A permanent storm?

[Ihe]

All good ideas. @Venusian Broon, I've been reading up some more, and the tidal-lock seems like a good choice (great link, btw) if I don't want a 95% water surface. I would have to figure out planet revolutions and rotation speed around the not-so-hot central star. It would need to be hot enough to evaporate liquids though, with rotation fast enough to move air currents and create permanent jet streams (is that even possible in tidal-locked planets?). A problem would be that constant sun exposure on one side would also create a runaway greenhouse effect IMO. And if the dark side solidifies its atmosphere, there would be no exchange of air masses between lit and dark sides. I'd have to engineer temperature fluctuations very carefully.

As for the hot-spot mountains in the sea-world, @psychotick, that would be another nice way of going about it. The mountains would have to be massive enough to have ~40-50% of its mass above the storm though (and made of very good heat-conducting material to transmit it down to sea-level), to keep absorbing sunlight and supply hot air down below (otherwise, once the storm covered the mountain, the heat would be absorbed and the storm would die down). This way, humans could live above the storm, on the massive peaks, with a storm carpeting the horizon below. Those would have to be truly massive mountains though (to rise out of the sea and then have about half its height above the clouds...). I don't even know if that sort of topography/rock formation is even possible on account of gravity, rotation, and eroding atmosphere, specially at the scale I want: we're talking of A LOT of mountains of about 30 km high each (or more, as I would need deep oceans). Olympus Mons is 25km, granted, but it's just the one, on a dry surface, in a place without many eroding factors. I'll have to research this option.

Technologically-aided survival is effectually the easiest option in this case, @Vertigo, and is the route I'm currently going down as I write. But I still need to justify giant, long-lasting storms, as they play an important part in the plot, and there needs to be a bit of land/solid surface on where to live (another part of the plot demands it). Underwater habitation wouldn't do for this story, I think.

I'll be posting the first chapter of this WiP over in critiques soon, so keep an eye out (although the planet's nature won't be really explored yet).

Good brainstorming so far guys (pun intended).

 

[psychotick]

Hi,

Don't know that the mountains have to be that large. Give the sun a slightly different light spectrum so it blasts out some infra red and the mountains will cook even through cloud layers. But even if you don't do that the mountains heating and cooling adds irregularity to the storm, so it's calmer in different places at different times, but shortly after that gets wild again.

Cheers, Greg.

 

[Venusian Broon]

All good ideas. @Venusian Broon, I've been reading up some more, and the tidal-lock seems like a good choice (great link, btw) if I don't want a 95% water surface. I would have to figure out planet revolutions and rotation speed around the not-so-hot central star. It would need to be hot enough to evaporate liquids though, with rotation fast enough to move air currents and create permanent jet streams (is that even possible in tidal-locked planets?). A problem would be that constant sun exposure on one side would also create a runaway greenhouse effect IMO. And if the dark side solidifies its atmosphere, there would be no exchange of air masses between lit and dark sides. I'd have to engineer temperature fluctuations very carefully.

Planet revolutions are linked to the orbit - you can have weird ones, but if it was fully tidally locked then the planet makes one revolution every orbit of the star. Actually that's relatively easy to work out once you've decided the output of your star (basic astrophysics), you then find the habitable zone - the distance from the star where the temperature supports liquid water (again basic) - then this radius gives you the orbital period of a planet in this spot (Kepler's third law). All pretty easy to do, I've got it in a spreadsheet somewhere with all the equations...I wouldn't have the star too small either - having a planet much too close and then you start to interfere with the star's own atmosphere - making it very, very easy for the atmosphere of the planet to be stripped away by solar winds.

Thus with a relatively long orbit I wouldn't expect the resultant rotation therefore to have much impact on the weather - however the essential mechanism that will drive the air currents on a tidally locked world is exactly the same one that drives Earth's weather - namely the sun shines on the equatorial zone and causing air to heat up, rise and set up a flow - and the colder air near the surface further away is attracted by the partial drop in pressure and rushes in, which in turn heats up and so it goes on. (Probably setting up a series of cells, like on the Earth, I'd guess.) So an air current will be set up. You won't have any jet streams as such, because you don't have a Coriolis effect in this case, or the rotation is so slow as perhaps to make it non-existent.

I remember seeing a television program where someone had modelled the atmosphere of such a planet and believe me, there definitely were air currents produced and a full planet atmosphere is definitely viable!

The temperature gradient between the two streams of air - the hot air produced by a very hot spot on the planet surface and the cold air (which could be coming in from the dark side and be relatively moist if the hot air initially flowing into the dark side is causing some surface evaporation) - could be huge. Cracking massive storms all the time. Plus as the hot spot is permanently, this process could be very quick, causing very violent winds. Possibly - I ain't no Xeno-meterologist. This mixing of the whole planet's atmosphere gives you the reason why there won't be any permanent freezing of the atmosphere on the 'dark sport' as heat is being transferred from one side of the planet to other.

I don't see how just having a constant sun exposure on one side would definitely create a greenhouse effect, I mean the sun constantly shines on the Earth, it is a number of other factors such as atmospheric gas content that stops the earth going into a runaway greenhouse effect. If your planet's atmosphere is being mixed all the time then the temperature of the hot spot will be somewhat lower anyway.

Anyway just some thoughts.

 

[Ihe]

So many things to think about and factor in! Good point on the runaway greenhouse effect, but in my defence, this could happen if the planet was mostly water (boiling the oceans, putting all the vapour into the atmosphere, thus making the atmosphere less dense, making it expand away from gravitic pull by way of overheating the surface for added heat, etc.). Eventually the atmosphere could escape the planet. But I was assuming a watery planet (I kinda confused and mixed the ideas of water-world and tidal lock. My bad.

Now that I think about it, the thing with tidal lock is that rotation is very slow, probably not enough to maintain an electromagnetic field to protect the surface from deadly radiation. The atmosphere would have to be very dense to protect humans, but at the same time, no EM shield makes the atmosphere escape faster by way of overheating and splitting air molecules into lighter ones that wander off into space. But yeah, you're probably right. A low-yield star might not have the strength to pull all of that off. Sorry, I just over-worry about getting the details right, falling short of number-crunching (as I'd be making a fool of myself).

 

[Venusian Broon]

Now that I think about it, the thing with tidal lock is that rotation is very slow, probably not enough to maintain an electromagnetic field to protect the surface from deadly radiation.

Jury seems out on this point (to a degree I admit). Mercury with a rotation of 59 days - which should be far too long to generate a magnetic field - however in fact does, although only about 1% of the Earths. However part of the reason they think it is so low is because they think most of Mercury is now mostly solid. A larger planet with a more liquid core may be able to generate a bigger effect, and other factors other than the rotation will cause the core to produce a magnetic field - I'd expect it to respond to whatever the star is throwing out its way, so it will be more transient and less steady eddy...

So you should still be able to shoe-horn some sort of magnetic field effect if you wanted

Added to that the output of the star will be less intense, being smaller, will help as you state...

I'd probably expect the planet to struggle to be amazingly wet though - especially if its been in orbit for a long time - as you say there will likely be a 'mars' effect where water is lost to solar winds eventually over time. Although that could depend on the size of the planet. A big planet with lots of mass will keep a lot of its interesting atmosphere closer to it.

If on the other hand this is a young system/planet there might be hundreds of millions of years till you start to seriously run out of water! (Not much time for alien life to evolve though...)

oh, so many variables to think about!

 

[Vertigo]

I'd agree with VB in that our magnetic field is not thought to be purely due to our planets rotation:

Differences in temperature, pressure and composition within the outer core cause convection currents in the molten metal as cool, dense matter sinks whilst warm, less dense matter rises. The Coriolis force, resulting from the Earth’s spin, also causes swirling whirlpools.

This would suggest that a tidally locked planet could have a magnetic field as in the case of Mercury. And in the case of Mercury it would probably have had a larger field when it was younger and hotter internally.

 

[Ihe]

Convection could keep the core moving, but without rotation I'm still not sure if the magnetic field would be enough to be practical. If the planet were young, it could provisionally circumvent the problem indeed, but it's true that life wouldn't have had time to evolve (and this is another necessary plot demand. Sorry to keep springing these obstacles on you guys). There needs to be a pocket of habitability and evolution.

Aaaaand more factors to take into account: if the storm is supposed to be a big mean phenomenom, it'll have strong winds (as is the case of a tidal-locked planet). If I want the planet to be habitable, then the atmospheric pressure will have to be low, so as to not rip through the surface at 300 k/h with tightly compacted and heavy winds (Mars' 200 k/h gales and storms can barely lift a kite because of its very low pressure winds---despite what "The Martian" would have us believe). The problem with this is that both high-pressure winds and very low-pressure winds would make life unsustainable without heavy "technologization". Much to think about.

I'll try to strike a balance so as to make life possible. Judging from what we've see here, I'll concoct some rough idea of the atmosphere and weather once I decide on: atmospheric density, wind mechanics, planet size/gravity, surface composition, its star's influence, and rotation speed (no matter how little). All I'm looking for is to avoid contradictions in the physics of it all. If you guys think there are other factors to take into account, let me know.

 

[Piousflea84]

My $0.02:

- IIRC, there is a mathematical theory that says that a spherical-shaped object cannot be 100% covered with wind, there will always exist a point with zero wind speed. The air has to rotate around something - therefore any storm, no matter how powerful, will have a calm "eye of the storm". True fact!

- A tidally locked planet is completely plausible. In fact, around any sufficiently dim star (red dwarfs), the habitable zone of the star is so small that any habitable-temperature planet must be tidally locked. In order to maintain a habitable temperature, that planet would require extremely strong winds to distribute heat from the "bright side" to the "dark side". In order to keep things reasonable, you probably want Earth-like or higher atmospheric pressures; a thin Mars-like atmosphere would not carry enough heat to even things out.

The life forms that would evolve on such a planet would be quite remarkable, as there would be two completely different biomes - the "light side" organisms with photosynthesis and high-temperature adaptations, and the "dark side" organisms with lower temperature and a complete lack of sunlight. Dark side organisms would likely congregate around geothermal springs and volcanic vents, as they would be the main source of energy in the absence of light.

- If you don't require an all-day-and-all-night storm but just a really powerful weather system, you could set things on an Earth-like moon of a supra-Jovian gas giant. If the moon passes through different radiation belts of the host gas giant, each transit could change the atmospheric temperature and density in a very dramatic fashion. In order to allow for life, your moon would require an anomalously strong magnetic field, so that the radiation doesn't penetrate to the surface or even to the lower levels of the atmosphere where it could strip away the air.

- If you want to be less extreme with planetary characteristics and storm intensity, just make your planet very warm and wet. Storm systems on Earth intensify when they are over warm water and lose strength over cold water or dry land. A warmer and wetter Earth (like, say, Earth 100 years from now) would have proportionally stronger weather systems.

 

[Ihe]

Quite useful, thank you.

In order to allow for life, your moon would require an anomalously strong magnetic field, so that the radiation doesn't penetrate to the surface or even to the lower levels of the atmosphere where it could strip away the air.

This wouldn't be compatible with a tidal-locked planet though, would it? As I understand it, strong magnetic fields need intense rotation speeds to be generated, something that cannot be achieved in tidal lock. As was discussed before, this wouldn't be a problem for a young planet with a more liquid core, maybe, but my planet is old enough to have evolved life. Then again, revolving around a low-yield star would make a strong mag-field NOT a priority. Also, a fast rotation will increment Coriolis effects and hurry jet streams along, which will be helpful for storm-making, but then there'd be no tidal lock. And with fast rotation, equatorial atmospheric bulging will also need to be addressed. Ugggghh.

In order to keep things reasonable, you probably want Earth-like or higher atmospheric pressures; a thin Mars-like atmosphere would not carry enough heat to even things out.

If I don't want the ground being ripped apart by winds and making any story plot impossible, I'll have to make pressure similar to Earth's.

 

[Piousflea84]

Quite useful, thank you.


This wouldn't be compatible with a tidal-locked planet though, would it? As I understand it, strong magnetic fields need intense rotation speeds to be generated, something that cannot be achieved in tidal lock. As was discussed before, this wouldn't be a problem for a young planet with a more liquid core, maybe, but my planet is old enough to have evolved life. Then again, revolving around a low-yield star would make a strong mag-field NOT a priority. Also, a fast rotation will increment Coriolis effects and hurry jet streams along, which will be helpful for storm-making, but then there'd be no tidal lock. And with fast rotation, equatorial atmospheric bulging will also need to be addressed. Ugggghh.

Rotational speed is not the only factor that plays into magnetic field generation. For example, Mercury has a magnetic field while Mars doesn't, despite the fact that Mercury rotates 50 times slower. It's possible that some planets simply have a more efficient internal dynamo.

Also, a gas giant moon would be additionally perturbed by tidal friction from all of the other moons around it. This could provide a source of heat for the planet's core, enhancing its magnetic field. (This is purely speculative - the gas giant moons in our Solar System are small and cold so they don't have a good internal dynamo, Ganymede is the only one with a magnetic field and it is very weak)

If I don't want the ground being ripped apart by winds and making any story plot impossible, I'll have to make pressure similar to Earth's.

What makes you think that the ground would be ripped apart? If a planet's energy balance requires a 150-petawatt heat transfer from the sunny side to the dark side, the amount of wind damage should (IMO) be pretty similar regardless of whether it had a 1-atmosphere surface pressure or a 100-atmosphere surface pressure. The former might require continuous 250-kph winds, the latter might require 25-kph winds. The total energy transfer would be the same, so the amount of wind erosion *should* be similar. The only way that you'd get less wind damage is if the atmosphere is too thin to transfer the whole 150 petawatts.

 

[Ihe]

For example, Mercury has a magnetic field

I think someone has mentioned that it does have, but like at 1% of that of Earth's. But yeah, I could just make the core extremely efficient and do away with complicated workarounds. Moons' volcanic activity could also contribute to the overall magnetosphere of the planet, like Io does with Jupiter. Little by little the picture is coming together, the more I read.

What makes you think that the ground would be ripped apart?

Well, the way I saw it was: thin atmospheres can hit very weakly, even if going at 200+ km/h, like Mars. Thick atmospheres will naturally have higher atmospheric pressure because of its mass and will therefore compress gases tighter together and hit harder. An atmosphere thick as syrup, going at 200km/h could do a lot of damage. But I get what you're saying. The thicker the atmosphere, the more effective the heat transfer (and I assume many more convection cells to spread chaos on my lovely world?), so less wind speeds would be needed to achieve it. My goodness all of this is so fine-tuned. If one factor changes, all of them change.