View Full Version : Permanent day and night

The Insanity
2014-10-21, 08:23 AM
I'm thinking about making a game in a setting where one side of the planet is permanently facing the sun. I'm wondering what effect would the lack of night/day have on flora, fauna, geology, etc. of the respective sides and how would they be different from each other.

2014-10-21, 08:33 AM
There's an actual scientific model for this sort of planet floating around, though I fail to remember its name. The model also included some hypothetical flora and fauna. It was a tidally locked planet orbit a red dwarf star. See if you can find it.

The big things to remember are that the side facing the sun will basically be a scorched desert, while the side facing away from the sun will be icy cold. If there's water on the planet, you can expect it to flow from the cold to warm side, turn to steam and the condense back on the way to the cold side. There will be a fairly narrow band of temperate climes between the two where life is possible. Living things will probably have something similar to a sleep cycle in reaction changes in brightness of the solar body. When the star is bright, plants open up while animals hide from excess radiation etc.

2014-10-21, 08:40 AM
Sunside is a lifeless, parched wasteland. Darkside is lifeless, frozen wasteland.

A barely-habitable band of twilight wracked by nightmarish weather may exist at the border between the two.

Jay R
2014-10-21, 09:05 AM
If it's a fantasy world, I would make the terminator (ring around the twilight area) a temperate region, with jungles in the angled sun and a big desert under the direct sun.

To the night side, there would be a thin ring of snowy forests on high mountains that just reach the sun, leading to tundra and finally an land of ice filled with magical creatures that don't need heat or light to survive.

All oceans would span the terminator, and would have glaciers on the night side and icebergs would be pretty common. Some icebergs might be inhabited.

In the middle of the desert, I would have some big impressive dungeon or something, because anything living in that area would spend most of its time underground. The desert would contain djinns, salamanders, and other creatures that can thrive in that heat.

[And I would be all too tempted to put a habitable land, split into four parts, peopled by four different races, in the center of the Deadly Desert.]

Admiral Squish
2014-10-21, 09:47 AM
I suppose the question is how earth-like is the planet in question supposed to be?

I once made a sci-fi world that orbited an o-class scar far too close for most creature's comfort. The planet's 'north' pole directly faced the star at all times, and it spun very quickly to maintain it's shape against the intense gravitational pull. It was a nightmarish world, bathed in incredibly intense UV radiation, and baking under an atmosphere of sulfuric acid and carbon dioxide, so hot the entire planet was molten down to the core, almost 2000 degrees at the 'north' pole. The only land was the 'nightland', a floating continent of volcanic rock on the 'south' pole, under an eternal hurricane created by the 'cool' air (still nearly 500 degrees) descending. The hurricane scoured the land with razor-sharp obsidian shards and sulfuric acid mists. But despite the harsh conditions, life existed. Massive, blind beasts 'swam' through the molten rock in different regions of heat and thickness, drinking in molten glass and surfacing, briefly, to release puffs of oxygen into the air, which where then absorbed and processed by floating 'plants' that bound the oxygen to silicon and secreted it into the magma again. I called it 'Gehenna'.

Anyway, bizarre digression aside, a planet being tidally locked will probably be extremely different from earth, even if all other things remain the same. It depends on the direction you want to take it.

The Insanity
2014-10-21, 10:12 AM
It's similar to Earth in everything other than the sun thing.
Lets say it wasn't always like that. Long enough for nature to adjust itself, but short enough that the planet didn't just completely melt on the day side.

2014-10-21, 11:19 AM
There was a lovely thread about this a while ago... I think it was this (http://www.giantitp.com/forums/showthread.php?146831-World-Building-Ideas-A-Tidally-Locked-World) one? Might want to browse through that for some inspiration.

2014-10-21, 11:40 AM
I don't know if a tidally locked planet would actually have a molten sun-side. The cold side of the planet would vent enough heat to keep the sun-side from melting rock. Maybe if we were dealing with a greenhouse planet like Venus, but Earth's atmosphere wouldn't hold enough heat. I think. Not an astronomer of any kind. We're definately looking at a sun-scorched desert for most of the sun-side, though- You'd definately hit 335k at least somewhere, so we're not getting any clouds or lakes. Without water, you don't get life, so you're limited to elementals on that side. The dark side runs into a similar problem- The only things on earth that aren't depending on the sun are tube-worms, and those have heat from the core to fuel their ecosystem. So, once again, no plant life. No plant life, no animals. Another desert, since I'm pretty sure you wouldn't get any perciptation at that temperature (Antarctica gets basically no perciptation because the air can't hold enough water for clouds to form).

Hmm... You could have elemental kingdoms in the hot and cold zones, although you're risking heat-miser snow-miser jokes with that.

2014-10-21, 12:00 PM
Also Pathfinder did a planet like this in their mini splat of the other planets in Golarian's system. Worth a look.

BeerMug Paladin
2014-10-21, 12:10 PM
It would probably be like other people have already suggested. One thing to consider is that things which are tidally locked tend to be denser on the side nearer to whatever they are tidally locked to. What this means is the area could have denser rocks, rocky terrain, or other such features. I'd probably place most richer mines and active volcanoes on the perpetual day side.

Also, there still could be somethng of a seasonal cycle on such a world, provided by libration (http://en.wikipedia.org/wiki/Libration). For your purposes, only the first two types of libration would matter. Essentially, the north/south strips of twilight would drift slightly in their location due to axial tilt. This means that the location of the band of light reaching the planet's surface varies by the time of year. A place could be at the edge of twilight during one part of the year, then cast in perpetual darkness the other part of the year. Or alternatively, be in the center of the band of light, then on the edge of its reach in another part of the year. How far it drifts depends on the planet's axial tilt. Places at the equator would experience less drifting of the band of twilight from this effect.

Also, since orbits are rarely perfect circles, but spin is going to be constant, there's also a east/west day/night drifting cycle depending on whether the spin is lagging behind or is ahead of the orbit. This is essentially another measure of seasonal drift, but makes the day/night band shift "east" and "west" a bit. The sizes of these two effects could be different, so that some cities go through a seasonal period of darkness and light and other cities reign in perpetual starlight with no seasonal day/night cycle.

I don't think both these effects are required to be perfectly lined up with each other over the year, but the yearly variation is probably likely to be slow enough not to matter for a game. Whether or not the bigger drifting of the zone of twilight is between east/west or north/south during the season is optional. The effect could be balanced as well. The only thing that really matters is where you decide it drifts and by how much over the planet.

Or you could ignore all this and just do whatever crazy thing you want. This is a fantasy world, after all.

2014-10-21, 03:04 PM
Sunside is a lifeless, parched wasteland. Darkside is lifeless, frozen wasteland.

A barely-habitable band of twilight wracked by nightmarish weather may exist at the border between the two.

Dungeon, huh ? ;)

2014-10-21, 03:29 PM
Dungeon, huh ? ;)

If I've made a reference to something I'm entirely unaware of it.

Anyway, a bit back on track if one wants the light side/dark side thing, without the whole thing turning into a basically unlivable nightmare world, why not abandon the whole "Planet" idea?

That is rather than modeling things in the spirit of the real universe with a rocky body orbiting an over-sized fusion reactor, one could with something a bit more outlandish. If you throw out the idea the world is a body in space following something roughly approximating our physical laws on a cosmic scale, you can introduce all kinds of dynamics without stretching suspension of disbelief.

Maybe the world itself is inherently "Cold" on one side and the god(s) created the sun to warm it, while the moon has a cooling effect on the on the naturally "Hot" other side. Being in the shade (blocking the cooling rays of the moon) even feels warmer the way being in the shade from the sun feels cooler. Obviously this just one idea. There are a lot of directions you can go in once you stop trying to be true-to-life and just kind of run wild with the premise