-200 degree Celsius range) a thick "second" atmosphere made of mostly water vapor, CO2 and acidic gases developed from the gases released by extensive young terrestrial planet's volcanic activity, that was around 100x thicker as ours nowadays on Earth (it had pressure around like now on Venus) that quickly rained out to oceans and become around Earth pressure on all three terrestrial worlds except for Mercury where it was quickly blown off from it's weak gravitational field combined with high temperature even without any greenhouse effect and solar wind (however it along with oceans survived from all three worlds only on Earth because sadly the Venus and Mars were unable to maintain the necessary condtions to this time, Mars fell to freezing and thin relic atmosphere and Venus is a hot hellhouse planet now).

It appears that Venus slagged down completely 500-750 million years ago! Does that count?

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Sorry, are you all really so ignorant?
I said hot and with dense atmospheres SUSTAINED OVER GEOLOGICAL TIMESCALES .
If you don't know what to answer, please rather do not answer than to tell something that is irrevelant to discussion.

Okay, m1omg, since you are being so sweet and pleasant I'll put in my two cents.

Your talking about heating the atmosphere until the heavier gases can overcome the one gee of gravity and escape. That would take more than a molten surface to do. You would just make the atmosphere puff out more.

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Sorry, I apologise, I did not mean any offense, I was just annoyed because I specified my answer 2 times and you still did not understand my question properly and it did not happened for the first time.

Well, but the termosphere temperature is aready around 2000 degress even here.
That's the temperature that matters, not the surface temperature.
And lets not say 1 G, but the gravity of the largest probable natural superterrestrial, say, 15 Earth masses.
According to this applet; http://www.transhuman.talktalk.net/iw/Geosync.htm
the temperature to which 15 Me planet can retain CO2 atmosphere is 37533 degress Celsius, compared to Earth's maximum of 5942 degress Celsius.

However, there is a problem and that is; that I don't know how to calculate thermosphere temperatures (which are dramatically higher than surface) and I don't know how to take the effects of solar wind into account.

Is there any expert on this who would be able to help me, please?

Make the planet closer to the sun, and larger; this will allow the atmsphere to remain dense despite being much hotter. A Venus-like (Cytherean) world with about 1.5 gees at Mercury's distance could be very hot on the surface; bigger planets would be even worse. Ultimately the atmosphere will have silicon vapour clouds as well as, or instead of sulphuric acid clouds. The night side would probably glow, as well. But perhaps we should make up a new name for such hellish worlds.

One planet which might resemble a superVenus in some ways is Gliese 876d;
http://en.wikipedia.org/wiki/Gliese_876_d
it has a mass of around 7.5 Earths, and is almost certainly molten on the surface thanks to tidal heating if not because of any potential greenhouse effect.

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Thanks! And also, could the atmosphere be even denser and more turbolent than that of Venus?If so, by what process it can become so thick?

And what is the limit to how close to the planet could be to the sun with retaining it's entire superdense atmosphere assuming a limit of terrestrial planets mass of 15 Earth masses?

BTW, what is the hottest Cytherean world in your OA project?And how thick is the atmosphere of the hypothetical cthonian planet Sysiphos in OA?Are Cthonian planets (these after the gas giant atmosphere has been blown off) theoretised to have even thicker and "greenhousier" atmospheres than Cytherean?

About Gliese 876, well, I think the conditions there must be extremely hellish.Tidal heating 10000-100000x stronger than on Io, maybe high pressure water-CO2 greenhouse atmosphere....That planet must be hotter than some red dwarf stars on the surface, I would guess!

Btw there would be a very big region of distances and temperatures, from around 80 to 900 degress Celsius in the upper atmosphere (Venus has much lower temperatures in the cloud layer) where no condensate could be and so these world will be cloudless, the question is; would the surface be seen as blurred because even without clouds the 90-100 bar atmosphere scatters the light or would be the surface not seen at all because the atmosphere will scatter the light to that point when the sky would be pure white and so the planet will be seen from space as white, with a thick blue border because of the Rayleigh scattering?

Could we expect to see superVenus type planets without clouds? I know some hot gas giants should be too hot for water vapour clouds so would be essentially cloudless- these are the so-called clarified Jovians
see this page for more info
http://www.extrasolar.net/speculations.html
Clarified Jovians fall into the range 350-900 Kelvin; Venus has a temperature of 730K at the surface but it has clouds of sulphuric acid droplets at higher altitudes where it is cooler. I'd expect most superVenus type planets to have high altitude clouds of some sort.

But if a superVenus is hot enough to be clarified completely, you should be able to see the sky from the surface- I'd expect it to be creamy white, if the atmosphere was above 40 bars.

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Once again, I think we are into uncharted territory. What is left when a gas giant has lost its H and He? Nitrogen and argon perhaps- neither are very good greenhouse gases.

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But won't be the new (not the gas giants former) atmosphere form from the volcanism of the naked core, producing CO2, SO2... I mean standart volcanic gases, if we assume that the core is composed of what an ordinary terrestrial planet is?Are are gas giant cores supposed to have much different composition?Enlighten me please, I was under the assumption that the core is basically a super terrestrial planet after the former atmosphere gets blown off, and that because of its mass it will have great volcanic activity that will release a lot of greenhouse gases including CO2 and water vapor, or no ?

Will the volcanic activity release just a lot of nitrogen and argon due to the remaining core not containing CO2, water etc.?I would guess that more CO2 than N2 will remain in the core, due to N2 being less dense than CO2 and so N2 being more able to escape from the planet in the evaporation phase of the gas giant.
Argon is more dense than CO2, but I think much less abundant, if our Earth had no limestone, carbonates, dissolved CO2 in the waters etc...its atmosphere would have about the same amount of CO2 as Venus and Earth has retained all its noble gases in the atmosphere expect for helium since its birth but still, only 1 percent of our atmosphere is argon so if there was no carbon cycle there would be about 10 000x more CO2 than Ar.

How much gas could a Cthonian planet contain to release through volcanism?

Possibly. I've just checked Hebrard et al, which just says 'hydrogen poor or even with no more atmosphere at all'.
http://fr.arxiv.org/PS_cache/astro-p...12/0312384.pdf
So we don't have much to go on.

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Thanks!

However CO2, SO2... are much heavier gases than hydrogen.
Even our own planet cannot retain H2 gas, even He gas escaped.


So does it remain a mystery?

Thanks.

So they will be visible as engulfed in white "clouds" from the space?
And will the whiteness increase with pressure?If so, should be hot Venuses/SuperVenuses seen as brilliantly white from space?
And if you standed on the surface of such planets, will be everything engulfed in white "haze" or only the sky will be white?What would be the visibility on such a planet if the pressure is 90 bars of CO2?

BTW that was exactly the page that I was reading.

The above was just 1 significant figure estimate. Now I did an actual calculation assuming star's mass 32 times Jupiter, semi-major axis exactly 3 million km, and eccentricity 0.22. To two sig fig, tidal buldge will vary from 930 meters at perihelion to 250 meters at aphelion -- 680 meters difference, so 46 times energy per kg as Io. I was off by almost an order of magnitude. Still, this is far cry from "10000-100000 times", and smaller eccentricity would result in much smaller het output.

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http://en.wikipedia.org/wiki/Gliese_...Orbit_and_mass

"Due to its extremely eccentric orbit, models predict that tidal heating will play a significant role in the planet's geology. In fact, they predict that the planet may well be kept in a completely molten state. Predicted total heat flux is approximately 10(exponent)4-5 W/m2 at the planet's surface; for comparison the surface heat flux for Io is around 3 W/m2.[4]

[edit] "

???Which one is right?

References http://arxiv.org/abs/0803.0026 .