Celestia Forums

Hey people. I was just thinking, would it be possible for a planet to have enough atmospheric water to support huge tropical rainforests and swamps across most of its surface (not on mountains/ice caps) without there being any major oceans, seas, or lakes? Or if you had that much water in the atmosphere, would it just rain out to produce oceans and lakes? Im not limiting it just to Earth-type worlds, what effect would a thin/thick atmosphere have? Or a warmer world? ^_^

Thanks.

This belongs in the physics section, not Celestia development --- so I'm moving it.

Knowing absolutely nothing about everything, I would yes it is possible providing that the planet is warm enough that global temperature does not fluctuate that much between the equator and the pole. This would probably me that the atmosphere would have to be very think, probably two to three times the earth?€™s current thickness. Historically the earth as been warmer and wetter in the past, and I see to recall that most of the word was covered by a primordial rain forests.

Thanks Selden, soz

Yeah, I was thinking that, a heavy thick atmosphere. Also I was thinking it would have to have less tectonics, so that mountain ranges and ocean basins arent so extensive - that way the lower areas wouldnt be so deep, and would just become broad swamps between the drier rainforest areas, right?
Also a thicker atmosphere would hold water in suspension in the atmosphere better, so that rain wouldnt be quite so sudden...this would spread the rain out over a larger area, possibly letting it fall into seperate watersheds, so less rain falls in each area...

After thinking about it, I don?€™t think you can have all of the surface covered by forests, but you could have most of the planet covered by land with a few massive seas. Water will always seek the lowest area, and it doubtful that the land is so perfectly flat that the water would pool evenly. So what you are left with is a planet ~with 70% land with lots of big flowing rivers empting out in inland seas.

So basically, we're looking at a world that maintains a water cycle through the atmosphere exclusively, rather than oceans and seas being the primary motivator, yes? I want to get this straight before I jump in on the idea bandwagon....

...John...

That would be my guess

Alright. So right off, I would have to say that unassisted Huamn life would not be able to exist here. If you have an atmosphere that dense, and that filled with water, then it is also going to have a heck of a greenhouse effect. I would guess that the surface temperate would average in the triple digits, planetwide, year around. And the surface would probably be covered, not so much with a forest as it would be with a massive and tangled globe-spanning matt of intertwined vegetation. You might get a thickness of several hundred feet, and things would likely be thicker the higher one got. The very bottom of the "forest" floor would probably be relatively open, but the ground would be covered with a very thick layer of mulch. Great fodder for any animal life that might have evolved here, though....

It would probably look something close to this. Unfortunately I can make the atmosphere thicker in this system to compensate for higher temperatures. The planet should be greener

From what was described, I wouldn't expect to see any differentiation between land and ocean, aside from some seas and lakes where the topography is fairly low.

A generally flat topography would also probably be the result of no tectonics and plenty of aeolian erosion. So the question is: can you have a world like this, rich in water and oxygen and CO2, and NOT have some sort of geological cycle?

...John...

Dollan wrote:Alright. So right off, I would have to say that unassisted Huamn life would not be able to exist here. If you have an atmosphere that dense, and that filled with water, then it is also going to have a heck of a greenhouse effect. I would guess that the surface temperate would average in the triple digits, planetwide, year around. And the surface would probably be covered, not so much with a forest as it would be with a massive and tangled globe-spanning matt of intertwined vegetation. You might get a thickness of several hundred feet, and things would likely be thicker the higher one got. The very bottom of the "forest" floor would probably be relatively open, but the ground would be covered with a very thick layer of mulch. Great fodder for any animal life that might have evolved here, though....

Triple digits in what temperature scale? If it has Earth's insolation, plus enough CO2 to make plants grow profusely, plus enough water vapour to drive the water cycle, that's a lot of greenhouse. I think it might be over 100C. That's rather hot.

So the world would probably be farther from its sun than the Earth. If it's a swamp world, it would likely have lots of CO2 to make the plants grow well. With the water vapour, the world would have to orbit farther from its sun - maybe 50% farther - to be inhabitable by humans.

Dollan wrote:From what was described, I wouldn't expect to see any differentiation between land and ocean, aside from some seas and lakes where the topography is fairly low.

A generally flat topography would also probably be the result of no tectonics and plenty of aeolian erosion. So the question is: can you have a world like this, rich in water and oxygen and CO2, and NOT have some sort of geological cycle?

...John...

That?€™s my fault for not pointing that out more. The program doesn?€™t allow you to set the height. It has to be +- 30,000ft, which blows up the image in the fist place. But that said, still having only 30% covered by seas is still the equivalent of the entire Atlantic Ocean which is a lot of water.

Well down deep on the forest floors you could have standing water covered by what esentialy would be like a massive mangrove swamp. So in some ways it would be like the planet Dagobah in Star Wars The Empire Strikes Back. If you had any humans living here they would probably live high up in the canopy of such a forested planet. Far from the stagnate standing water of the surface. Most higher life forms would be up in trees. This is of course just my humble opinion though.

Don. Edwards

Cool, its making more sense now... a very thick, humid atmosphere, rain falling constantly onto a thick spongy canopy, huge leave supported by the thick air from the top of giant 1000ft-tall trees. Water pours down between them down through tangled vines and branches, with huge insects flitting about in the high O2 beneath them. The greenary fades as the light is blocked out by the thicker plant life overhead. The water collects and pours down over giant fungi growing from the tree trunks, small treetop animals feeding from them. Far down below the water falls into a dark hot swamp, millions of smaller insects buzzing around blind, surviving from the animals unlucky enough to fall from the trees above - of course, they would've died from the pressure increase long before they hit the water...

Anchored to the trunks of the giant trees, suspended above the thick black water, large pressurised bases support human colonists, trying to survive

I think M-Dwarf stars with a high IR ratio and probably tidally locked planet may host such a world. I created a similar system in my SciFi Comics

The planet must be in the inner part of the habitual zone as well.

Red1530 wrote:The planet must be in the inner part of the habitual zone as well.

Of course. For example:

AD Leonis - Flare star

Spectral type: M3.5Ve
Habitable zone = 0.11 - 0.13 AUs

A "Rainforest planet" could be located at 0.095 - 0.11 AUs.
In my opinion...

I'd guess that to stop it turning into a Venus, you'd want the planet to be quite far out.

I'm not sure about this, but I doubt you'd have enough light reaching the surface to support photosynthesis.

The scenario just doesn't seem likely to me.

What I was thinking about definatly wouldnt work around an M-type Dwarf. To be close enough to get the needed heat to keep most of the planets water vapourised in the air, it would become tidally locked, and obviously green (or other coloured) plants could never grow on the dark side, leaving a whole hemisphere with no plants

I was thinking more about a K or F type maybe... theyre both cooler than G types right?

from hot to cool:
O B A F G K M

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