# Can a planet with only one pole cap exist?

I am imagining a planet more or less earth like. I would like it to have only one pole cap, so only the southern hemisphere has a snow-covered continent. The trick is, I don't want it to lie completely on its rotational axis because that would cause the days be as long as seasons (please correct me if I'm wrong). Days should actually be more or less like the ones on Earth.

Would there be some geological phenomena that would prevent an ice cap from forming? A warm current maybe? Or something in the atmosphere? Thank you!

• Technically, earth only has one "snow-covered continent" at a pole, as the north pole is in the Arctic Ocean. – Seeds Jul 5 '16 at 20:07
• @Seeds could you expand on that? I'm not an expert, to me the Arctic and the Antarctic both count as continents – L.R. Jul 5 '16 at 20:13
• @Seeds Oh I see what you mean, sorry. But the point is, there is snow in the arctic. I don't want it there. – L.R. Jul 5 '16 at 20:15
• England has a much milder climate than it would otherwise have at it's latitude due to an ocean current, but to properly answer your question more detail would need to be forthcoming as to what you want. The heat has to come from someplace. – Seeds Jul 5 '16 at 20:22
• Not sure if this is possible, but perhaps a binary star system, where one star is much much dimmer and fartger than the other. The ice cap sees the dim star once a day, but it doesn't recieve enough energy to melt the ice – Ovi Jul 5 '16 at 20:34

A polar ocean that extends far enough from poles for significant parts of it to be ice free year around will not form a polar cap. Since water is densest few degrees centigrade and sea water freezes few degrees below zero, water circulation will push free floating ice away from the poles unless the currents are blocked by land masses as they are in the Arctic. Ice simply can't get away from the Arctic.

Note that in this scenario you will have zones where cold currents coming away from the poles collide and mix with warm currents flowing towards the poles. The average water temperature there should be around the densest point and the water will sink. This kind of robust water circulation would probably make the waters fairly nutrient rich and fertile. Not sure of the effects on climate, but the mixing zone would have fog, I think?

### Cover the icy pole with a continent, and the other pole with open ocean. Make the planet about $20^\circ C$ warmer than the Earth.

Oceans are great temperature distributors, bringing relatively warm water to what would otherwise be far colder climates. Because of this, a pole with an ocean on it is going to be significantly warmer than a pole covered by a land mass. On Earth, the North Pole fluctuates between $20^\circ C$ ($36^\circ F$) and $30^\circ C$ ($54^\circ F$) warmer than the South Pole, depending on the time of year, with the difference most pronounced in the Summer.

On an Earth-like planet which was around $20^\circ C$ ($36^\circ F$) warmer, the south pole would remain below freezing year round, retaining an ice cap, while the ice cap covering the North Pole would rise significantly above freezing and melt during the summer. Ice caps have a much higher albedo than open ocean, which is good at absorbing heat, so it's likely that without a summer ice cap, the difference in polar temperatures would be even greater than what we see on Earth.

Wider ocean channels between the equatorial oceans and your polar sea would also increase polar temperatures, On Earth, the Arctic Ocean is largely ringed by land, which helps the ocean stay cold by limiting the degree to which it exchanges water with warmer oceans. Arctic regions on Earth which are more open to currents from the south have less ice than those which are more landlocked, with open ocean stretching as far north as Svalbard, even in the winter, while the Northern cost of Alaska remains ice bound year round, despite being significantly further south. The further warm ocean currents from the south are able to penetrate your polar ocean, the more difficult it will be for that ocean to form a cap of sea ice.

• Hope you don't mind the edit, I personally found it helpful. – Xandar The Zenon Jul 6 '16 at 2:08
• Helpful, perhaps, but you don't need to add 32 for differences in temperature. – ckersch Jul 6 '16 at 3:27
• 20 degrees C is 68 degrees F, is it not? Because 32 degrees F its just a step up from freezing. Otherwise something is definitely wrong. I think your math might be a little bit off. – Xandar The Zenon Jul 6 '16 at 3:33
• If this was Earth, just imagine all the northern continents moved south to open up the Arctic region and an icecap won't form. This was the case when the northern landmasses were further South than they are now. Once they closed in, the North Pole had an icecap. Just keep the northern landmasses in the South, and you have an ice-free pole. – a4android Jul 6 '16 at 6:27
• A delta of 20 degrees C equals a delta of 36 degrees F. Note "was around 20∘C warmer". – Apollys Jul 17 '18 at 20:02

There are several ways I can think of, and most involve volcanism:

1. Have a pole sea with under water geyser strings along the bottom. As long as currents rotate the heat without too big a run-off, no ice should build up. It also helps if the sea becomes extra-salty and/or has more mineral content that Earth oceans have.

2. Immerse one pole with eternal clouds from active volcanoes. The heat will remain captured under the clouds. Don't make em too high though!

3. Have a giant pole desert. So little water is present that evaporation outruns any snow build-up. But beware bigger temperature extremes this attracts, where more than water freezes. You'd need something far bigger and more elevated than Antarctica, with circular winds outside the frozen zone thrown in as well.

• Not sure 3 works since Antarctica is a desert. – Bellerophon Jul 5 '16 at 20:54
• A much bigger, dryer desert than Antarctica. Antarctica has frozen sea at the edges. – Bookeater Jul 5 '16 at 20:58
• Antarctica is the biggest desert on earth so a larger desert would likely have to have extremely odd wind currents to exist. It is probably just possible but 1 and 2 are more plausible. – Bellerophon Jul 5 '16 at 21:02
• Antarctica gets winds directly from over sea. You'd need such a size that only very dry air reaches the frozen zone. Probably circular winds around the frozen zone are needed as well. And indeed this option is positioned last. – Bookeater Jul 6 '16 at 4:27

I think you can do this, at least for a few thousand years at a time. Take a planet that's generically earth-like, but has a significantly more eccentric orbit.

If you only want a north polar cap, arrange that southern summer happens during the period when the planet is near its aphelion; there's continual daylight at the south pole, so any ice that was there would melt. Southern winter then happens around the time of perihelion. There's continual night at the south pole, but if you get the combination of axial tilt and eccentricity right, the whole planet is warm enough that a southern polar cap doesn't form. This may mean that the northern polar cap only exists during northern winter.

This state of affairs won't last for many centuries: the planet's axis will undergo precession and will gradually cycle between the state you want and the opposite, when there's only be a south polar cap; in between these states you'll have both polar caps.

You could have more salt, and some other substance in the seawater that lowers the freezing point of water. Say that your seawater becomes ice at -150C (-238F), instead of -2C (28.4F) as on Earth.

Now all you need is for one of the poles to be on land instead of on water. The pole with land will have ice on it. The pole with an ocean on it will never freeze.

• Good in theory but lowering the freezing point low enough would probably lead to gaseous seas at about 20-30 Celsius so the planet would be very dry. – Bellerophon Jul 5 '16 at 21:15
• @Bellerephon I'm curious. How does that work? – Renan Jul 5 '16 at 23:07
• Well most elements with a freezing point of -150C boil below 0C so the sea would be gaseous at normal temperatures. – Bellerophon Jul 6 '16 at 15:18