Any amateur or professional astronomers or geologists who can help me?

[sengmeng]

In currently brainstorming for a new campaign setting, and although it's a fantasy type setting, I want the planet to be somewhat scientifically plausible. At the very least, if I have to handwave a bunch of stuff, I want to know I'm doing it. My idea was a roughly earth size planet so basic things like gravity can be taken for granted, but its going to have an extreme tilt on its axis, like Uranus. The important parts of the story take place on a continent that surrounds one of the poles; magnetic north will be the center. Summer solstice will be when the north pole is pointed directly at the sun, which would seem motionless for a day or so and then it would appear to move in a gradually widening spiral until it dips below the horizon and isn't seen again until a bit after the spring eqinox. So most of the population overwinters in geological hotspots because the temperature could drop close to -100 Fahrenheit during the 4+ months of total darkness. But that seems a little too extreme, so I was wondering how different the orbit could be from Earth's to shorten the sunless winter, or perhaps some other meteorological or geological explanation for evening out the temperature extremes so that it's a more manageable Minnesota-like winter low of -30 instead.

[TheStranger]

Okay, so I'm not an astronomer, geologist, or climatologist. But my initial thought is that you need to not only warm up your winters, but cool off your summers. The summers might be worse than the winters, actually. So you need to even out the extremes in both directions. My thinking on that is that you might be able to get there with an increased greenhouse effect to spread heat more evenly across the globe. Larger oceans could also help moderate temperature, but I think less than the greenhouse effect. With the increased greenhouse effect, you'll probably need weaker solar input overall to keep the average temperature in the temperate range. I have no idea whether the science on that would actually work, or how far you'd have to take it before it did, but it's at least something to say while you handwave. How you have that much greenhouse effect without too much cloud cover to see the spiraling sunset is left as an exercise for the reader.

Another option would be to embrace the extremes but have some localized areas that are survivable, building on your hotspot idea. So at any given time, the vast majority of the continent is uninhabitable, but the population is nomadic and moves among localized temperate areas throughout the year.

Regardless, I would expect some truly catastrophic weather as the seasons change.

[martixy]

What you will get with such an arrangement in habitable zone energy levels is very, very extreme weather.

Since hot tends go to towards cold, when you put hot and cold together on the scale of planets, the equalization effect will result in quite extreme localized weather. Like, at the day/night terminators(that's the boundaries that separate day and night on the planet) you will most likely have constant hurricanes. Think jupiter's great red spot.

And parts of the year will have to normal day-night cycles, and parts will have prolonged days/nights due to extreme axial tilt. Though amusingly, if you still consider north-south based on the rotational axis of the planet, the sun's travel will still be mostly east-west oriented during the time there is a daily day/night cycle. Actually on Earth, at a constant time every day, the sun traces a path called an analemma over the course of a year. In your planet the analemma will be so extreme, it probably won't even look like a closed loop, but a cross with bent ends(the loop would only be closing beyond the horizon).

More oceans will definitely create a greater heat convection current, equalizing temperatures across the globe further than a land-dominated planet. Also more extreme weather, since more energy will constantly be moving from one place to another.

[brian 333]

We had a thread about a tidally locked world not so long ago, but I cannot find it. However, much of the same things apply. More oceans will moderate the weather extremes, while more land will magnify them.

Essentially, there will be a hotspot under the sun-side and a cold spot in the shadow side. This will cause a huge convection current of hot moist air to try to wedge under the cold, dry air at the opposite end, creating thunderstorms of incredible violence all around the perimiter of the dark/light zone.

[sengmeng]

Thanks all for answers! I had already mostly decided that there didn't have to be anything but ocean on the rest of the planet, but I should mention also that the continent is ringed by a nearly impassable mountain range, so the main story takes place in a bowl-like valley with the lowest elevation at the center, with a salty boiling swamp in the center (basically the caldera of a supervolcano). The mountains would stop a lot of the hurricanes, or at least cause them to dump their precipitation on the leeward slopes (flooding would be catastrophic every spring, but hey this place isn't supposed to be for vacations). I realize that some parts of the planet would have a regular day/night cycle for oart of the year, but none of the story will take place there.

[martixy]

I realize that some parts of the planet would have a regular day/night cycle for part of the year, but none of the story will take place there.

Depending on the axial tilt(e.g. if not exactly 90 degrees), all parts, except a small vicinity of the poles of the planet will, at some point in the year, have something close to a regular day/night cycle.

[sengmeng]

Depending on the axial tilt(e.g. if not exactly 90 degrees), all parts, except a small vicinity of the poles of the planet will, at some point in the year, have something close to a regular day/night cycle.

I am thinking 90 degrees or so close that it's hard to tell, and I've revised the idea of the "continent" to be more like a subcontinent (about 1750 miles across, about the distance between Austin, Texas and New York City).

[TheStranger]

Thanks all for answers! I had already mostly decided that there didn't have to be anything but ocean on the rest of the planet, but I should mention also that the continent is ringed by a nearly impassable mountain range, so the main story takes place in a bowl-like valley with the lowest elevation at the center, with a salty boiling swamp in the center (basically the caldera of a supervolcano). The mountains would stop a lot of the hurricanes, or at least cause them to dump their precipitation on the leeward slopes (flooding would be catastrophic every spring, but hey this place isn't supposed to be for vacations). I realize that some parts of the planet would have a regular day/night cycle for oart of the year, but none of the story will take place there.

Being in a valley like that is going to have a significant effect on the climate, most notably a rain shadow from all directions. That's potentially a big deal, as similar topography defines the Atacama Desert, where it virtually never rains. It will also reduce the extent to which the ocean mitigates the extreme summer and winter temperatures, and a dry climate will make the extremes even worse. The geothermal activity will help in the winter, but summers would be lethal - certainly hotter than anywhere on earth. You might be able to offset that a little bit if you say that the supervolcano generates enough heat to cause a near-constant upwelling of warm air from the valley that pulls in cooler air from the mountain passes, but then you're even colder in the winter. This is where you get into territory that you probably need to handwave, I think. Even so, most people and animals would migrate between higher elevations in summer and as close to the hot spots as possible in winter.

As you said, flooding from snowmelt will be catastrophic in the spring and early summer, even with the mountains limiting precipitation in the interior. How does the valley drain? I think you'll have too much snowmelt for a purely endorheic basin - you might consider some kind of Grand Canyon analogue that takes the overflow to the ocean in the spring. That would make the swamp sulfuric rather than salty, and diluted during high runoff, but the net effect is the same - you wouldn't want to drink it.

Also, 1750 miles is pretty big, I'm not sure I'd call it a subcontinent. That's only slightly smaller than Europe. Which is fine if that's what you're going for, but it's not small. If I were you I'd work backwards - how many political entities do you want to have in this valley, and how many days' travel between them?

[sengmeng]

Being in a valley like that is going to have a significant effect on the climate, most notably a rain shadow from all directions. That's potentially a big deal, as similar topography defines the Atacama Desert, where it virtually never rains. It will also reduce the extent to which the ocean mitigates the extreme summer and winter temperatures, and a dry climate will make the extremes even worse. The geothermal activity will help in the winter, but summers would be lethal - certainly hotter than anywhere on earth. You might be able to offset that a little bit if you say that the supervolcano generates enough heat to cause a near-constant upwelling of warm air from the valley that pulls in cooler air from the mountain passes, but then you're even colder in the winter. This is where you get into territory that you probably need to handwave, I think. Even so, most people and animals would migrate between higher elevations in summer and as close to the hot spots as possible in winter.

As you said, flooding from snowmelt will be catastrophic in the spring and early summer, even with the mountains limiting precipitation in the interior. How does the valley drain? I think you'll have too much snowmelt for a purely endorheic basin - you might consider some kind of Grand Canyon analogue that takes the overflow to the ocean in the spring. That would make the swamp sulfuric rather than salty, and diluted during high runoff, but the net effect is the same - you wouldn't want to drink it.

Also, 1750 miles is pretty big, I'm not sure I'd call it a subcontinent. That's only slightly smaller than Europe. Which is fine if that's what you're going for, but it's not small. If I were you I'd work backwards - how many political entities do you want to have in this valley, and how many days' travel between them?

I did the math shortly after posting and realized that it would have an area just slightly smaller than Australia, so yes, a small continent but hardly small enough to not be called one. I was thinking that the star it orbits could be dimmer, so that while the temperature range on the continent might be extreme, it would still top out at 100 degrees Fahrenheit in the summer; it's the winter low I'm really concerned with. What if it was too cold for orthogenic rainfall to be much of an issue? I'm not sure how it happens scientifically, but those of us from Minnesota know that "too cold to snow" is a real thing; at about -20 and lower, there doesn't seem to be any clouds or possibility of precipitation. Maybe water could blow over the valley as ice crystals and turn to rain as it hits the warm air from the geothermal activity? Also, water would tend to be trapped in the valley; I'm picturing the central lake/sea/swamp putting off so much steam that it's almost in stasis with the inflowing rivers. Any water making it back to the ocean would be through caves.

[brian 333]

Look at the Okavango Delta in Africa. Billions of tons of water dump into it and vanish into the desert sands every year.

Imagine: The winter becomes bitterly cold and survival depends upon proximity to thermal vents within the encircling mountains. At -20 degrees the outside becomes uninhabitable except for cold-type creatures, and temps drop to as low as -100.

Small creatures burrow and hibernate through the cold, but large herbivores and their non-hibernating carnivores require the ravines where hot-springs create hot pools and streams around which they can cluster and forage for food. Like the penguins, they share warmth by huddling into dense herds, sometimes composed of a mix of herbivore types.

With the first light of dawn the herbivores begin calving, and as the day-night cycle begins the warmth proceeds, and the cold-dependant species retreat into high altitude and glacial environments to sweat out the coming heat while burrowing creatures begin to come out with the first greening.

Rainstorms begin. Harsh, lashing thunderstorms which often conclude with heavy, wet snow soon give way to storms which make the Indian monsoons appear tame. Huge volumes of water wash down the gullies into valleys which are still under ice, which floats into the central bowl of the continent forming a vast inland sea choked with ice floes and sediment laden runoff. This creates a very fertile environment for algae, which coincidentally is perfect timing for the fish which, through a variety of strategies, survived winter and now explode in population booms.

On land, this produces a similar bloom of plant life which has a very fast growth cycle, which nourishes the herbivore herds. The herds follow the green, and the carnivores follow the herds as they move out of the shelter at the feet of the mountains and onto the plains.

When the sun has climbed about halfway into the sky and the ever-shorter nights give way to endless day the rains are few and far less violent. The mass of water which flooded the inland shallow sea now begins to evaporate. This pushes humidity up into the high 90s, (F,) which prevents ground temperatures from reaching 100 because at this point summer showers fall in hot, fat raindrops which cool off the region for a short time before blowing away, leaving thick, oppressive humidity, which again begins build up to another summer shower. This is the time of maximum growth for the plants.

When the sun is about three quarters of the way up the last summer rains are scattered and blow away quickly, allowing the lands above the sea to begin drying out. The seashore begins to retreat as the sun bakes the land, but the mud which nourished the lake early on now nourishes water-grasses, reeds, and many kinds of plants. The herds follow the retreat of the seashore as temperatures begin to rise up to 120 degrees.

At this point creatures of the heat types begin to emerge from their lairs in geothermal regions as the herbivores and their carnivores encircle the dwindling sea. Many small creatures, having spent the green time gathering mounds of grass and seeds, now retreat to the underground coolness, relying upon their larders to get them through the heat.

When the sun is straight up the intense heat evaporates the sea at such a rapid pace that massive clouds build up blocking much of its light, preventing temperatures from exceeding 120 degrees by much or for very long durations. Rain at this time is uncommon, and the sea continues to evaporate fast enough to maintain the cloud cover.

When the sun is over halfway back to the horizon the day-night cycle begins again and though the heat remains oppressive, humans can move about without dying of heat stroke. This is when the rains begin again, but they are somewhat mitigated by the dryness of the air. Most of the cloud cover which was formed by the evaporating sea gets blown away. A second greening occurs, and herbivores migrate out of what has now become a mineral-laden sea less than half the diameter of its springtime glory. Salt pans are exposed and are divided by small, grass-covered islands, but the sweet water which is now running down the mountain streams lure the herbivores back into the foothills as the heat-type monsters seek warmth.

As the days grow shorter the first winter snows blow through, and small critters hoard their winter caches while large herbivores mate and grow winter coats.

Note that this model assumes an equatorial continent as opposed to a polar one. This maximizes the length of the seasons between the temperature extremes and minimizes the times of the extremes. A two month winter and summer extreme is divided by a four month spring and fall. The farther one goes toward the poles, the longer, and more extreme, the extreme times.

[aimlessPolymath]

Wow, my major is actually relevant!
Amateur geologist here, and what you're describing are Milankovitch cycles. Specifically, there are three factors that control how Earth's orbit affects the distribution of sunlight.
You've messed around with obliquity (axial tilt), settting it very high, but we can partially offset it using eccentricity, which is a measurement of how round the orbit is- specifically, high eccentricity means that one axis of orbit is longer.



Ignoring the cyclic nature of this factor for a moment, we see that we can have "summer" be during a time when the earth is far away from the sun, and "winter" be during a time when it is very close.

This leaves only one side of the planet inhabitable- the other side will see much intensified summers and winters.

[Amblehook]

...we can partially offset it using eccentricity, which is a measurement of how round the orbit is- specifically, high eccentricity means that one axis of orbit is longer.



Ignoring the cyclic nature of this factor for a moment, we see that we can have "summer" be during a time when the earth is far away from the sun, and "winter" be during a time when it is very close.

This leaves only one side of the planet inhabitable- the other side will see much intensified summers and winters.

This is exactly what I was going to suggest. If you adjust the eccentricity enough, not only can you lower the solar energy reaching one of the poles (the one you'll have inhabited) by having it further away from its sun during that pole's summer, but its winter will be much abbreviated, as the planet moves much more quickly (with a large enough eccentricity) through that part of its orbit.

[sengmeng]

I hadn't checked this thread in a while, but the last two posts are very intriguing; I think with a perfectly oblique axial tilt (glad to have the right terms too) and the eccentric orbit, plus perhaps a closer orbit to a smaller dimmer star, it could have an overall year about 8 earth months long, with summer about 5 of those months and fall (twilight), winter (night), and spring (dawn) each only a month long, and otherwise very Earthlike (or at least only as bad as my lovely home state). Also, the tides would destroy anything not protected by Himalaya-like mountains. Thanks!

[brian 333]

Remember to account for precession. Spinning spheroids wobble.

Also, most elliptical orbits trace out a spirograph. This leads inevitably to each pole being closest to the sun during summer and, eventually, farthest. The question is, how many years before the pole comes back under the sun at its closest point in the ellipse. This could be years, decades, centuries, eons, or even longer, but it would be cyclical.