As far as we know Earth and every other planet in the solar system rotate around their axes. Whether it be Uranus which rotates on its side or Mercury which rotates perfectly straight, all planets spin the same way. However, what if the planets rotated up and down? To explain this imagine if Canada slowly moved northward towards the north pole and once crossed started going south into the southern hemisphere and once it reached the south pole it started going north, Tl.dr the planet rotates longitudinally instead of latitudally. Is it possible?

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    $\begingroup$ The current rotation is what defines longitude and latitude. You can spin a globe any way you like but that just redefines where the polls are. What you were contrasting before is how that relates to the planets orbit. That’s a different thing. $\endgroup$ – candied_orange May 21 '20 at 17:26
  • $\begingroup$ This was quite similar to one of my high school physics quizzes - it's about simple vector addition. Many online tutorials about it. $\endgroup$ – user535733 May 21 '20 at 18:16

No. The way we define latitude and longitude is based on the planet's axis of rotation. You can certainly (AFAIK) have a planet with a 90° axial inclination, or (probably) a planet that is identical to Earth except with all the land masses rotated 90°, but unless you completely change the definition of "pole", the poles will, by definition, be stationary w.r.t. the planet's rotation.

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    $\begingroup$ Ah, the mathematician's answer! $\endgroup$ – jdunlop May 21 '20 at 17:28
  • $\begingroup$ Well, the OP did say "the planet rotates longitudinally instead of latitudinally", and no, by our present definitions, that's not possible by definition. $\endgroup$ – Matthew May 21 '20 at 17:30
  • $\begingroup$ OP uses a neologism and is defeated by semantics. How surprising. $\endgroup$ – Mazura May 22 '20 at 13:32
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    $\begingroup$ @Mazura, the OP's question was basically 'can I completely ignore the definitions of "rotational axis", "pole" and "latitude / longitude"'... Well, yes, you can, but I don't recommend it, because a) what's the point? and b) you'll likely just confuse your audience. The only alternative that comes to mind is wanting the poles to move at a non-geological pace and/or have multiple axes of rotation. (But that's not how the question is phrased, and anyway, see Halfthawed's answer for that...) $\endgroup$ – Matthew May 22 '20 at 15:08

I'm going to assume that the question you're asking is 'Can the Earth additionally rotate up-and-down?', because, Matthew's answer has pointed out, we define 'up and down' based on the planet's already spinning axis. The only way this question makes sense is that you're asking whether the Earth can additionally spin up-and-down. And the answer to that is a clear 'No'.

This goes more into it, the short of it is that multiple vectors in a closed system will eventually become a single vector and basically the Earth will spin diagonally from our current perspective.

  • $\begingroup$ The link you reference is about impossibility of some other specific case, but then it references torque-free precession, which could create some fancy rotation if the body was not rotationally symmetrical. It happens with asteroids a lot, but since a planet is defined as a body in hydrostatic equilibrium, you could only have asymmetrical planet for a short (on geological timescales) time after a collision with another large body. $\endgroup$ – Jan Hudec May 22 '20 at 20:40

As you say, Uranus does. All it would mean is that the axial tilt would be 90 degrees. This is unlikely in the course of normal planetary formation, so (as with Uranus) it would probably take a series of impacts early in the planet's history to point its axis in the appropriate location.

Now, if we're talking about Earth, things would obviously look a lot different. The north and south poles would be two points on what is currently the equator, and the ice caps would be there as well. Also, given that this would've been the case for most of the planet's history, the equatorial bulge would have moved as well.

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    $\begingroup$ I'm not sure you'd get ice caps on spots that face the sun half the year. (That said, you'd get some really interesting climates on a planet like this...) $\endgroup$ – Matthew May 21 '20 at 17:28
  • $\begingroup$ No not in the way uranus orbits beacause it still rotates on its axis just on its side. $\endgroup$ – Nanoshadow May 21 '20 at 18:31
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    $\begingroup$ @Nanoshadow - whatever a planet rotates around is its axis. It doesn't matter which direction it rotates, it will have an axis. $\endgroup$ – jdunlop May 21 '20 at 18:33
  • $\begingroup$ @nano If Earth rotated such that Canada went north and then south, that would put the polls at roughly Malaysia and Brazil. It would then be oriented on that axis. $\endgroup$ – SRM May 22 '20 at 14:01

Yes, for a given definition of 'North Pole'.

You see, there are three different 'North Pole's

  • Geographic North Pole, which is defined as 'the point in the Northern Hemisphere where the Earth's axis of rotation meets its surface' (ignoring precession).
  • Magnetic North Pole, defined as 'the point on the surface of Earth's Northern Hemisphere at which the planet's magnetic field points vertically downwards'. This is what your compass points at.
  • Geomagnetic North Pole: the Magnetic North Pole and Magnetic South Pole are not actually directly opposite each other. This is the closest approximation to 'but, what if they actually were?'

As should (hopefully) be pretty obvious, the first definition is completely incompatible with your question: as soon as you move the axis of rotation, the Geographic North Pole moves with it. Canada cannot, by definition, rotate through the Geographic North Pole, and on down to the Geographic South Pole.

However, the Magnetic and Geomagnetic North Poles move. They are also largely independent of the Axis of Rotation. In the 1850s / 1860s, they actually got all the way down to King William Island in Canada - that's a quarter of the way to the equator! And, sometimes, Magnetic North is in the Geographic South.

So, you could (theoretically) have a situation where Magnetic North was pretty much on the equator. Countries could then rotate 'North' (Magnetically) past the Pole, and continue 'South'. However, they are still rotating around the planet's axis: For Magnetic North to be roughly where Geographic North currently is, and Canada to rotate through it, you would need the Geographic North Pole (or the Geographic South Pole) - and the Earth's Axis - to be somewhere around Cape Town

It should be noted, of course, that this would make Canada nice and warm, while Hawaii would be covered in ice.


Unlikely - but Yes

So taking this question to be "Could a planet rotate around an axis in the elliptic and tangential to its orbit?" The answer is:

"Sure - but it takes very specific setup."

So the planets all rotate because the swirling cloud of gas that they formed from rotated. Momentum is conserved, and there is nothing that opposes this motion.

Since the gas cloud started as a disk, the planets all start rotating in the same direction - on an axis that intersects the elliptic at a right angle.

You get something like Uranus because some large impact or series of interactions basically tilted the planet over 90 degrees. Now the axis is along the plane of the elliptic, and points towards the sun. The planet appears on its side.

To get a planet that rotates "Up and down" as OP described, you would need a second interaction or series of interactions that would change the axis of rotation be another 90 degrees in a different plane.

So you would now have to rotate the axis from pointing at the sun, to tangential to the sun.

Obviously these two interactions are very specific and very energetic, and would therefore be extraordinarily unlikely. But in a large enough universe of cases it could happen.


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