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The basic concept of this planet is that, the planet has a tilted axis (you probably guessed that already) which results in the South Pole constantly facing towards the sun. This would result in the planet having a 'bi-polar' like climate, with everything from the North Pole down to the equator being a cold and frozen environment, getting warmer as you go south towards the equator, while everything South of the equator getting even warmer and warmer with the South Pole (if it is a present landmass) being absolutely scorching desert.

I'd imagine that the equator, being the halfway mark being hot-land and cold-place being somewhat humid and full of rainforest/jungles and plains. Though that is from my basic understanding of climates and planet related science. Mountains, rivers and so on would also above an influence on the terrain of the world. Wow an important distinction to make is that this planet isn't tidally locked, just it has a very wonky axis. So how plausible is such a thing, a little too outlandish or something entirely possible?

user
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Sgtwolf00
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    The tilted axis part is OK. See the planet Uranus for precisely this. However, as the planet orbits its star the face pointing at the "Sun" will change progressively over its "year". At the half year mark hot-land will be cold-place & vice-versa. A change of seasons on steroids. Also, in hot-land it will be day and cold-place will be night. see @LoganRKearsley's answer for more details. – a4android Aug 04 '17 at 06:09
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    I am having a hard time understanding your contradictory requirements. If the south pole always faces the sun, why not have it tidally locked? What would rotation bring into effect that you couldn't get by having a tidally locked planet? – Jason Goemaat Aug 04 '17 at 11:17
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    BTW, a planet like this would be almost exactly like a tidally locked planet, the rotation provides rotating stars, but not much else. – ths Aug 04 '17 at 12:06
  • @Jason Goemaat, a tidally-locked body (like our moon) doesn't rotate on its own. This means the view of stars on the night side only changes due to orbit. A rotating planet would also change stars daily. – JBH Aug 04 '17 at 15:19
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    There is at least one definitional issue with your question. "Tilted axis" by definition cannot "constantly [face] towards the sun." – Kevin Aug 04 '17 at 17:49
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    @JBH: A tidally-locked planet or moon does rotate, it's just that the rotation period is the same as the orbital period. If for instance the Moon didn't rotate once a month, here on Earth we'd see the entire surface in that period. – jamesqf Aug 04 '17 at 18:08
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    @jamesqf, :-) that's technically true, but explanitively irrelevant. We all know a tidally-locked object has one hemisphere permanently facing the gravitational master. The OP's question is looking for rotation independent of the "lock". The moon has no rotation independent of the "lock." – JBH Aug 04 '17 at 18:18
  • @Kevin, The point of the OP's question was to investigate the "definitional issue." Please see Logan R. Kearsley's quality answer, which helps the OP understand the nature of the "definitional issue." – JBH Aug 04 '17 at 18:22

  • Life like humans won't be able to survive on a tilt greater than 80 degrees. So to answer your question as close to 80 as your comfortable and it will still be plausible. Final thing to note is that if you go above 53 degrees your temperature zones reverse, so your polar regions will be at the equator and your tropics will be be at the poles. – Choosing axial tilt for human habitable planet for largest temperature variations

     – Mazura Aug 04 '17 at 18:26
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    @ths The stars still rotate on a tidally locked planet. – Spencer Aug 05 '17 at 13:16
  • @Kevin: somewhat pedantically, you can be tidally locked without having a tilted axis, and you can have a tilted axis without being tidally locked. One does not automatically equate to the other, although there is some overlap as to the effects that you experience because of them. There's nothing preventing OP's south-pole-tidally-locked planet to also rotate around its north/south axis. – Flater Aug 05 '17 at 14:04
  • @Spencer sure, but only one per year. – ths Aug 05 '17 at 15:18
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    @Flater "There's nothing preventing OP's south-pole-tidally-locked planet to also rotate around its north/south axis." On the contrary, yes there is: angular momentum. Angular momentum can be overcome, but the answers discuss the consequences of doing so. – David K Aug 05 '17 at 21:55
  • @DavidK: Tidally locked (1 - rotation of up/down axis of solar plane) and planet rotation (2 - rotation on N/S axis) are two separate rotations. If I'm reading Euler's rotation theorem correctly, then a set of two rotations can always be expressed as a single rotation. So if the planet is given a specific rotation vector (which just happens to be equal to the outcome of combining 1 and 2), then it is possible for this system to exist and maintain itself. Highly unlikely, improbable, but not impossible. – Flater Aug 06 '17 at 08:34
  • @DavidK: Maybe I jumped a step here. It's perfectly possible (but again unlikely) for a planet to experience no rotation whatsoever. It moves around the sun without any rotation (functionally, 1 solar day = 1 year). Now imagine a force acting on the planet (e.g. comet grazing the planet) which gives the planet that exact rotation that I described (which is equal to to combination of rotations 1+2). I see no reason why that physically cannot work. – Flater Aug 06 '17 at 08:40
  • @Flater Starting the motion is not an issue. Maintaining the motion the bone of contention. Do you know how a torque affects an angular moment of inertia? There are (or were) toy gyroscopes that a child could make to rotate in the desired way, but you had to keep the axis of the gyroscope horizontal and rest one end on a support. The torque from the gyroscope's own weight would cause its axis of rotation to precess in a flat circle. So if there are massive forces tending to push the planet's axis out of the plane of revolution, it can be done. Where do those forces come from? – David K Aug 06 '17 at 13:07
  • @Flater By the way, you read Euler's rotation theorem incorrectly. It refers to two finite rotations of an object, i.e. you turn it through an angle $\theta_1$ about one axis, stop turning it, then turn it through an angle $\theta_2$ about another axis and stop turning it. – David K Aug 06 '17 at 13:58

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Utterly impossible.

You simply cannot have one pole of a rotating planet always oriented the same way towards the sun, for the simple reason that the pole always points in the same direction in space, but the planet moves around the sun. Keeping one pole always pointed at the sun despite the planet moving from one side to the other over the course of its orbit would require continuously applying gigantic torques--enough to completely reverse the planet's spin twice every orbit--for which no physical mechanism exists, and which would tear the planet apart if you magically willed them into existence.

A synchronously rotating (tidally locked) world would give you most of the same effects, but since you explicitly ruled that out... sorry, it just can't happen.

Logan R. Kearsley
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    Conservation of angular momentum, in other words. – bcdan Aug 04 '17 at 03:08
  • Would the magnatude of the energy needed to provided that amount of torque be comparable to the solar energy received from the star? Otherwise one could conceivably have some kind of "solar axle" energy converter taking up a large part of the south pole to continually stabilise the planet (assuming sufficient technology and a reason to do so). – 8DX Aug 04 '17 at 12:57
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    @8DX: I guess thats impossible. To get an idea how much energy we are talking about I quickly made some calculations (So I might have done some mistakes): The energy required for earth immediately getting velocity to escape sun would be 1,13032495×10³⁶ Joules. Just stopping its spin would already take 2,9×10²⁹ joules(Thats not even that far from earths escape energy). For reference, the lifetime energy output of our sun (assuming it will live for 10billion years overall) is only 1,3×10⁴⁵ Joules. So good luck draining that much energy from sun. – Zaibis Aug 04 '17 at 13:22
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    What about precession, earth has a precession cycle of about 26000 years, if the orbit were also 26000 thousand years wouldn't this work? OK, the torque from the sun would be much different when orbiting at a great distance, but could there be a combination of extreme orbital conditions that result in polar locking – Gary Walker Aug 04 '17 at 13:34
  • @GaryWalker Even if we assume there is some source for torque to produce that precession in a 26000-year orbit, that's more than 17 times farther from the sun than Pluto at aphelion (877.6 AU). That might still be bound to the sun... but the Earth would be a frozen ball of nitrogen ice. And Earth isn't tilted that much; as a result, the Earth's precession doesn't have to come anywhere near completely reversing the Earth's spin, even over 26000 years. – Logan R. Kearsley Aug 04 '17 at 15:40
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    @LoganR.Kearsley I was thinking earth could be orbiting a gas giant to supply more torque and heat. Just trying to think outside the box to salvage a very unusual set of orbital parameters. – Gary Walker Aug 04 '17 at 16:13
  • @GaryWalker In that case, it would just become locked to the gas giant instead of the star, and then you have a much bigger problem- you don't merely have to change the rotation axis of the planet, you also have to provide enough additional external torque to alter its axis of revolution around the gas giant, which is a much larger store of angular momentum! – Logan R. Kearsley Aug 04 '17 at 16:28
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    For reference the torque required for an earth-like planet to do this is about 1.4 * 10^27 N m, which is about 70000 times the magnitude of the torque that causes the precession of earth's Equinoxes. – Kyle Aug 04 '17 at 16:32
  • Can a planet not have two axes of rotation, one orthogonal to the orbital plane and the other within it? – Tim Sparkles Aug 05 '17 at 00:09
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    @Timbo Not in three dimensional space. In 4 dimensions and higher, it can, but we do not live in such a universe. And even if we did, neither axis, if not perpendicular to the plane of the orbit, would remain in the same relative orientation to a star while the planet orbits around it. – Logan R. Kearsley Aug 05 '17 at 00:17
  • @Kyle what formula did you use to calculate that? – Spencer Aug 05 '17 at 16:17
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    @Spencer I calculated the angular momentum of Earth, then calculated the total integrated change of that angular momentum over a year (2 * pi * P, because the angular momentum vector makes one rotation in a year) and then divided by one year. That gives the average torque. Likewise for Earth's precession (only that one's multiplied by the sin of the precession angle and has a period of 26000 years). – Kyle Aug 05 '17 at 19:34
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    @Zaibis the numbers you've provided are not close at all to each other. Saying the rotational energy is close to the energy required for the Earth to reach escape velocity is about the same as saying the energy of the nuclear bomb dropped on Hiroshima (6.3×10^13 J) is close to the energy contained by a candy bar (1.2×10^6 J). What's it's actually somewhat close to is the daily energy output of the sun (3.3×10^31 J). (My numbers came from https://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)) – Rob Watts Aug 05 '17 at 20:55
  • @RobWatts: Well "close" is a matter of perspective. And released energy vs contained energy vs required energy is a whole different thing. While My point in saying they are kinda close came from 8DX question to collect the energy from the sun. My first point was the energy to switch the spin is "only" 7 orders of magnitude different from kicking of earth of suns orbit. Thats twice a day ~13.000 years collected energy to make earth just lift of from sun like a space rocket. Felt fair enough for me to call it "close". And even the 9 orders of magnitude from the "Spacerocket earth"'s launch to... – Zaibis Aug 07 '17 at 09:01
  • ...the overall lifetime energy output of the sun, is considerable to be close for me, if I just consider, that turning earths spin 2 times a day 365 days a year over 6 billion years ends up on a requirement of 1,27x10^42 joules. Thats 3 orders of magnitude in difference. So for this to happen it had to be 0,1% of suns overall energy output from its very first day. So I felt it was appropriate to relate the numbers. While I don't think there is a meaning full way of building a nuke out of 10.000.000 candy bars, which feels like a provocation shot in the void. – Zaibis Aug 07 '17 at 09:04
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@Logan R. Kearsley is correct and you should accept his answer (I upvoted it), but for the sake of your continued exploration of your world, remember that Uranus has the axial tilt you're describing, it's simply not polar-locked to the sun. For an introduction to its seasons, check this out.

JBH
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    I disagree; this sounds like an answer to me. Granted, not a great answer (it could go in much more depth, as well as be rephrased to more explicitly stand on its own) but still an answer, as it points to a real-world example resembling what the OP wants and discusses the ways in which that real-world example is similar to and different from what the OP wants. – user Aug 04 '17 at 07:07
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It might be possible. But you have to think outside a few boxes.

For one thing. What makes a sun your sun? Do you have to orbit it?

We already do exactly this with Polaris. We just don't think of Polaris as our sun.

Polaris doesn't exactly keep us warm. But why shouldn't it? Because it's fairly long way away. Any way to fix that?

enter image description here

Sure, make it a black hole that spews x-rays along it's axis. The charged particles circling down to their deaths emit radiation in a highly directional way.

Quasar's will do the same thing for you. Just well. BIG. Whether these are really different names for the same thing is a debate I'd rather not get into.

Precession is something to understand whenever you're dealing with an axis. Yes overtime we drift away from directly facing Polaris like a spinning top. But that's a mere wiggle in your temperate zone compared to what happens if your quasar decides to do the same thing and be a pulsar. This would mean every so often your sun just turns off.

Is this stable? Not sure. Does this even have a Goldilocks zone that can support life? Not sure. But if you just have to be this weird I think this is the most plausible. Pack your sun screen.

candied_orange
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    That might just be weird enough to work, Polaris isn't stable in our sky over geological time but it could be if our axis didn't shift. I'd use a Quasar, it can be a lot further away for a given intensity of received radiation so will be more stable both in position and the gravitational equation, since a world in this situation is going down the hole eventually. – Ash Aug 04 '17 at 17:05
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Basically, you are asking about a planet that has, 1) a 90 degree tilt, and 2) a precession period equal to its orbit period (ie, that takes exactly one year to make a full precession).

I have asked the general question - concerning just the item 2) above, irrespective of 1), here: Can there be a planet for which orbit and precession take the same time?.

The discussion seems to demonstrate that it is impossible, or unstable, or at least it would demand the planet to be very far away from its sun (which would quite certainly make it too cold for life, or even for there being a significant difference in temperature between the dark and the enlightned poles: both would be very close to 0 Kelvin).

Of course, you can always handwave that for narrative purposes.

Luís Henrique
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Nope, not with single axis rotation anyway. You can have what Uranus does where it rotates pretty much at right angles to the plane of the elliptic (its axis of rotation is tilted 97 degrees from the perpendicular) Summer is 20 years of daylight, winter 20 years of darkness, and spring and autumn are a year each in which the sun rises and falls, on average, every 9 hours. Now of course a world closer to its Primary those years will be days and the hours will be minutes but the effect will be the same.

Having said you can't do it, maybe you can; asteroids can "tumble" meaning that they describe transforms on multiple axes, we know of no planet which does this but theoretically it could happen. If such a planet had two axes of transformation one parallel to the elliptical and one perpendicular to it and those rotated at the right rates, the perpendicular transformation being on a 1:1 Spin-Orbit Ratio AKA tidally locked while the parallel one spins as fast or slow as you want, then the planet you describe is possible just improbable and really really weird.

The thing is that apart from Coriolis Effect and the fact that the stars will move across the sky where you can see them, in the frozen wastes of the dark side, this planet is in no way shape or form different from a normal tidally locked world that has a 1:1 Spin-Orbit Ratio on one axis like the Moon's orbit of Earth.

Edit: Sorry I forgot to note that you can only keep a rotating object in the "tumble" described with a constant input of torque, huge amounts of torque; on the scale of the lifetime energy output of a small yellow star every single orbit.

Edit: That's Ordinal Axes, Rotational Axis which would be moving constantly in relation to the planet.

Ash
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    Rigid bodies can nor have multiple axis of ritation – Taemyr Aug 04 '17 at 15:46
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    True, they can't for any long period of time, they settle onto a new axis of rotation, you'd have to keep disrupting it, oops. It makes no nevermind here the forces would be immense but Planet, even rocky ones Earth, behave more like water than rock on the cosmological scale. – Ash Aug 04 '17 at 16:41
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    No. Two axes of rotation=a single different axis of rotation. This holds for any rigid body. See Euler's rotation theorem. – Taemyr Aug 04 '17 at 17:30
  • @Taemyr Yes that's exactly what I did. – Ash Aug 04 '17 at 17:46
  • @Taemyr Sorry now I'm awake-ish and have actually read what I wrote instead of what I thought I wrote I understand where you were coming from. – Ash Aug 07 '17 at 11:21
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As discussed here, a sun technically can orbit a planet with a sufficiently small sun or large planet (at that point brown dwarf). By doing so, you can theoretically avoid the issues mentioned in the other answers by having the planet and the sun orbiting a third body.

DonielF
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Yes, but no. Basically, what you are asking for is a tilted axis planet that acts like a tidally locked world, and this just doesn't work. You can have the exact same on-planet conditions, except the part that always faces the sun would be better called the "east pole" rather than the south pole. If your planet has an axis of 0 degrees (I know this is the exact opposite of what you are wanting) and you have it rotating around its axis so slowly that it completes 1 revolution per orbit, you will have 1 side of the planet in eternal night, and the other side in eternal day, and both the north and south poles will both be in the thin borderlands between the two sides, so in the end you basically have an east pole and west pole in either eternal day or eternal night, but not a southern pole.

Alternatively, you can have a tilted axis world like Uranus, if you do this the day and night side will change throughout the year, in the spring and fall you will have have an equivalent day-night cycle on all parts of the world, and in summer one pole will be in eternal day only for it to switch halfway through the year in winter. You can have one or the other, but not both.

Now are these likely? Yes, very. Basically, a tidally locked world is probably more likely to exist around a red dwarf star, and it may be able to support an earth-like ecosystem in the borderlands between the day and night sides of the world. A high axis world is going to be very different, they can exist pretty much anywhere and be any size but will likely be naturally uninhabitable, the seasons are just to extreme. For your world, I wouldn't try and do something crazy. There is no particular reason for the planets south pole to always face the star, and to get the effect you want all you need to do is make the world tidally locked. My advice: Remove the high eccintricity and just make the thing tidally locked to a red dwarf star, or any type of star if it doesn't need to be habitable, this would preserve the feel of the world without requiring any gymnastics and doesn't require any significant suspension of disbelief.

skout
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How about a system like this one:

enter image description here

Left red-blue-thing beeing the sun's magnet. Right red-blue-thing beeing the planet's magnet. Grey beeing the planets orbital axis. Black beeing the magnetic field lines.

This would imply a torque to the planet. If tuned correctly, this might result in a torque to tilt the planets axis of rotation to just lock the planets poles.

I don't know how stable this is. (Should be a fun exercise for a physics undergrad)

Dominic Hofer
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So we've busted the myth that it is possible to have a spinning planet orbit a star within the Goldilocks zone while always pointing one pole toward the star.

Now we want to recreate the (planetary) conditions of the myth. The problem seems to be gravity and those pesky orbital mechanics. I really like @CandiedOrange 's idea of using the high energy jet of a black hole/quasar for a distant source of light and heat. Let's tweak it to be a bit more reliable and lot less lethal.

Put a nebula right in the path of a Quasar jet, so that a dense region heats up to near fusion temperatures. Now place a rogue planet near (or inside) the nebula so it's north pole points at the hot spot. Probably not in the path of the jet!

You can be creative about what the nebula and the fake star look like because of magnetic fields/turbulence or a wobble in the jet. (Would the nebula eventually become a glowing 'smoke ring' accelerating up the jet?)

maybeso
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A tidally locked planet will have its axis normal to the plane of its orbit. There is likely to be some libration so near the terminator there will be variations in light and dark. I suppose there might be a (geological) period before the lock was complete where the axis of rotation (period of rotation (becoming) identical to period of orbit) was slightly offset from that angle, and libration would be more interesting.

A Midgley
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Setting aside the questions of what tilted axis and tidally locked means, let's assume for a moment, that for whatever reason you have a planet where one of the poles always faces towards the sun.

Assuming that your planet is within the 'Goldilocks' zone of a star similar to Sol, your south pole would be not so much a desert as a barren wasteland (even deserts have life, this pole would not). Compare it to the daylight temperatures of Mercury. It is constantly having massive amounts of energy poured into it, across an extremely wide frequency spectrum.

Conversely, the energy being received by the dark side of the planet would be so low that it too would be lifeless, as an iceball - we are talking temperatures that would snap freeze anything biological that is exposed to them (the presence of a moon reflecting energy to the dark side will increase temperatures slightly, but not enough to support life).

So this leaves us with the equator. Will it be a narrow band of lush jungle? In short, no.

The extreme contrast of pressure and temperature colliding around the equator would result in a constant storm of truly epic proportions(well beyond anything ever seen on Earth) - a storm with constant winds fast enough to pick people up and throw them around like dolls. Assuming there is enough water on the planet to provide rain, the raindrops would move so fast they hit like bullets.

Short of magic or applied phlebotinum, this planet would be uninhabitable.

LuNatic
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    OP didn't ask how would life be on such a planet, but if such a planet is possible. Since you park the OP question and venture answering a question not asked, I dare to say you are not answering the question. – L.Dutch Aug 06 '17 at 14:13
  • Likely there would also be a flow of molten rock/metal from the hot side to the equator, so the tempest would probably make droplets of that to get suspended into the atmosphere (but would there be an atmosphere?) – Luís Henrique Feb 18 '18 at 19:40
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So let's say Earth is grazed by an enormous meteorite in a very particular fashion causing the axis to turn towards the sun. Not sure if this is possible, but I imagine that grazing it exactly on the north pole in the direction of the sun could cause this, while the gyroscopic effect would stabilize axis again. Let's call it "The Axident". For the sake of the thought experiment the meteorite has no additional effects.

We now have very intense seasons in between the poles and the tropics: a three month day in summer and a three month night in winter. I don't think the Earth's magnetosphere would be effective at this angle, so solar winds would also scorche the poles. The area around the equator, so between both tropics, would fare better. In Autumn and Spring pretty much nothing would change, Sun wise; similar angle though the sun is in the North in Autumn, same day length, same magnetic field protection. Winds would change, rain season would change. I'm not to sure what the Moon is doing, but probably tides would change too. Not a problem for much of the flora I would think.

Now before the Axident the equatorial area didn't really have Summer and Winter. Now it does. Pretty much like it is on the poles right now. Polar nights in Winter and midnight Sun in Summer. Intense stuff and very much a problem for most of the flora and fauna. This event would trigger an extinction event that eclipses the Holocene. Though surely enough plants will survive and adapt for life to continue. Oceanic life shouldn't be affected to much. Many land and lake animals will be in a bad situation. Birds can just fly wherever they like, so they should be good.

I think that Humans will also be to handle it best. But it never hurts to have a backup on Mars just to be sure.

Herman
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To me it sounds like the author of this question might be interested in a planet which axis is perpendicular to the rotation around the sun, not pointing towards the sun (as requested in the answer). If one rotation period of the planet is equal to the time it needs to circle the star, one side of the planet faces the star all the time and the other side always faces outer space. Of course, the warmest or coldest spots are not the geographic poles of the planet, but rather two opposite points on the equator. Naturally, there is no day/night cycle on such a planet.

This is in fact how the moon rotates around our earth. The same side always faces the earth. If you imagine the earth as a light source, this would pretty much roast the one side of the moon and leave the backside dark. But this is not the case because the sun and no the earth is the big light producer in the solar system.

I hope this answer helps!

Morn
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Logan is incorrect - If the planet it tidally locked it is still possible for it to spin as long as the axis of rotation is pointing towards its star. This means no day/night cycle. You could add a bit of wobble to that and maybe get some day/night cycles near the equator. Problem with this scenario (tidal locking) is that the star will heat the nearest pole enormously, and half the planet will always be in night (super cold). My guess is that the wobble wouldn't be enough to get much variation over the course of a single orbit, but this I'm not sure about.

RudeBoy
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  • Don't know why you were downvoted, this is a plot point in Interstellar which has pretty good science. – crobar Aug 04 '17 at 09:52
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    The axis of rotation for a tidally locked planet doesn't point towards the star, it's parallel to the axis of the orbit (perpendicular to the plane of the orbit). – Mark Aug 04 '17 at 10:36
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    (Which means that the pole cannot point towards the star during for the whole rotation - it can point towards the star once each orbit, like Uranus, or a side of the planet can point towards the star the whole time, but this side cannot possibly be a pole.) – Mark Aug 04 '17 at 10:39
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    By its very definition tidal lock requires the axis to be along the normal of the orbit (i.e. where we expect it to be with normal planets). Rotation around that axis is what makes the planet tidally locked. And Interstellar is an insult to every single movie that features pretty good science. – Peter Aug 04 '17 at 22:07
  • This is a good answer, but it should be a comment. OP ruled out having the planet tidally locked –  Aug 04 '17 at 23:09