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I was doing some tests in Universe Sandbox a while ago and I noticed a strange behavior shown by giant planets on highly inclined orbits. In the simulation I placed an Earth at 1 AU around the Sun, and with an inclination of 0 degrees, and a Jupiter in a 2:1 resonance with Earth. The Jupiter was also at an orbital inclination of 20 degrees. When I ran the simulation, things seemed normal at first. However, I soon noticed a pattern with the Earth's movement.

In a period of around 100 years, the Earth's orbital inclination increased to around 40 degrees, then decreased again. It then continued until its orbital inclination was around -40 degrees and then increased, spanning a time of 2 centuries per cycle, which i dubbed "Inclinatory Cycles". I tested other things too. With further tests I concluded that the Earth will always deviate from its base inclination by twice the giant's inclination on each cycle, and that the higher the mass and the closer the giant, the faster the cycle.

So, I was wondering if these "Inclinatory cycles" could be used in seasonbuilding. After all, more extreme inclinations lead to more extreme seasons. I can imagine an intelligent species realizing that for half a century, the seasons get more extreme, with hotter summers and colder winters. and for the other half, they get less extreme. Seasonal floods in rivers from the melting poles during an extreme summer could be the telltale marking, and this could be used for agricultural purposes. Now, my question is: Is this setup with a highly inclined gas giant even possible, and what would be the ramifications it would have on agriculture?

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  • $\begingroup$ Two questions, and one is surely too broad. Please narrow the scope of this post. $\endgroup$
    – L.Dutch
    Sep 9, 2020 at 5:37
  • $\begingroup$ Yes, Milankovitch cycles do exist and do have a significant influence on climate. I would say that such large orbital inclinations are rather unexpected, but they are of course not impossible. $\endgroup$
    – AlexP
    Sep 9, 2020 at 6:56
  • $\begingroup$ Milankovitch cycles are caused by changing the eccentricity, not the inclination. Would they have a similar effect? $\endgroup$
    – Nip Dip
    Sep 9, 2020 at 13:34
  • $\begingroup$ "What would be the ramifications it would have on agriculture" is too broad. Do you want us to analyze Montana Winter Wheat? or Austrailian Forestry Products? It's a planet we know nothing about. What answer could anyone provide other than "intelligent inhabitants would find a way to deal with it?" Please ask one and only one question (which is SE's model: one-specific-question/one-best-answer). $\endgroup$ Sep 9, 2020 at 17:43

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You don’t even need the gas giant. It is believed that resonance effects with the moon as it recedes from the Earth can cause large fluctuations in the Earth’s axial tilt, so all you need is a planet with a large moon that’s a bit further away from it.

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  • $\begingroup$ Axial tilt and the inclination of the orbit are two different things. $\endgroup$
    – AlexP
    Sep 9, 2020 at 6:53
  • $\begingroup$ @AlexP That’s a fair point, but a large and erratic axial tilt will still give the extreme and fluctuating seasons that the questioner is looking for. $\endgroup$
    – Mike Scott
    Sep 9, 2020 at 7:05
  • $\begingroup$ @MikeScott An erratic axial tilt would produce those seasons, but axial tilt is to my understanding something that changes over thousands of years, not a few decades. It's also not what the OP asked about; I'm frankly not sure that orbital inclination has any meaningful effect on climate, but I can't speak with any certainty. $\endgroup$
    – Palarran
    Sep 9, 2020 at 20:37
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I don't see any reason why this wouldn't be possible.

As for the impact on agriculture, the people might have to do cyclical migration: moving closer to the equator when the tilt is more extreme & maybe back out when it's less extreme. The crops that the people would be able to grow would change in tune with the cycle.

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The ramifications it would have on agriculture are the same as it would have on the ecosystem in general: life would have to be adapted for such swings. (This means that any agriculture would be based on the wild things that already are adapted.)

Some plants, or even animals, might go dormant for the extreme period. (For a period this long, they are more likely to be insects in egg or pupae stage.) Others might take advantage of the extreme period to avoid the competitors and go dormant as the weather grew more even.

Migration toward and from the equators is possible. It's on a time frame such that animals (such as humans) could manage it, and even plants that grow on a short time frame by spreading their seeds wildly.

Some species might adapt to all seasons. This would probably require such things as shedding fur for animals, and ability to take both severe drought and flooding.

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