Cloud City - a possibility?

[peacekeeper]

I just read about this very interesting planet orbiting HD28185 (I hate numerial names like that btw). Apparently it's a water giant orbiting it's star - which is very much like Sol - at exactly 1 AU. That means that the upper layers probably consist of a vast beautiful cloadscape, not unlike what may sometimes be found here on earth (though much vaster of course).<br /><br />The planet is 5.6 times as heavy as Jupiter. Now, what would the gravity be like in the upper layers of that cloudscape? Would it be possible to build a "floating" (orbital) city within those clouds, at an altitude where the gravity would be 1g? Or would that specific altitude be far outside the planet's atmosphere?<br /><br />Since I am no expert on gravity, I might as well ask the following as well, just in case. How would the fact that the city is orbiting the planet affect the perceived gravity inside the city? I would think that it wouldn't matter, that those who lives in the city would indeed feel the force of exactly 1g, even though the city itself is "escaping gravity" with the high speed by which it orbits the planet. Would this be a correct assumption?

 

[peacekeeper]

Okay, I have now rephrased the question a bit, as well as added another one. The post should now be clear enough for anyone to understand it, and hopefully this will lead to a few answers starting to appear in this thread <img src="/images/icons/wink.gif" />

 

[thalion]

Ditto for Eburacum. However, it would not be impossible to get something to float in a hydrogen atmosphere--just use hot hydrogen, which would be that much more effective if the atmosphere were very cold, like Jupiter's. <br /><br />A gas giant Jupiter's age, but 5 times more massive would be roughly the same size as Jupiter, because of compression of its interior. Jupiter's gravity is already 2.4 times stronger than Earth's at its equator; on HD 28185 it would be five times stronger still, which translates to some 12 times Earth gravity. I'm pretty sure that would be intolerable for humans for anything but a very short interval of time.<br /><br />Unfortunately, on a planet Jupiter's size the 1 g level would be very high--well above the atmosphere at that--and the city would have be more or less motionless relative to the surface, just like a balloon would be in its atmosphere. In that case, it would fall like a stone, just like the ISS would fall if it were suddenly brought to a dead halt. It just wouldn't work, unfortunately. If the city were actually orbiting the planet, however, then everyone on board would still be in weightless; they would not feel 1 g of weight even if the gravity at their level were 1/12 that on the surface.<br /><br />That doesn't mean cloud cities are impossible, but we just need to find gas giants that don't have gravity much stronger than Earth's.

 

[peacekeeper]

Thank you for answering.<br /><br />The classification of this planet is supposedly a "water giant", which is something very different from a brown dwarf. I do not believe such a planet to be very dense at all. If it's the high mass that scares you, I can tell you that other, similair planets with smaller masses do exist. For example, Gliese 876 has a water giant of only 0.56 Jupiter masses orbiting within the habitable zone of the star. If such a planet were to have the same diameter as Jupiter, the upper layers of its atmosphere would only have a gravity of about 1.4g, right? And if the diameter of the planet would be as large as 1.5 times that of Jupiter, the gravity of the upper layers would conveniently creep down to less than 1g.<br /><br />And yeah, when I said "floating city", I didn't mean the city would actually be floating like a ship in water, but rather orbit the planet at an altitude low enough for its inhabitants to experience a gravity of 1g. <br /><br />Edit: I just read Thalion's post above. If the people of the city would be weightless due to the city orbiting the planet, then that idea would be quite useless indeed. That means I have to figure out some other way to make the city stay in the sky, without actually obiting the planet. Any suggestions?

 

[peacekeeper]

The city would of course be shielded from all such radiation.<br /><br />Regarding what you said about that "the closest they'd get to it (gravity control) would be a close-in orbit", what did you mean by that? I though that any orbit fast enough to even out the gravity and hence make the city "fly" would also make the inhabitants weightless. Isn't that the case?

 

[najab]

><i>Currently, there's no way of keeping even a very heavy plane off the surface of the earth for any real length of time. </i><p>Even on Earth we have airships capable of lifting over 150 tons which can stay aloft for weeks at a time. In a denser atmosphere around a gas giant, it would be possible to build much larger and more capable lighter-than-"air" vessels.<p>><i>Given the toxicity of Jovian planets' atmospheres from methan[e], ammonia, sulfur and other interesting things...</i><p>Do we know that <b>all</b> gaseous planets have toxic atmospheres?</p></p></p>

 

[najab]

><i>Yes. The composition is going to contain methane, ammonia and other substances.</i><p>But in what quantities?<p>><i>Ammonia is toxic...</i><p>To humans, yes.<p><i>...and it's quite, quite common in comets, jovian planets and the moons.</i><p>True, in this solar system. Is that <b>necessarily</b> so for <b>all</b> planetary nebulae?<hr />Argh, brain freeze. Not "planetary nebulae", I meant "protoplanetary disks". In other words, just because ammonia was common in the early stages of the formation of our solar system - and hence is common in the gas giants and comets - doesn't mean it <b>has</b> to be common in every solar system.</p></p></p></p></p>

 

[peacekeeper]

>>Is that <b>necessarily</b> so for <b>all</b> planetary nebulae?<br /><br />I for one do not believe that to be the case at all. Just because something like that is true in this solar system, doesn't make it so in every other system. A water giant, for example, would most probably not contain nearly as much methane or ammonia as the Jovians of Sol. In fact, they could be missing those gases altogeather!

 

[bobvanx]

A "water giant" could go through an atmospheric evolution, just as the Earth did, if it happens to have life evolve on it. Such a low-density world would probably have a smaller magnetosphere than Jupiter (less energy in the system), so it doens't seem unreasonable to guess that life could develop there. So even if NH3 is a common chemical in proto-planetary discs (which seems quite likely), the ammonia/methane/sulfuric acid/water atmosphere could evolve through life's respiration into a nitrogen/methane/water or nitrogen/oxygen/sulfuric acid/water atmosphere.<br /><br />Such a place, if the biota was dense enough, could appear to be colored by life's pigments: chlorophylls and anthocyanins, for example. Nutrients could upwell from deep in the planet's bowels, so you'd end up with a sort of atmospheric plankton.<br /><br />PS to Steve: I hope you can see I'm just hypothesizing here. I'm not making any value-based statements about whether such a world exists.

 

[najab]

><i>Ammonia is NOT just toxic to humans. It's toxic to most life as we know it. It's a rather good disinfecting agent.<br /><br />That you don't know it, well, the case rests. </i><p>Uhm, steve, you ever heard of nitrifying bacteria? There could be whole ecosystems based on the oxidation of ammonia.</p>

 

[tap_sa]

<font color="yellow">"Certainly no multicellular advanced forms of life can tolerate it, either."</font><br /><br />Plants love NH3, farmers around the world inject soil with it. It's the cheapest nitrogen fertilizer there is. The catch is that NH3 reacts with moisture in the soil and forms NH4+ which plants use directly or after being turned into NO3- by bacteria

 

[najab]

><i>I am not concerned with a few bacteria. Almost all life as we know it, esp. those plants, animals as well as pathogens bacteria, viruses, fungi) most likely to cause disease in humans, are destroyed by ammonia.</i><p>You should be concerned about those 'few bacteria'. If not for their action ammonia would be <b>much</b> more abundant (it's produced by the decay of organic material) and all the plants, animals, etc. would be in trouble.<p>><i>The odds are exceedingly high that NH3 is toxic to life on earth as we know it.</i><p>Yes, it is. But you're missing the point. Ammonia is toxic to life on Earth precisely because it isn't abundant. On another world, where it is more abundant, entire ecosystems could be established around the oxidation of ammonia. There's nothing fundamental about ammonia which means it will be toxic to <b>all</b> life.</p></p></p>

 

[najab]

><i>This is a non issue, totally irrelevant to the discussion.</i><p>I agree. Your digression into the toxicity of ammonia has nothing to do with the possiblity of floating a city in the atmosphere of a gas giant. One would assume that a race advanced enough to build such a structure would know how to deal with a little ammonia.</p>

 

[nexium]

Saturn has a cloud top gravity the same as Earth according to a very old source. This likely is due to Saturn being mostly hydrogen in it's interior and likely it's cloud tops. So cloud city can be supported with balloons filled with warm hydrogen. The gravity will be comfortable, hydrogen is not toxic to humans, but mixed with oxygen is very explosive, so we will have keep hydrogen below about 2%? in the habitat. Green plants however can likely do well in a hydrogen atmosphere with about 1% carbon dioxide and about the same amount of water vapor and oxygen. Fertelizer for the plants can likely be made from the Saturn atmosphere, but the process will likely be very energy intensive as trace elements that plants need are likely in parts per billion in the upper atmosphere of Saturn. It may be nessesary to import potassium for agriculture. The waste heat from the grow lamps could help keep the lifting hydrogen warm. 1% of the food and oxygen from plants is likely easy, but more will be challanging as suggested in the thread about biospheres. Ammonia apparently combines with other elements quickly as I don't think it has ever been used as poison gas in warfare, so it is likely less toxic than sulpher dioxide or chlorine. Neil

 

[arobie]

Peacekeeper,<br /><br />Hello.<br /><br />In orbit it feels like zero-gravity, but there is a way to 'create' a feel of gravity. If you've ever ridden a gravitron at an amusement park, or swung a bucket full of water (or anything) over your head, you know the concept. <br /><br />When you spin or swing something around, things in it are pushed outward. EX: A spinning gravitron pushes people outward against the wall and a swung bucket doesn't allow the water to fall out.<br /><br />If you take a space station, such as a circular ring space station, and spin it at the right speed, the people in it will be pushed outward toward the wall at 1-gee. If you are familiar with Halo the x-box game, the man-made halo in space does this. It spins to create gravity.<br /><br />If you wanted to creat gravity while in orbit, this is a way to do it.

 

[peacekeeper]

Yes, I am familiar with the concept, of course. But regardless of that, I must say your post inspired me greatly! I shall create a ringworld around a water giant! In order to get a realy nice view, the radius of the ring should be small enough for the ring to be within the atmosphere of the planet. Of course, if the ring is at an altitude where the gravity is 1g, that would mean it has to spin fast enough to create 2g in the other direction, in order for its inhabitants to feel just one g. Right? Of course, a ringworld would be much cooler if it was on its own, but that has already been made countless of times (Larry Niven's "Ringworld" and Bungee's "Halo" to name a few), and I guess we should try to stay at least a bit original in here <img src="/images/icons/wink.gif" />

 

[najab]

><i>IFF the concentration of NH3 is low enough the compound in soil is converted to a nitrate as it interacts with the acids in the soil.</i><p>Actually, it's more likely that the nitrifying bacteria will break it down, since acid strong enough to react with ammonia would probably kill the plant anyway, but you don't want to know about them, do you?</p>

 

[tap_sa]

<font color="yellow">"Those of us who know some botany know the outcome of your damaging experiment in NH3 on plants."</font><br /><br />Those of us who grow crops for a living know <b>how to apply NH3 to plants.</b><br /><br />Never said anything about sraying ammonia <i>on</i> the plants, specifically said about injecting it <i>into the soil.</i><br /><br />Here some general facts. Like you correctly stated free ammonia is very toxic.<br /><br />Here an example of commercial implements to use straight NH3 as a fertilizer. Check out that John Deere pulling injectors followed by a wagon labeled 'Anhydrous Ammonia'. That farmer is <i>not</i> trying to sterilize his field <img src="/images/icons/wink.gif" /> <br /><br />Ammonium nitrate is a good fertilizer too but it's more expensive because is more complex to manufacture. Soak AN with diesel oil, add a fuse and you have a devastating mean to express political dissatisfaction...