A Planet with a warm south/cold north - how?

[Enjay]

OK, a bit of a weird one here but maybe someone will have an idea. This is, initially at least, for a role-playing scenario.

I'm trying to come up with some astronomical configuration that would allow a planet to be much warmer in the southern hemisphere than the north. South pole about 60°C (140°F) and the north averaging around -20°C (-4°F).

The planet needs to be more-or-less Earth-like otherwise. So areas between these extremes are relatively habitable by Earth-like creatures.

My initial thinking was to have the planet tilted much like the Earth is (Earth's tilt is about 23 degrees). However, as Earth orbits the sun which pole is pointed towards the sun changes during the orbit. Tomorrow being the vernal equinox means that our tilt is currently "side-on" to the sun. So, my idea was to have the planet always have its south pole angled towards the sun (so permanent summer in the south) and the north away from it (permanent winter).

However, I guess this would have two obvious problems. Firstly, I think the gyroscopic-like(?) forces of the rotating planet might prevent the tilt angle working like that. Secondly, that fact that such an arrangement would do what I want it to, would also cause a problem: no seasons at all, and I want there to be at least some seasonal variation on the planet.

So, can anyone think of a planetary configuration that would allow the climate in the south to always be hotter and sunnier than the conditions in the north (with more habitable, seasonal areas between the extremes) and which would work with physics?

Nothing is off the table - second suns etc are all fine if a configuration that works can be arrived at but I can't think of something that would do what I want but which would still agree with the laws of physics (as I understand them - I'm not a physicist). Maybe it just can't happen?

[Kzer-Za]

If you want one of the poles to be warmer than the equator, then I think it's not possible. If you just want one of the poles to be significantly warmer than another (being still somewhat colder than the equator), it may be possible with sufficient volcanic activity. Though this much activity would probably make the area very subjected to earthquakes. Also I suppose it would make the weather there very rainy and foggy.

[Rachael]

The Earth already does this, it's just way less obvious now since we're at the dip of the Milankovich cycle. But the reason for our ice ages is that we actually have an elliptical orbit which is influenced very heavily by other (more slower moving) planetary bodies. When our solar system has the planets reasonably spread out our orbit becomes more balanced and circular, and the planet heats up (as it currently is doing). We're actually in a very hot stage for the planet at the moment and on the decline (another harrowing sign of climate change, since we should be starting to get colder), but when the planets start to align again our orbit will shift to become more elliptical and then during this time, we'll be in an ice age, where half of the year only one hemisphere is close to the sun, and during the other half of the year the entire planet is away from the sun. This is one of the causes for the permafrost to form on the ground during an ice age. Another factor could also be cosmic dust which during one half of the year can also help to obscure the sunlight.

As for how you would work that into a fictional setting - that is not something I can really help you with, except to give something that is based in reality as a starting point.

Here's some more information for you:
https://climate.nasa.gov/news/2948/mila ... s-climate/

And an entertaining video to go along with it:

[Kaution]

The easiest way to plausibly achive this, without even any astronomical shenanigans, is to have the colder part of the planet to be very mountainous and thus at a higher altitude then the warmer part of the planet.

The tinner atmospere would cool that part of the planet down.

https://www.sciencefocus.com/planet-ear ... o-the-sun/

[Scripten]

In addition to what's been said already, there are a few ways to go about this. Your best bet, like Rachael said, is probably a more elliptical orbit that lines up with the changes to the axial tilt of the planet. That is, when the planet is at its closest points to its sun, the south pole is heavily tilted toward the sun, and when the planet is further away, the tilt is aligned slightly to the north. It's also true that planets needn't be perfectly aligned to their star's elliptical, so that tilt could very well be off-center, such that the south is biased heavily.

This link has a ton of good info on why the Earth's rotation, tilt, and motion work the way they do, and the consequences to our climate. Take a look at Axial Precession specifically, which is roughly 60% down the page:
https://climate.nasa.gov/news/2948/mila ... from%20now.

Finally, if you really wanted to bias the south, you could tidally lock the planet to its sun and set the rotation to be closer to 90°. One of the (many) consequences of this is that days in the south would be significantly longer than the north, and seasonal variation would be, to put it mildly, rather extreme. This might've been what GRRM did to the planet in Game of Thrones, such that winters are a decade long, though I'm not sure. Checking out info on Uranus, despite it being a gas giant, might help if you want to base the details on its irregularity.
https://solarsystem.nasa.gov/planets/uranus/in-depth/

[Gez]

The simplest way to have temperature differentials is, of course, "a wizard did it", but the next simplest explanation is "jet stream".

Here's an example from the real world:

We tend to underestimate how much to the South America is compared to Europe. the fact that Venice in Italy and Montereal in Canada have about the same latitude (45°26' vs. 45°30') is not really an intuitive fact.

Altitude plays a role, so a high plateau will be colder, all else being equal.

The ground is important too. An arid rocky place will retain much more heat year-round than a wet grassy place. Different materials have different heat absorption and restitution properties, albedo plays a role as well -- a white ground will reflect sunlight and its associated heat away, while a black ground will absorb it, living groundcover will try to regulate its own heat, and flowing water has a cooling effect (mostly through evaporation, but also in part because the water is flowing from somewhere higher where it's cooler).

[Gez]

With that said, a South Pole temperature of 60° with a north hemisphere average temperature of -20° is kind of extreme.

I'd suggest perhaps having a binary star system, with the planet orbiting Star A, while the orbital period of Star B around Star AB's common center of gravity is long enough that it lasts several millennia. If the orbital plane of Planet is about perpendicular to the orbital plane of the stars, that would allow Star B to remain in Planet's southern sky for thousands of years.

We kind of have stuff like that in some system, most spectacularly in Castor where Castor C has an about 14000 year orbital period around Castor AB. (The fun thing being that Castor A, Castor B, and Castor C are all binary stars. It's neat.)

[Enjay]

Oh wow! Some excellent thoughts and suggestions here. I'm going to have to go away and digest them and see what works for me. I had considered a binary star before but my understanding of how that might work was too limited and... well, just plain wrong.

Thanks again - and further thoughts are welcome.

[axredneck]

Google for "eyeball planet"

[Enjay]

Having dug into it as far as I feel I want to, it looks like exactly what I was originally hoping to achieve isn't really something that would be likely occur in nature (or at all). However, a combination of the suggestions made on here has allowed me to come up with a rationale that allows me to create a world with suitable climatic zones even if some of it does fudge things at the edges by using jet streams and macro weather system etc. that I have no real evidence for actually occurring in the geography of the world (other than it feels right enough not to feel overtly wrong). I have managed to stop short of "a mage did it" though.

Given that this is all just background to the world and isn't strictly required to be 100% on the nose anyway, what I have now is certainly good enough.

Thanks.