How do "intermediate" hot terrestrial planets look like?

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How do "intermediate" hot terrestrial planets look like?

Post by Neuron on 23rd March 2012, 6:02 pm

We all know how Venus looks like (and Mercury, but we haven't found planets of such mass range yet) and we can infer that planets closer than cca 0.05 AU around a Sunlike star are going to be molten or even evaporating, but how do planets in the 0.6 to 0.05 AU distance from a Sunlike star like Kepler 20e or 20f look like? Of course, this range is very wide so there is going to be a big variation.

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Sirius_Alpha on 23rd March 2012, 6:37 pm

Neuron wrote:Of course, this range is very wide so there is going to be a big variation.

I think this is about the best kind of answer you could hope for.
I'll go out on a limb and say that if they are indeed terrestrial, like the planets in our solar system, then I expect them to have either minimal atmospheres or thick, insulating atmospheres with Venus-like environments. But my imagination is perhaps too strongly based on the Solar System.

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Neuron on 23rd March 2012, 6:54 pm

What about a medium sized atmosphere? Too much radiation for a Venuslike one, but not enough to create a Mercury? What about a volatile rich thick atmosphere? Transiting super Earths in that temperature range I mentioned have them.

Or a "clarified Venus"? Venuslike, but without clouds, having a thick and with a molten/semi-molted surface due to the greenhouse effect (1200 K is the upper limit)? Like John's (RIP) vision of 55 Cancri e (which was in meantime discovered to have a supercritical ocean of volatiles on its surface instead) http://extrasolar.net/planettour.asp?StarCatId=&PlanetId=268 , just smaller, and with the greenhouse effect really raising the temperature from 400-750 K to 1200 K instead of a starhug (less than 0.04 AU) orbit.

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Sirius_Alpha on 24th March 2012, 11:49 am

Transiting super Earths in that temperature range I mentioned have them.
But those transiting super-Earths are also a lot more Neptune-like than Earth-like, as far as bulk composition is concerned. I would expect them to have enormously thick atmospheres.

This paper might be of some interest to you. It discusses the stability of atmospheres for super-Earths in the range you mention.
http://solar-flux.forumandco.com/t1032-stability-of-super-earth-atmospheres-in-m-dwarf-habitable-zones

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Re: How do "intermediate" hot terrestrial planets look like?

Post by tommi59 on 24th March 2012, 3:49 pm

Most of the planets we discuss I guess are ocean planets
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Re: How do "intermediate" hot terrestrial planets look like?

Post by Neuron on 24th March 2012, 7:58 pm

I am not talking about "ocean planet" stuff. Exoplanets certainly aren't as simple as that. It might turn out to be wrong anyways (just like "Venus is a jungle" or "Mercury must be totally tidelocked"), rather, planets like Kepler 20e and f - Earth mass not quite on a torch orbit but almost. Those planets are basically certainly rocky and not "ocean mini-Neptunes", hell, Kepler 20e is And I am not talking about red dwarf "Super-Earths" either. Thanks for answers anyway through.

I am not talking about "Super-Earths" (a misleading term that leads people to think lavaballs 5x as massive as Earth are "Earthlike"). There have been multiple worlds below 4 Earth masses discovered and some even less massive than Earth, like for example Kepler 20e and f or those recently discovered hot Mars sized planets in a red dwarf system.

And supercritical fluids don't require a "mini-Neptune" at all. Venus's atmosphere is actually supercritical CO2. And indeed, standing on Venus would feel more like being in an ocean than in the air. It has a solid surface but yes, an atmosphere of supercritical CO2. Dense enough to create optical distortions similiar to that of water and certainly dense enough for a human (if he could survive) to fly using his own body/or more accurately should we say swim? Yet Venus is a clear terrestrial with a rocky surface and smaller than Earth. What I am proposing is not some gassy mini-Neptune, rather, a planet like Venus, but with water/steam as the supercritical atmosphere. Those are not "ocean planets", they have a normal surface and the supercritical fluid acts as an atmosphere, not as a liquid. Many people seem to think supercritical fluids are just "very hot liquid water", this impression is absolutely wrong. A supercritical steam atmosphere is not more of an ocean than Venuses's supercritical CO2 one is. It is basically just gas so dense it has some liquid-like properties. Supercritical fluid on a planet's surface is not an ocean, but an atmosphere. Supercritical fluids have no surface tension, you cannot have a pool of supercritical CO2/water on a planet's surface. Venus's atmosphere is supercritical carbon dioxide, well, the lower levels are. It smoothly transitions into "true gas" CO2 with altitude. Supercritical water on terrestrial planet's surface would just be a Venus density steam atmosphere. Just like the one Earth had just after it was born.

Water loss by UV could be an issue, but systems with hot Jupiters are tought to have very water rich terrestrials. Not necessarily "superterrestrial" - after all, most rock+ice bodies are small.

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Sirius_Alpha on 24th March 2012, 8:24 pm

"Venus is a jungle"
There was never any evidence for this nor was there ever a good reason to believe this to be true. The jungle idea was just a hope and fuel for science fiction. No one was surprised that it didn't turn out. I'll give you the Mercury one, bearing in mind that it was not known about spin-orbit resonances at the time, and why Mercury fell into a spin-orbit resonance other than 1:1 has been a ongoing problem in physics until relatively recently.

Bear in mind that the transiting super-Earths discovered to date require a substantial amount of light materials to explain both their mass and radius (and therefore density).



And I am not talking about red dwarf "Super-Earths" either. Thanks for answers anyway through.
The paper I mentioned goes onto discuss K and G type stars as well.

I am not really sure what you are trying to get at. You go from talking about super-Earths to not talking about super-Earths, and going from talking about Venus-like atmospheres to not talking about Venus-like atmospheres. What exactly is the topic?

Neuron wrote:Water loss by UV could be an issue, but systems with hot Jupiters are tought to have very water rich terrestrials. Not necessarily "superterrestrial" - after all, most rock+ice bodies are small.
For the specific examples of Kepler-20 e and f which you mentioned earlier, and according to the discovery paper, UV-driven water loss would cause the e-planet to lose its water within a few hundred Myr. The f planet could retain water if it has a thick vapour atmosphere of 0.05 ME, and thus a Venus-like, insulating atmosphere, which seems to be what we've both mentioned so far.


Last edited by Sirius_Alpha on 24th March 2012, 8:29 pm; edited 1 time in total (Reason for editing : Added link to the discovery paper.)

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Neuron on 24th March 2012, 8:37 pm

I just mentioned super-Earths as an example of volatile rich planets.
And yes, I am talking about thick Venus-type atmospheres, but not Neptunes. Horribly dense, but thin enough to have a normal surface. The "surface" of Neptune is a layer of weird water as hot as Earth's outer core.
And I am talking about all at once because there are many possiblities. No, nobody really tought Venus is a jungle but nobody really predicted it to be a runaway greenhouse.

Could the Kepler 20 e retain CO2? Can you give a link to the paper please?

Sorry if I am a bit rude, I am just tired of those "Super-Earths" and "ocean planet" cliches. A supercritical fluid is the kind of steam that powers turbines, not just super hot liquid water. And most "Super-Earths" are very far from Earthlike.

Could there be an "evaporated Neptunes" class of planets? Like those "hot ocean planets" that lost almost all water, except for a thin supercrtical steam layer as the atmosphere, just the catch being that "thin" still means like Venus. After all, Venus's atmosphere is a near vacuum compared to the pressure at the atmospheric depth where Neptune's water mantle starts.

To clarify the mass range I am interested in, it is 4 Earth masses to cca 0.8 Earth masses. Not massive enough to be a hot Neptune or mini-Neptune, not small enough to be totally airless.

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Sirius_Alpha on 24th March 2012, 8:47 pm

Could the Kepler 20 e retain CO2? Can you give a link to the paper please?
Not sure. Here's the paper. http://arxiv.org/abs/1112.4550v1

I am just tired of those "Super-Earths" and "ocean planet" cliches. A supercritical fluid is the kind of steam that powers turbines, not just super hot liquid water. And most "Super-Earths" are very far from Earthlike.
You're amongst people who know what those terms mean though. We all know super-Earths aren't habitable, just like we know "hot Jupiters" aren't expected to have Great Red Spots and Galilean Satellite analogues. Earth, being the most massive planet in our solar system, is a sort of prototypical terrestrial planet, just like Jupiter is a prototypical gas giant planet. As you're surely aware, everything that makes our planet habitable is confined to a very thin envelope on its surface. So one might reasonably say that Venus and Earth are very similar in bulk composition, and thus that Venus is an Earth-like planet, which is to say that it is a small, rocky, silicate-dominated planet. It doesn't seem reasonable to characterise an entire planet based on that upper thin film on its surface.

Could there be an "evaporated Neptunes" class of planets?
Most likely. I would imagine it would be very similar to how evaporated Jupiters form. Some planets, like Kepler-10 b and CoRoT-7 b are candidates for having been much more massive planets in the past. It seems reasonable that a Neptune could migrate in and lose its H-He envelope, and be just left with a water envelope.

To clarify the mass range I am interested in, it is 4 Earth masses to cca 0.8 Earth masses. Not massive enough to be a hot Neptune or mini-Neptune, not small enough to be totally airless.
The atmospheric escape would of course be a function of both the planetary mass and the planet's insolation from the star. Push Titan into an Earth-like orbit and the atmosphere will get up and leave. Push Earth into a tight, 3-day orbit and I'm sure ours would do the same.


Last edited by Sirius_Alpha on 24th March 2012, 9:03 pm; edited 1 time in total (Reason for editing : Clarification "we all know super-Earths aren't Earthlike" vs "we all know super-Earths aren't habitable.")

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Neuron on 25th March 2012, 5:29 am

Sirius_Alpha wrote:The atmospheric escape would of course be a function of both the planetary mass and the planet's insolation from the star. Push Titan into an Earth-like orbit and the atmosphere will get up and leave. Push Earth into a tight, 3-day orbit and I'm sure ours would do the same.

Sure, we are not talking about 3 day orbits through. That is why I wrote intermediate planets. I mean, basically, the "grey area" between our Venus and torch orbit exoplanets. An Earth-sized planet orbiting for example 0.5 AU, from its Sunlike star is certainly not going to lose it's atmosphere. It is also almost certainly hotter than Venus.

How could a "clarified Venus" look like? Venus has sulfuric acid clouds, but if it was closer to the Sun those clouds would evaporate. Would clouds of another condensate form or would it be just clear atmosphere + some dusty clouds?


Last edited by Neuron on 25th March 2012, 5:56 am; edited 2 times in total

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Neuron on 25th March 2012, 5:51 am

Also, can a steam/supercritical water atmosphere be clear and bluish from Rayleigh scattering? Usual artwork depicts hot planets with a watery atmosphere as white steamy, but that is because steam released into enviroment which is below the boiling point of water and condenses into water droplets. At those temperatures, water droplets would not form. Could Kepler 22f look like John's vision of 55 Cancri e http://extrasolar.net/planettour.asp?StarCatID=normal&PlanetID=268 , with a molten surface by greenhouse effect and a thick but clear atmosphere of steam/supercritical water?

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Sirius_Alpha on 25th March 2012, 10:08 am

I can't think of a reason why a steam/supercritical water atmosphere wouldn't have Rayleigh scattering. I think it's a function of the scattering particle size. That being said, I don't really know much about that topic so I would be unsurprised if I've overlooked something.

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Neuron on 25th March 2012, 11:46 am

It is clear that Rayleigh scattering could apply, but wouldn't an extremely dense atmosphere without clouds be red? We can see this effect when Sun rises or sets - during sunrise or sunset it looks like it would normally look from the surface of a planet with an atmospheric pressure of 30 bars.

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Sirius_Alpha on 25th March 2012, 12:09 pm

It's a function of the viewing angle, too. The blue light is scattered more or less isotropically, and the red light continues on. If you were to be "behind" this "clarified Venus" you might observe it to have a reddish crescent like Earth.

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Neuron on 3rd April 2012, 2:02 pm

Could Kepler 20f have clouds of sulfides and chlorides? Sudarsky scale predicts it http://en.wikipedia.org/wiki/Sudarsky_extrasolar_planet_classification#Class_III:_Cloudless , although it is only for gas giants, I guess terrestrial planets could have a cloud composition like a gas planet that is in the same temperature range (Earth has water clouds and Sudarsky scale predicts water clouds for gas giants with Earthlike temperatures).

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Lazarus on 3rd April 2012, 2:49 pm

Sudarsky scale is not gospel. The actual observations of hot Jupiters show there is a wide variety in the properties, and the ones for which we have best data for appear to have reflection properties similar to Neptune.

Applying the Sudarsky system to terrestrial planets does not work: the chemistry of these planets is very different. The gas giants have hydrogen-rich chemistry, while the chemistry on terrestrial planets is oxygen-rich and hydrogen-poor.

(By "oxygen-rich" I am referring to compounds that contain oxygen, not just the free oxygen we have in our atmosphere.)
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Re: How do "intermediate" hot terrestrial planets look like?

Post by Neuron on 3rd April 2012, 4:28 pm

True, but cloud condensates are not that much influenced by the fact if it is a hydrogen atmosphere or oxygen-rich. Can atmospheric chlorides and sulfates exist on hot terrestrials?

And other hot Jupiter were proven to have extremely low albedos. Black in fact (well still blinding white considering the insolation at those distances from the star but you see my point... albedos at cca 1 percent).

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Re: How do "intermediate" hot terrestrial planets look like?

Post by Lazarus on 4th April 2012, 3:18 am

Well the overall atmospheric chemistry will influence what's in the atmosphere. And the differing molecular weight of the atmosphere and greenhouse properties are going to result in different temperature/pressure profiles and suchlike.

E.g. Whatmough extrapolated a "sulphur-cloud Jovian" class from Venus. However the sulphuric acid clouds on Venus are a result of a chain of chemical reactions from volcanic sulphur dioxide (and H2SO4 is an oxygen-rich molecule), whereas on a gas giant the sulphur tends to be in the form of hydrogen-rich molecules like H2S, NH4SH, (NH4)2S etc. Whatmough's extrapolation is therefore probably wrong.
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Re: How do "intermediate" hot terrestrial planets look like?

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