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Exothermic Planet's atmosphere's thermal gradient

Jimbo schlomp

New Member
So I am planning a world where the planet produces a lot of heat, and the sun produces relatively little heat, and mostly just light. I am thinking that if the air on the ground is significantly warmer than the air above it, people could create a device that flies by "floating" on the hot air. I am not sure if the air could possibly have a difference in temperature great enough though. I feel like since it is an entire planet, then the atmosphere would kind of normalize.

Also, some considerations are that the planet is roughly the size of our moon, so its atmosphere is relatively thin. I think this would increase the thermal difference, making my idea more possible. as well, because of its small size, it has a gravity between 1/2 and 3/4 of the earth. (it is very dense)

One thought I have as I write this is that if the whole planet is always hot, then air couldn't really circulate properly. Perhaps if just part of the planet is warm, then this idea would work better.

Thanks in advance for any help.
 

Eduardo Ficaria

Troubadour
I don't know if you've already done it, but I'd recommend you research the planets and moons on our solar system to get a better grasp of how such a planet could be. For a hot planet read about Venus, which is under a rampant greenhouse effect and it also seems to have notable volcanic activity, and also is smaller than our Earth. For something even smaller you could check Io, one of the many Jupiter's moons, that has the most active volcanic action in the whole solar system.
Said that, unless you're planning to use some sort of magical or technological trickery to explain the particularities of your world, small astronomical objects like moons or asteroids usually don't really have an atmosphere worth the name. Essentially, they neither have the gravity nor the magnetic field to hold and protect such gaseous envelope around them. For reference, check Mars and its thin atmosphere. Also, be aware that hot air is harder to breathe in since the molecules density drops due to expansion: molecules get further apart from each other the hotter they get. You should also take that into account for the beings living in that world of yours. And not forget about gravity either, in the Moon is quite low so if you're not careful your flying device could very well take you to orbit the planet or beyond!
 

Jimbo schlomp

New Member
I don't know if you've already done it, but I'd recommend you research the planets and moons on our solar system to get a better grasp of how such a planet could be. For a hot planet read about Venus, which is under a rampant greenhouse effect and it also seems to have notable volcanic activity, and also is smaller than our Earth. For something even smaller you could chelo ck Io, one of the many Jupiter's moons, that has the most active volcanic action in the whole solar system.
Said that, unless you're planning to use some sort of magical or technological trickery to explain the particularities of your world, small astronomical objects like moons or asteroids usually don't really have an atmosphere worth the name. Essentially, they neither have the gravity nor the magnetic field to hold and protect such gaseous envelope around them. For reference, check Mars and its thin atmosphere. Also, be aware that hot air is harder to breathe in since the molecules density drops due to expansion: molecules get further apart from each other the hotter they get. You should also take that into account for the beings living in that world of yours. And not forget about gravity either, in the Moon is quite low so if you're not careful your flying device could very well take you to orbit the planet or beyond!

Hey, thanks so much for your reply. I am a pretty scientific person, and my goal is to make this as near to what could actually be possible as possible. As in, I want it to be realistic. I am willing to have some amount of magic "holding" the world together so to speak, but I am not sure what my magic system will be yet, so I don't want to rely too much on that.

Venus is actually kind of the opposite of what I was looking for, as it is hot due to proximity to the sun and the greenhouse effect. In my world, I want the sun's energy to actually be quite small, and for the planet itself to produce a large amount of heat. I will definitely look into lo. I am aware that the smaller a planet, the less atmosphere it usually has. Something I forgot to mention is that the density of the planet is very high, leading to gravity of 1/2 - 3/4 that of the earth, while being smaller than the moon. For reference, the moon has a gravity about 1/6th that of earth. I believe a high density planet is likely to be much hotter than a lower density planet, due to the increase in pressure causing greater frictional forces within the planet. as well, I think a higher density planet likely means that the collision that caused the formation of the planet was very high energy, and therefore, made the planet very hot initially.

I do think your point about the atmosphere is a concern. Mars lacks atmosphere mostly due to a lack of magnetic field causing the atmosphere to be stripped away by solar flares. I'm not sure exactly what type of star the planet will orbit, and how much of a concern solar flares are. However, with the high density of the planet, I'm hoping that there would be enough of an atmosphere.

That's fair about the hot air being harder to breathe but I'm not sure it will be an issue, as surface temperatures will be similar to hot places on earth (30-40c). as well, I am considering making some alterations to the atmosphere, such as having a higher amount of oxygen. Not really sure of this yet though.

So I think based on what you have said, I will do some more research into star types, magnetic fields, and try to approximate an atmosphere thickness. I think based on that, I could probably compare the temperature of earth's atmosphere are various heights, and then try to get a rough estimate of the force of the convection currents caused by the warm planet.

Thanks so much for your reply!
 
I'm not sure it makes that much of a difference where the heat comes from. I think most of the heat absorption happens when the sun strikes a solid surface. Especially the warmer infrared rays pass through most of the atmosphere without too much interference. Which means that it's the ground doing a lot of the heating, which is not all that different from when the planet is doing the heating. Also, note that even the earth has a fair bit of internal heating (mainly coming from radioactive elements and pressure).

A main difference will be that climate zones are different. Earth climate zones exist because the sun heats the bits at the end less than those in the middle. If that effect is smaller because most heat is internal, then you will have smaller differences between equator and poles in terms of climate.

Be careful with using Io as a model. The reason it has such a high level of volcanic activity is mainly because of its proximity to Jupiter, which keeps ripping up the surface and moving the magma inside it. It's less to do with an internal process. For an internal source of heat, you're mainly looking at radioactive isotopes inside the planet.

As for stars, you can go with a small star. Some dwarf stars give of relatively little heat. They'll probably also have fewer sun-flares (though that's just an asusmption on my end), which might fix your atmosphere issue. Just be aware that the light is also likely to be more towards the blue end, which might impact vegitation (plants are green because we get a lot of green light, something like that).
 

Jimbo schlomp

New Member
I'm not sure it makes that much of a difference where the heat comes from. I think most of the heat absorption happens when the sun strikes a solid surface. Especially the warmer infrared rays pass through most of the atmosphere without too much interference. Which means that it's the ground doing a lot of the heating, which is not all that different from when the planet is doing the heating. Also, note that even the earth has a fair bit of internal heating (mainly coming from radioactive elements and pressure).

A main difference will be that climate zones are different. Earth climate zones exist because the sun heats the bits at the end less than those in the middle. If that effect is smaller because most heat is internal, then you will have smaller differences between equator and poles in terms of climate.

Be careful with using Io as a model. The reason it has such a high level of volcanic activity is mainly because of its proximity to Jupiter, which keeps ripping up the surface and moving the magma inside it. It's less to do with an internal process. For an internal source of heat, you're mainly looking at radioactive isotopes inside the planet.

As for stars, you can go with a small star. Some dwarf stars give of relatively little heat. They'll probably also have fewer sun-flares (though that's just an asusmption on my end), which might fix your atmosphere issue. Just be aware that the light is also likely to be more towards the blue end, which might impact vegitation (plants are green because we get a lot of green light, something like that).


That's an excellent point I wasn't considering - how the sun mostly heats the earth, which then heats the atmosphere, rather than the sun warming the atmosphere directly. I was thinking about your climate point earlier. I think that the climate of the poles will essentially show how much of the heat comes from the sun vs the planet. it also depends though on how the planet rotates, which I haven't cemented in yet.

I wasn't really planning on using lo as a model, I was just going to look at it a bit. I don't think it's similar to my planet though. I don't think I am going to have many volcanoes, but haven't really thought too much about it yet. I have looked a little bit at what causes internal heat in a planet and it seems to be a mixture of radioactivity and the internal friction caused by stuff moving around in there. My planet should have a relatively high internal pressure due to the large density, so therefore it should have a high amount of internal friction, and therefore would be warm. I don't really know how accurate this line of thinking is, but I think it is good enough. Maybe the planet will also have a higher concentration of radioactive elements though, not sure.

I haven't really planned out my vegetation yet, but I know the star will affect it a lot. You are actually slightly wrong though, plants are green because plants don't absorb green light very much in comparison to red and blue light. I'll have to think about how the star type would affect plant colour and shape more. I am essentially going to look for the star type that would give off the least amount of solar flares, so my small planet can breathe properly. I would also assume a dwarf star would fit well, but Ill research it first.

Thanks for your reply!
 
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