The Problem

In a world I am building, the days are 9 years long, this means 4 and half years of cold darkness following 4 and a half years of blistering daylight. I have asked questions on this Year long Day world before, but now I have a new thought on the night side.

In an environment with little light (the planet has a ring) and heat (there are active volcanoes), could life exist? The previous assumptions on this topic were divided between two schools of thought:

  1. Certain lifeforms on the day half would lay eggs that would remain insulated throughout the night and hatch when day arrives and that creatures would evolve ways to survive the night so that they could eat these eggs.
  2. Life would be unable to survive without sources of light and little plants for producers.

This wouldn't be a problem if not for the fact that there are good arguments for both sides.

The Question(s)

  1. Could animals evolve to live in such a harsh environment in the same way that in could on the day side?
  2. If animals could exist on the night side, how would they survive, with the lack of vegetation, light and heat?
  3. If an animal from the day side were to get caught in the night, could it survive and for how long?
  • $\begingroup$ Your biggest problem with 4.5 years of darkness is the death of all the vegetation. On earth ocean algae and large forests are responsible for cleaning the air and producing oxygen. If it's all dead, how does anything breathe? The air would become toxic very quickly. $\endgroup$ – Steve Mangiameli Oct 4 '16 at 21:18
  • $\begingroup$ @SteveMangiameli vegetation florishes much more on the day side, think jungles everywhere. Plus there are massive oceans at the poles where the night isn't as long $\endgroup$ – TrEs-2b Oct 4 '16 at 21:25
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    $\begingroup$ @a4android the dusk/dawn areas (give or take a few kilometers depending on environmental conditions) are filled with hurricanes, think Jupiters red spot, but a line $\endgroup$ – TrEs-2b Oct 5 '16 at 4:41
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    $\begingroup$ You don't have to go all that deep into an ocean before days and seasons don't matter. Life on the seafloor is more driven by plate tectonics than the planet's host star. I believe that environment is considered to be somewhere that life on Earth might have started, but don't quote me on that. $\endgroup$ – ktyldev Oct 5 '16 at 16:21
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    $\begingroup$ If one half of the world is dark, the other is light, and they shift very, very slowly, couldn't a species just live in the habitable zone between dark and light, then migrate over the course of years? @TrEs-2b $\endgroup$ – Zxyrra Oct 17 '16 at 9:56

I do not believe life could evolve under such conditions but I see no reason to think the world would need to be lifeless.

  • Plants. There are two survival options here:
    1. We have a very common class of plant that needs little tweaking to survive this. We call them annuals. They live during the warm time, produce seeds and die. Those seeds bring about the next generation in the next warm time. Your warm and cold times last a lot longer but it's the same basic idea.
    2. Some plants can survive the total freezing of the plant structure during their dormant period. Such plants could survive your long winter.
  • Animals. Here the choices are far more limited.
    1. Hibernation. By itself this is almost certainly not enough. The body uses too much energy while hibernating, a hibernation period that long is probably not possible.
    2. Freezing. There are animals that survive extreme cold by totally freezing. Life processes stop, the energy use during hibernation is not an issue. When things warm up they thaw and go back to living.
    3. I'm not aware of any examples but I would think an overwintering egg would be a possibility. The fertilized ovum would not start to grow until it had been through a freeze-thaw cycle.
    4. Conceivably there could be a critter that survived by stockpiled food. The needed stockpile would be huge, though, and quite a temptation to raiders of various sorts. I doubt it would be a viable life strategy.
    5. Assuming a geography that tolerates it the animals could simply be in a permanent migration. Walking around a planet in 9 years is something any larger animal could do if they weren't confronted with impassible terrain.
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    $\begingroup$ Like the idea of permanently migrating animals, if assume them living on the equator of an Earth-sized planet they only need to walk about six miles per day to maintain a constant climate. The large oceans could get in the way, but animals adapted to both land and the seas isn't implausible. $\endgroup$ – a4android Oct 5 '16 at 5:10
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    $\begingroup$ About overwintering eggs: locust eggs will only "ripen" and hatch once humidity rises above a certain level and when conditions are right for locusts to emerge and forage for food. There is a patch on the surface of the egg that responds to humidity. Almost like a sensor mechanism. Overwintering eggs are a distinct possibility in that case. $\endgroup$ – a4android Oct 5 '16 at 5:15
  • $\begingroup$ @a4android Timed hatching wouldn't be a problem, I was more concerned about surviving the winter. When the egg matter freezes it's going to cause a big problem for it's shell. $\endgroup$ – Loren Pechtel Oct 5 '16 at 5:18
  • $\begingroup$ That's what I liked about the overwintering egg idea. Locust eggs hatch when external conditions are right. An equivalent example. The eggshells might be flexible enough to allow for expansion during the freezing phase, then become inflexible and rigid when the freezing is complete. Surviving the long winter is an interesting problem. $\endgroup$ – a4android Oct 5 '16 at 5:45

Ocean vent communities exist with no light, as do microorganisms in deep rock, so the answer is an obvious yes, as long as that life is part of a chemosynthetic food chain. See also speculation about life in Europa's ocean, many (60?) miles under the surface ice.

For life based on a photosynthetic food chain, consider the Earth's deep ocean as a model. Many animals live in the deep ocean (benthic) zone, getting their food supply from dead organisms & wastes that drift down from the surface. A "whale fall" can sustain a deep ocean community for decades (per NOAA: http://oceanservice.noaa.gov/facts/whale-fall.html )

So assuming your planet has a world-spanning ocean, like Earth, marine life could be based on a migrating photosynthetic zone that follows the sunrise and sunset around the world. Some animals - fish, whales, birds like the albatross - could follow the zone, other life could inhabit the deep ocean, depending on fallen detritus produced during the photosynthetic 'spring' and 'fall' for survival.

Given that basis, it's not too hard to imagine some of the ocean life evolving to exploit new niches on land. One could likewise imagine animals evolving to be migratory: a human could walk around the Earth (given a suitable path - no oceans in the way or similar obstacles) in 9 years.


First of all, I loved the idea. So lets think about life on a planet which had a day night cycle of 9 years.

The main issue with 4.5 year night is energy. Even you hibernate, it is extremely hard for a creature to stay alive under harsh conditions. But that doesn't necessarily means there is can't be life on that planet;

I imagine there would be islands of vegetations, which can move slowly to keep in the day side, moving west as planet rotates. To stay alive, those giant islands of living plants would need to form a mutualist relationship with each other, for example I imagine them carrying their water source with them. Because of such harsh conditions and temperature difference, I would guess the planet is a sand planet, and the vegetation islands are moving extremely slowly on this sand sea, to always stay under the sun. The animals, on the other hand has to live and move between those islands. Water is very precious in such environment since on day side, the sun always shines. I would imagine there to be vegetation traps like giant venus flyeaters to protect water from others.

Even though it is not the only reason, the temperature change is one of the main reasons for wind as far as I know. The atmosphere of such planet would be windy. Any intelligent life form would be primative since metal is hard to find and staying in same place would mean death but they may use wind to gather energy (not our kind of giant metal wind mills but like ones in miyazaki's nausicaa). Such intelligent creatures would have a rich culture with appreciation to plants and other creatures.

I guess evolution would create creatures who prefer night side too. The living islands would leave a trail of waste as they move and night side creatures would "clean" the waste creating some kind of cycle as we have in earth.


Migrating and/or hibernating plants and animal life could easily develop on such a planet. Laying eggs for the night and hatching on day time is also possible, but migration is slightly easier. Your photosyntetic life forms could very well be mobile, or short lived so they keep spreading to the daytime zone. To make things easier, you could have a continent that runs through the entire planet. Thus, this rapid spreading would easily work. If this does not work for you, your planet would be dominated by the flying animals and plants. If it means they would get day time for their entire life, plants might develop flight.


I was thinking about this some more after a few questions and answers. Everyone assumes life forms would be living, in their entirety, on the surface of the planet. While I think this is a rational argument for most of the plant life, it doesn't need to be necessarily true for the animals.

What if there was a whole other ecosystem that developed under the surface? Nutrient rich algaes/lichens to entice herb and omnivores into vast underground caves, which then entice the carnivores.

Plants on the surface can follow the annual and hybernation models found on earth. Plants under the surface are more like algaes and lichens that thrive more on heat than light.

All animals have a pseudo hybernation wherein they sleep for long periods of time, waking only to feed for a few days/weeks to rebuild stores and go back to sleep.


I'm thinking of reptiles that shed their skins. During the months-long "dusk" on your planet, animals grow a thick protective layer that will prevent heat loss and shield them from harsh conditions during the long night. During the "dawn", they could shed it.

In addition, like squirrels they could store food during the day that they would eat during the night.

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    $\begingroup$ What are they eating? Plant life would be dead shortly after sunset. $\endgroup$ – rek Oct 5 '16 at 1:08
  • $\begingroup$ @rek They are eating the food they stored during the day like squirrels. Stuff like seeds and nuts. $\endgroup$ – a4android Oct 5 '16 at 5:03
  • $\begingroup$ So only a single species survives the night? $\endgroup$ – rek Oct 5 '16 at 12:21
  • $\begingroup$ @rek Not sure. This is just one approach. $\endgroup$ – BrettFromLA Oct 5 '16 at 17:12

I see also very big problems on the day-side. I think that it will be very hot after very short time. Maybe the life will happen mostly around the day/night-line where it could be not to hot and not to cold. You could also change this by winds, e.g. warm winds that flow to the night-side and warming it.


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