A planet in the video game Mass Effect, which had nearly toxic levels of pollen, made me think of this: Pollen tornadoes?
Actually a large proportion of terrestrial “planets” are probably moons of gas giant planets like the moons of Jupiter and Saturn. We’ve observed that supergiant planets are pretty common, and will tend to dominate their orbits, collecting together smaller planets or else kicking them out into distant resonances.
As a planet, there are good reasons to believe that the Earth is pretty special, and that a lot of what makes it special is the global biosphere that has spend more than four billion years conditioning and modifying it to a ‘just-so’ condition where free liquid water exists on the surface. Without life, the Earth would likely be a runaway greenhouse like Venus, or a frigid iceball with a thin carbon dioxide atmosphere like Mars in which surface water will evaporate and ice will sublimate unless mixed into a vapor-resistant brine.
As for the question of the o.p., I don’t think there is any limit to potential weather phenomena beyond what is physically possible. Acid tornados, silicate snowflakes, magnetically driven hurricanes…I doubt we can even scratch the surface of what unexpected phenomena we might find, especially on gas giant or brown dwarf “planets”.
Stranger
I can’t find the reference but I read speculation that at least one planet was hot enough and big enough to rain liquid iron. But what impresses me even more is the implication that there are clouds of gaseous iron on that planet. Now that is bizarre.
That would be an interesting prospect. If the Solar System is typical, moons of a gas giant would normally be significantly smaller than a terrestrial planet. But if it is possible for a gas giant to collect some of the terrestrial planets it displaces, then Earth-sized moons might be fairly frequent. After all, Neptune seems to have captured Triton at some point in the past.
Note that such a planet-sized moon would probably be tidally-locked to the planet, so would have quite a different climate to Earth (even if life existed there).
Earth-sized worlds orbiting red dwarfs would probably be tidally-locked to the local star, making the weather there very strange. A hot-spot underneath the local star, and cooler regions at the terminator, would make the weather patterns strangely persistent and possibly quite violent. A cyclone might form on one face of the planet, and ice caps form on the other face- although the circulation of the atmosphere and hydrosphere could amend hese patterns significantly.
A recent paper suggests that a planet with a severe tilt could develop icecaps around the equator- very unlike the conditions on Earth.
There supergiant planets that have been found that are more than 10 times the mass of Jupiter; much above that and you get into brown dwarf territory which could entertain a moon the size the the Earth at a distance that would not ensure tidal locking. There is also a hypothetical class of planets called chthonian planets which are gas giants whose atmospheres have been stripped away by novae and cataclysmic variable binaries, leaving a core of anything from metallosilicates to exotic phases of crystalline carbon. I’m sure we’ll eventually discover planets in configurations with unique behavior we can’t even imagine.
Stranger
Tornados, hurricanes and the cyclic weather of earth (the swirling cyclonic storm fronts) are a side effect of (a) fairly rapid rotation and (b) the corresponding Coriolis force as motion drives moving air toward the poles, which also causes the extreme weather systems that tend to dominate.
So what would weather look like on a tidally locked planet, or one (like the moon) where here is very little Coriolis force.
In Ringworld, where the artificial world is a channel 93M miles diameter spinning around a sun, Niven suggested a hole in the sidewall would result in a horizontal tornado as the air drained out the side.
Could you dig up that paper? I’m having a hard time makiing sense of that–a non-tidally-locked planet with a 0° tilt to the plane of its axis would have the minimum percentage of its surface exposed to direct overhead starlight over at least some part of the year and a planet with a 90° tilt would have the maximum–for a planet with a 90° tilt, each pole would spend part of each year in total darkness but also part of the year in maximum starlight. The equator would spend two parts of the year in “total dusk” or" todal dawn" but never the absolute midnight of the poles, and for two parts of the year, the equator would receive maximum starlight, and since the planet is rotating, all “sides” of the equator would get that maximal starlight each year. (The axis of rotation of a planet isn’t locked facing the star as it orbits.) (Having said that, the Earth itself may have been glaciated to or near the equator more than once, the last time fairly recently in geological terms.)
Here it is
I think this means that the poles would melt first after an ice age. That would also be highly dependent on the topography, of course.
Makes sense to me. Once you’ve got snow/ice coverage somewhere on a planet, that spot will tend to remain cold, because ice and snow are very reflective, and absorb comparably little energy from the sun. A pole of a highly-inclined planet will have a very long day, long enough to burn through the ice down to more absorbtive bare ground, after which that spot will remain warm. But the equator will have only normal-length days, not long enough to remove the ice before it gets replenished, and so it will stay icy.
The coolest I think are spontaneous (well, formed from lightning strikes high in the atmosphere of a large gas giant) diamond rain falling into either a liquid diamond sea, or, even cooler, a metallic hydrogen ocean. Not really weather, but I read that some of the speculation about neutron stars is that they have a brittle crust and ‘nuclear pasta’ below the surface. I just think that’s a cool concept…‘nuclear pasta’. 
Classifying weather we have on Earth very broadly, we have:
- Rain = liquid precipitation from the atmosphere
- Snow/sleet/hail/etc = solid precipitation from the atmosphere
- Lightning = electrical potential equalization
- Heat/cold = thermal variance
- Wind = atmospheric motion
- Evaporation/humidity
- Sublimation? I think it happens a bit at altitude
- Tides? Do these count as weather?
- Wildfires? = rapid oxidation
- Sandstorms = wind that picks up bits of surface solids
And, I guess, combinations of those.
Some things we don’t have that other planets could
- Other phase changes: Boiling of seas into the atmosphere, rapid sublimation planet wide, plasma <=> gas?
- Rapid reduction? Some endothermic reaction that starts and makes things colder on a broad scale. Basically the reverse of a wildfire.
- Strong tidal effects
I’ve always wondered about weather patterns on a planet tidally locked to a red dwarf.
So say you start with an Earthlike planet. The hot side gets hot, the cold side gets cold. Volatiles boil on the hot side and condense on the cold side. So the cold side develops huge glaciers, while the hot side dries out.
Eventually the cold side gets cold enough that any atmosphere freezes out onto the cold side. The hot side is barren rock, the cold side is barren ice, and there’s no atmosphere left. Weather is now finished.
I guess if you had enough volatiles that the ice is thick enough the glaciers would ooze into the equatorial zone over the millenia and boil off again and recondense again. But you’d have to have a really thick layer for this to count as weather, if there’s not enough ice then the equatorial active zone is too small. If you’ve got a water world then I guess pressure under the multikilometer thick ice sheet melts the water and it all flows out to the equator. If you don’t have enough water then pressure keeps the other volatiles frozen rather than melts them, and then there’s no weather.
iamthewalrus, you forgot to mention that the precipitation that falls on Earth is all composed of water. One of the things other planets could have that the Earth doesn’t is precipitation that isn’t water.
The top of the highest mountain already poking into outer space, in the case of Olympus Mons on Mars. However, I must defer to the experts who can perhaps give a more accurate definition of “outer space” in relation Mars, and whether or not my first sentence is correct.
Olympus Mons does not extend beyond the atmosphere. The lower gravity of Mars means the atmosphere rises higher than it would on earth. Atmospheric pressure at the peak is 12%, which is absurdly low compared to earth’s atmosphere, but it appears that stuff wafts around up there.
Fist-of-God, though, I think did extend above the atmosphere, because otherwise the Ringworld would be losing atmosphere too quickly, and were it leaking atmosphere in such close proximity to the eye storm, the ring itself would very quickly become unstable and float into or away from the star. Since one can travel to the ring using Celestia, we know it must still be there.
One thing that people forget about tidally-locked planets is that they do rotate, once a year. If the planet is in a close orbit around a particularly dim red dwarf then the orbital period inside the habitable zone is a matter of a few Earth days, possibly as short as a single Earth day.
I have seen simulations which take this rotation into account - the atmosphere is subject to Coriolis forces, just like on Earth, and the result is a kind of smearing, so that the hot air on the sunward-side is transported into the cool side, allowing temperatures to equalise.
Unfortunately I don’t have a recent cite for these simulations, although I could probably find one.
This arxiv paper by Yongyun Hu and Jun Yang has some nice diagrams that show the smearing of temperatures by rotation on a tidally-locked world; you get a strange ‘butterfly’ shaped hot spot on the sunward side that transports heat into the dark side.
On the other hand, you only get that butterfly-convection to the extent that there are still any fluids on the lit side. All volatiles frozen out on the dark side is still an equilibrium, and probably a stable one.
A gas giant with a smaller gas giant moon! Goooooolllly! What will they think up next?
Seriously, I’m just waiting for the system that is a neutron star orbiting a black hole with a captured O class supergiant star feeding it hydrogen and a bunch of smaller planets bouncing around like ping pong balls in a clothes dryer. Until you can show me that, I’m not even going to bother getting out of bed.
Stranger