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TLDR; what would weather be like with minimal axial tilt?

Included is a picture of my climate map and several perspectives of a paper model I made of the planet. The ocean covers over half the planet, which is rather small. It has nearly no tilt, and 2 moons; a bigger moon Aurie that is round but not perfectly circular which has some impact on tides but not too strong, and a smaller moon Chi which is too far and small to have a significant tidal impact. I’m thinking/hoping/praying that with a small tilt comes nearly no seasonal change, yes? Or... Is the tilt vital to life itself? And for that matter, can anybody help me figure out what the weather would be like on a planet with no axial seasons? I know I’m asking a lot, and I’m new to this site so I understand if this is removed. I’ll post an “answer” of my other terrestrial map so you can refer to the areas by name by they are in pretty obvious 4 quarters: NW, NE, SE, SW.enter image description here

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  • $\begingroup$ As you have been already explained in your other question, to add information to your own question use the edit function. Do not place an answer. $\endgroup$
    – L.Dutch ♦
    Commented Feb 16, 2019 at 8:28
  • $\begingroup$ Oops, here it is: edit when you thought that you'd lost it. $\endgroup$
    – Escaped dental patient.
    Commented Feb 16, 2019 at 8:32
  • $\begingroup$ @L.Dutch I’m 99% sure I cannot add a second picture neither initially nor via edit. Could be my phone. $\endgroup$
    – Bett Struble
    Commented Feb 16, 2019 at 9:28
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    $\begingroup$ Please note that we discourage multiple, disparate questions per post. As is, you are asking about seasons, life, and weather. This makes your question too broad and a prime target for being placed on hold until an edit is made to constrain the request. (Additionally, you might want to understand the difference between weather and climate.) $\endgroup$
    – Frostfyre
    Commented Feb 16, 2019 at 14:27
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    $\begingroup$ A moon that is not largely spherical (I assume you mean spherical when you say "round"; technically, any sufficiently large rotating mass will form an oblate spheroid, possibly with an uneven surface; not a sphere) will very likely have too little mass to have any appreciable impact on tides, regardless of orbital distance. You might want to check out Envite's answer to What's the largest non-spherical astronomical object in the universe? on our sister site Astronomy SE. Also en.wikipedia.org/wiki/List_of_Solar_System_objects_by_size. $\endgroup$
    – user
    Commented Feb 17, 2019 at 12:46

3 Answers 3

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Contributors to minimal seasons:

  • Axial tilt The closer you are to zero, the better (even heating at the equator year-round).

  • Circular orbit The more elliptical your orbit, the more you have seasons (further away from sun for half the year).

  • Orbital inclination When you consider our solar system, you see that Pluto has a non-zero orbital inclination (it doesn't orbit on the same plane as the other planets). You want zero degrees or, lacking that, you need the axial tilt of your planet to match the orbital inclination so that the effect is the same as a zero-degree axial tilt with a zero-degree orbital inclination.

  • Minimal Occlusion You don't want large asteroid fields, gas fields, gas giant planets, etc., between your world and the star. This entry is the least of your troubles as it's a big deal for these kinds of things to get in the way for a long enough and predictable enough period to cause seasons. But, I'm trying to thorough.

  • Stable star A variable star (a star that increases/decreases in brightness) would cause seasons if the variability was predictable and the planet was in the star's habitable zone at both extremes of the variation.

  • Single star You don't want binary or worse star systems. Just one star for minimal seasons.

  • Distant gas giants Gas giants have strong gravity, meaning they can pull water and affect weather on your planet (predictably, causing "seasons") if they're too close. So, you want your gas giants to be well away from your habitable planet.

I think I got everything.

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  • $\begingroup$ This is what I wanted, thank you! $\endgroup$
    – Bett Struble
    Commented Feb 16, 2019 at 20:19
  • $\begingroup$ You can add lack of large scale periodic weather systems like El Niño as well, though they might not be stable ‘seasons’ over geological timescales. $\endgroup$
    – Joe Bloggs
    Commented Feb 16, 2019 at 22:31
  • $\begingroup$ @JoeBloggs, I honestly don't know enough about El Nino/La Nina effects to comment because they may be too dependent on landmass configuration and lunar gravity. Frankly, that would be a very cool question all by itself. "What conditions of orbital and celestial mechanics are necessary to avoid El Nino/La Nina, if possible?" If it isn't possible to avoid them (e.g., they exist due to planetary rotation and chaos theory...), then they might be the only operational season-changing effects the planet I described might have. Very interesting! Thanks! $\endgroup$
    – JBH
    Commented Feb 16, 2019 at 22:52
  • $\begingroup$ @JBH If I remember my climate science lectures correctly it’s a function of the geometry of the oceans and the nature of water: basically raised/lowered sea levels caused by a giant ‘wave’ that slowly bounces up and down the Pacific Ocean. There was more to it than that, I’m sure, but I can only remember the basic gist of the phenomenon. $\endgroup$
    – Joe Bloggs
    Commented Feb 16, 2019 at 23:08
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    $\begingroup$ @JBH Seasons as defined on Earth are almost entirely due to axial tilt. "Seasons" due to eccentricity in the orbit would be uniform over the planet and uneven (long "winters" and short "summers"). Not to be patronizing - you seem to understand most of these factors well. Your answer just read in a way that seemed to attribute seasonal variation (in the Earth sense) to orbital eccentricity, which is a bit misleading. $\endgroup$
    – ben
    Commented Feb 18, 2019 at 1:50
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I’m thinking/hoping/praying that with a small tilt comes nearly no seasonal change, yes?

Yes and no. On Earth, the tilt means that the amount of radiation most regions get from the sun varies a lot (relatively speaking) through the year. I live a few degrees away from latitude 0, and here we only have two seasons: dry and rainy or, as we like to call them, hot and hotter.

You should have a look at The Left Hand of Darkness, by Ursula K. Le Guin. She depicts a world with near zero axial tilt. The whole world is an icy place throughout the year, with all regions experiencing the same season at the same time. However, the planet has a much more eccentric orbit than Earth, so during some part of the year it gets less radiation due to being a lot farther from the sun. The seasons there are cold, colder, and lethally cold.

Another reason to read is the awesome sci-fi in it, but that's beyond scope for the question.

Or... Is the tilt vital to life itself?

Up to you as the author. If life has a start on the planet, it will evolve to adapt to it.

And for that matter, can anybody help me figure out what the weather would be like on a planet with no axial seasons?

Please ask another question just for this and include:

  • Type of star
  • Planet orbital parameters: perihelion (minimum distance from star), eccentricity and tilt (which we know to be zero or close to zero).
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  • $\begingroup$ So what I've gathered is that weather patterns are impacted by uhhhh every aspect of life on earth. 😅 Great. We'll I guess I'll just make it up as I go, try to match weather with climate and give the planet wet and dry "seasons" according to their minimal tilt. Thanks $\endgroup$
    – Bett Struble
    Commented Feb 16, 2019 at 20:23
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minimal seasons[...] right?

Right.

mild weather right?

Depends how you define "mild". Subpolar regions would not have any short summer and would be permanently frozen. There would be no savanna with rainy season, as there would be quite narrow band between tropical rain forest and deserts with effectively no rain. On the other hand in temperate regions you'd have nice growing season for whole year.

Actually such high temperature gradients may lead to slightly more violent winds.

I personally would think about rearranging the climate zones on those map, as they look a bit odd (like desert island in SE, which for me should be rather in some temperate zone).

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  • $\begingroup$ Actually that’s perfect because as you can see, I’ve created deserts and jungles extremely close, all things considered. Yes you’re right, Ekraxi (the bottom right SE giant island) would be more temperate and indeed used to be, but it was essentially burnt to a sizzling crisp ages ago in a very violent war involving people who can move and summon fire vs people who can move and summon wind. The conflict concluded in explosion and the barely-subterranean-heat has taken thousands of years to cool enough for most greens to grow again. That’s why it’s so charred 🙂🙃 $\endgroup$
    – Bett Struble
    Commented Feb 17, 2019 at 22:13
  • $\begingroup$ Oh— and the other southeastern Island, Chipalulu, is actually pretty chilly, it’s just also fairly desolate. Don’t forget, cold deserts exist too! $\endgroup$
    – Bett Struble
    Commented Feb 17, 2019 at 22:16

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