Desert poles but arctic equators; trying to find out if specific way is possible

Question

I'm trying to create a planet with a hot desert north and south pole but a cold equator. Is this possible? and if so how? And if it's heavily related to space how would night and day work on this place?

I don't want a high fantasy reason, the world having 2 suns, or a network of underground volcanoes that are only heating up the north and south but not the middle.

Answer 1

Have an axis tilt [1] over 56° or under 124°

Between these points the poles and the equator switch climate. Technically speaking the poles simply have a higher thermal insolation average per year than the equator. This graphic [5] shows the relationship between axial tilt (obliquity) and the yearly average temperature (insolation) for a given latitude.

Looking at the graphs having an axial tilt near the limits won't give you polar deserts (actually the poles would be tropical with a ring of deserts around them, but some tweaking could reduce the rainforest to desert) and equatorial ice capes, but overall global moderate average temperatures. At 90° axial tilt, the poles have the warmest average temperature and the equator the coldest.

Yet keep in mind that I'm talking about yearly averages. An object that is at absolute zero for half a year and at 273 C° for the other averages out to moderate 0 C°. At 90° this illustration isn't far from the fact. If one hemisphere on a 90° world experiences winter it also experiences night. The "night" lasts for 1/4 of the year. Vice versa for the other hemisphere and summer. Autumn and spring will be moderate-ish.

The equator will be the coldest place on such a planet, but as the graph shows not nearly as cold as Earth's poles. I'm uncertain if permanent icecaps are possible and while they aren't out of the question a tundra belt seems more plausible in most cases. The seasons in the region will be two "twilight" seasons in winter and summer and "rotation day" seasons in autumn and spring.

The poles will be deserts in the sense of desolate wastelands, swinging between the hottest and coldest points on the planet on a half-yearly basis. The intermediate seasons will be slightly more moderate, but the temperature difference will purge anything staying longer than these seasons.

How extreme the temperature differences will depend on whether or not the circulation cells in the atmosphere and the rotational forces creating them are stronger than the winds thermal pressures, which will try to redistribute warm air equally across the surface. This is what happens on tidally locked planets where similar temperature differences can be found according to the latest simulations. I wasn't able to find any material on this case so choose whatever fits your needs.

Conclusion

Changing axial tilt is by far the easiest way to achieve your goal. My recommendation would be to place the planet near the outer edge if the habitable zone to make the equator as cold as possible, raising the plausibility of an ice shield surviving the intermediate seasons. The poles will still be deserts going from frying to freezing, but that's a cool extra. Axial tilt wise I would stick close to 90°, keeping the equator as cold as possible and making the seasonal cycle simple. While nothing short of a climate simulation will give you the full picture, this video [2] might help.

For further reading, I would recommend this paper [3] on versions of Earth with different axial tilt.

[1] https://en.m.wikipedia.org/wiki/Axial_tilt

[2] https://youtu.be/J4K3H9aNLpE

[3] https://www.youtube.com/redirect?event=video_description&html_redirect=1&redir_token=3JAkHxRedLFbHxzvUdN1gVlo-1p8MTU1NjYxOTY0MUAxNTU2NTMzMjQx&q=http%3A%2F%2Fgoo.gl%2FQGA6Ga&v=J4K3H9aNLpE (Pdf)

[5] https://m.imgur.com/yJHPwd7

Answer 2

Starting with the Earth as a template:

• Move it closer to the sun
• Reduce axial tilt
• Add thick rings

Rings around a planet like Earth would last a few million years at best, but we've been around for less time than that.

The poles would be hot due to star proximity. The rings would reduce radiation on and close to the equator, making it cold.

Answer 3

Some expansion on this comment:

Slap a thick enough atmosphere on your planet (earth + 25% at least) and create Tibetian-like highlands all around your equator, while eliminating axial tilt to create moderate climate. Plus, huge continents around the poles with next to no precipitation.

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1. Remove axial tilt - Why? Because this removes most of the seasonal changes, especially the long polar nights during winters, thus increasing the average temperature at the poles at least a bit. This should counter the effect of low solar irradiance a bit and prevent the forming of ice caps.
2. Add huge continents at the poles - Why? The interior of continents tends to have a harsher, drier climate, aka continental climate. Take a look at the Gobi desert. Dry, sometimes hot, sometimes freezing - located at the heart of the Asian contintent. Antarctica is another example. - You will get Gobi-like deserts, but not Sahara-like. Dry and inhospitable, but not scorching hot throughout the year.
3. Tibetian highlands - Why? The Himalaya and Tibet directly to its north are about the same latitude as Cairo or Florida. Though not directly polar, the great altitude creates polarlike conditions with permafrost, glaciers and lots of snow. For good measure, add another 1000 m of height, as to why: see below. Also huge mountains make good places for lush hidden valleys full of wise men, mystical artifacts and/or fountains of youth.
4. Make the atmosphere thicker/higher - and warmer - Why? The atmosphere needs to be a bit warmer than our Earth's, in order to prevent the poles from freezing all year round. About 5°C should do the trick, maybe less. Hard to answer without a climate model. When you make the planet warmer, your highlands need to be higher up in order to have the desired climate, and in order to be still hospitable/traversable you need more atmosphere. Add about 2 km in thickness for good measure.

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So,this should get you the sketched conditions.

You will not have real ice caps at the equator, stretching over hundreds of miles, but rather huge mountains, peaking through glaciers which flow around them and bury the highlands to some extent.

You will not have Sahara-like, scorching hot deserts at the poles. This is not really possible. Still, temperatures could change by 30 to 40°C during one day, and it will be really dry.

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Possible problems your world could encounter:

• You put a giant ring of rock in the equator. This might mess up the climate. The flanks of said ring should be lush jungles, since winds from the north and south will push moist air up the flanks. Just like in northern India. Exchange of air across the euqator is limited, which could prove a problem - or a story-element (think jet-like winds rushing through the few passes leading across the Wall).
• You put huge continents at the poles. This will mess up your climate. Also your ocean currents are hellish, if you stick to circular oceans. Same would go for wind currents (take a look at the Screaming Sixties) engulfing Antarctica.
• If you don't leave enough room for oceans, your world would be about as dry as the planet Dune. If you limit your continents to the described three, travel between them would be rather scarce.

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Okay, I tried to make it as short as possible and to not get lost in detail. Still, I feel I could expand on some issues, don't hesitate to ask.

Answer 4

If you don't insist that your polar desert be hot, look no further than Earth.

The South Polar Plateau in Antarctica is one of the most arid landmasses on Earth, with annual precipitation of about 7 cm of snow (convert that to liquid, and that's drier than the Atacama Desert in Chile and Peru). The northern ice cap is similarly arid, though it's harder to notice with the sea ice (formed by surface freezing of sea water, for the most part).

Move the Earth a couple million miles further from the sun, and the poles will get even drier (less water evaporating from the oceans).

Answer 5

Physics is not your friend here, the equator gets more sunlight coming in at a more vertical angle and passing through less atmosphere. This means higher temperatures.

The one thing that does counteract that is altitude, so the solution to your problem is to have a very high plateau or mountain range that happens to run roughly around the equator of the planet. Just think of the Himalayas for example which are at the same latitude as Egypt and India and yet have permanent snow cover.

It would be an odd coincidence to have it run like that and continental drift over millions or billions of years would change things but for several million years you could have a mostly cold equator with maybe occasional warmer valleys where the altitude drops and obviously if you had any coasts or oceans they would be tropical.

Answer 6

Step 1: Move your planet further from the local star. This reduces the temperature, and freezes the equator

Step 2: Situate large volcanos, geysers and similar geological activity at the North and South poles. These provides heat for your deserts

Answer 7

While it is improbable that a planet like this would exist given that we have not yet observed one in our universe. Having the planet's axis of rotation be a line tangent to it's orbital path would move your equator to be a band that would run through where the poles are on Earth while the new poles would be on the right and left sides of the planet.

Answer 8

It is possible that the correct design for a habitable Earth-sized exomoon orbiting a gas giant planet in the habitable zone of their star might help with making this possible.

You should look up previous questions and answers about possibly habitable exomoons of gas giant planets.

One thing which they say is that for the orbit of a moon around its planet to be stable long term the orbit of the planet around its star has to last at least nine times as long as the orbit of the moon around its planet. So if the orbit of the moon around its planet lasts 10 Earth days, the orbit of the planet around its star would have to be at least 90 Earth days long.

And if the planet's orbit around the star is not much more than nine times as long as the moon's orbit around the planet, the combination of them might keep parts of the moon in sunlight or in the shadow of the planet for longer periods of time and thus cause those parts of the moon to heat up or cool down more.

Remember that the earth sized moon will be tidally locked so that it will rotate with the same period as it orbits around the planet. Thus there will be a planetward side of the habitable moon that will always face the planet, and an antiplanetward side of the moon that will always face away from the planet.

The shape of the shadow of the planet will depend on the values of the diameter of the star, the diameter of the planet, and distance between the star and the planet.The umbra, the totally dark part of the shadow, should be a cone that gets thinner and thinner with distance from the planet and comes to a point, while the penumbra, the partially dark part of the shadow, should be a cone that spreads out with distance from the planet, and extends out into space forever.

When the moon is in the penumbra the reduced light from the star may be enough to make water in the colder parts of the moon, such as in a hypothetical high equatorial ridge around the moon, freeze. And possibly if the sizeof the umbra at the distance of the moon is just right, only the equatorial ridge regions will ever been in total darkness and get even colder whenever the moon enters the umbra.

You might try modelling two different designs of the star/planet/moon system to see which gives the hottest poles and the coldest equator.

In both models the moon will orbit around the equator of the gas giant planet and the moon's own equatorial plane will be in the same plane as it orbits the gas giant planet, because tidal interactions between the moon and the planet will alter the moon's orbit and rotation into that configuration billions of years before the moon has a breathable atmosphere or advanced multi celled lifeforms such a intelligent beings evolve on that moon.

In one model the orbit of the moon around the gas giant planet should be in the same plane as the orbit of the gas giant planet around the star.

In the other model the orbit of the moon around the gas giant planet should be in a very different plane - titled about 90 degrees, similar to the axial tilt of Uranus - from the orbit of the gas giant planet around the star.

My answer here Polar Heat, Equatorial Cold - Climatic Effects of Inverted Global Temperatures1 discusses how the second model would affect the climate and possibly result in cold equator and hot poles.

There have been many questions about possible Earth sized habitable moons of gas giant planets.

I have answered a number of those questions.

Here is a link to a previous question and my answer to that question includes a link to a question and answer which has links to previous questions and answers.

What are the day and night fluctuations for a moon orbiting a planet the size of Jupiter?2

The article "Exomoon Habitability Constrained by Illumination and Tidal heating" by Rene Heller and Roy Barnes Astrobiology, January 2013, discusses factors affecting the habitability of exomoons.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/3

Also see my answer here:

How long will it take to discover they live on a moon and not on a planet?4