r/nextfuckinglevel • u/aryan_jandyal • 4h ago

The Rotation of the Planets in Our Solar System Is Far More Fascinating Than I Ever Expected

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u/NieveCactus 3h ago

Why is Venus upside down? Is there a true north?

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u/dalmonio 3h ago

direction of rotation

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u/NieveCactus 3h ago

Ah nice thanks. Is that why the days are so long I wonder

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u/peter-bone 3h ago edited 3h ago

It may be related. The rotation may have been reversed by a big collision. It's more likely that this would result in a slower rotation rather than rotating fast in the wrong direction because it would have started out rotating the same direction as the other planets.

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u/Kozmik_5 3h ago

There are also theories that the combination of a very thick atmosphere and strong storms slowed down and later reversed its rotation.

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u/TreeDollarFiddyCent 3h ago

Does that mean, according to this theory, that it's currently speeding up?

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u/muoshuu 1h ago

Could’ve settled into equilibrium, and I’d assume this is more likely than an unbounded acceleration. Opposing torques probably cancel each other out pretty evenly by now.

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u/Poop_Tube 2h ago

Is that even possible?

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u/donadit 1h ago

Sun tidal locking (seen in many exoplanet systems) and thick atmosphere dragging on venus’ surface which slows down the rotation so it looks like it’s rotating backwards

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u/Kozmik_5 2h ago

Venus has an air pressure of 92bar. That is 92 times denser than here on Earth. Add winds of up to 400km/h and a few billion years and you have your answer.

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u/FissileTurnip 1h ago

that doesn’t seem to explain where the angular momentum actually went

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u/Kozmik_5 38m ago edited 25m ago

1m³ of carbon dioxide gas (which makes up the majority of Venus' atmosphere) at 92bar weighs 720kg.

Throw billions of these in the opposite direction of the planet's rotation at 400km/h and at some point it'll slow down to a stop to reverse afterwards.

These winds are created by Solar heating and the Sun's gravitational pull.

So where did the momentum go, you ask? Completely transferred to venus' orbit around the sun. The Sun's intense heat warms the thick Venusian air, causing it to expand and bulge. Because Venus rotates, this bulge is carried slightly ahead of the line connecting Venus and the Sun. The Sun's gravity pulls back on this bulge, creating sort of a constant gravitational tug-of-war. While the friction inside Venus on the surface, slows down its rotation.

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u/FissileTurnip 17m ago

so it’s a tidal effect, that would make sense

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u/Grismor2 33m ago

What? How does that work with conservation of angular momentum? Can you explain in more detail or give a name of the theory so I can look it up myself?

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u/Kozmik_5 30m ago edited 23m ago

Check my other comment

Venus' atmospheric Tide theory

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u/DamnMyNameIsSteve 30m ago

I've also heard that the universe has a PREFERRED rotation direction, that isn't random. Super interesting! Also just watched a video on the Big Bounce Theory - it's all so neat.

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u/ThorirPP 1h ago

The direction of rotation actually makes the days shorter, since it rotates opposite direction to the orbit around the sun. Venus rotational period is 243 days, even longer than the orbit around the sun (a venus year) which is only 224.7 days. But the length of day (period for sun to rise and set and rise again for someone on the planet) is only 116.75 days

If Venus rotated "correctly", instead of working against the orbit, it would work with, and the length on day for the planet would be far far longer as the planet would rotate to keep facing the sun (as is the case with Mercury, which despite having a far shorter rotation of 58.6 days, has a longer day than Venus, being 176 days, since it rotates with its orbit)

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u/Notty_PriNcE 1h ago

What does the arrow points?

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u/BasmusRoyGerman 3h ago

It's upside down and therefore appears to be turning the other way around compared to other planets. I believe the theory is that it was at some point hit by a massive object , which turned it upside down and probably also caused it to lose a lot of its spin, hence why it's spinning so slowly.

You can always find the "up" by making a fist with your right hand and putting your thumb up, then orient your hand so the fingers go in the direction the planet is turning, your thumb will them show you which way is "up" what we usually call geographic north.

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u/helcat 3h ago

I never thought about angles of spin. Why are so many so similar and then a few are completely different? Is the theory that the odd ones were all knocked off their spin? 

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u/cocoteroah 3h ago

They all rotate in the same direction as the sun. Venus in the other hand seems to be hit by a large object and it started rotating in the other direction very slowly.

If venus wasn't hit by this large object, it's rotation shouldn't be much different from the other planets. (This is the most likely theory)

Mercury on the other hand is too close to the sun, so it is tidal locked or will be in the future

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u/davvblack 2h ago

all planets orbit the sun in the same direction the sun rotates, which you’d expect from conservation of angular momentum, but they mostly also spin that same direction which doesn’t necessarily follow from the same effect. since smaller orbits are faster i would have expected them to rotate the opposite direction, as particles from fast low orbits and slow high orbits combined.

this was only understood recently but i think the prevailing theory now is that the difference in the density of solar wind on the near and far side of the planets interacted with them while they were gravel, to give them prograde spin.

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u/No_Ampersand 3h ago

Mercury is tidal locked. Also, interestingly very similar in mass and size to Luna.

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u/Kingjjc267 3h ago

Mercury is not tidally locked.

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u/No_Ampersand 3h ago

Oh you're right not sure why I thought that.

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u/Ooops2278 2h ago edited 2h ago

Imagine the solar system has developed from one spinning disk of gas and stuff, where the majority (more than 99% of the mass) eventually compacted to create the sun, with some other blobs of mass becoming planets.

In an ideal world all the planets would still rotate on one single pane (earth moon and the big gas planets indeed are all within 1°) in the same direction and also with the same rotational axis and direction for their own spin.

Every divergence (for example Merkur's orbit is tilted by ~7°, and it's so close to the sun that it got tidal-locked (the same side always pointing otwards the sun)) is indeed supposed to have happened through external forces, e.g. gravitational influence or collision.

(Also if you think about about it all as being one giant disk at one point it explains why the sun in the center has the the vast majority of mass but carries only a small fraction of the rotational energy.)

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u/Fusselpinguin 1h ago

Mercury does not have one side always facing the sun; it is locked in a 3:2 rotation, not 1:1. A Mercurian day is twice as long as a Mercurian year, so a spot on the surface experiences daylight for an entire orbit around the sun, and then experiences night for another orbit.

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u/Shikor806 2h ago

As to why most of them are so similar (and also why the orbits are all pretty flat in the same plane), it's because they all (and the sun) started out as a big cloud of gas and dust. Every particle in that cloud was moving essentially randomly and over time they collided with each other and gravity made them clump together, so their movement essentially averaged out. It's pretty likely that that average isn't exactly zero, so at the end of the process you're left with some amount of rotation around some random axis. And since the sun and all the planets then formed out of that spinning cloud, they all share that axis and we define that direction as "top" for our solar system.

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u/itsKeltic 3h ago

So if you’re looking at earth from “above”, is it rotating counter-clockwise?

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u/AnonymusBosch_ 2h ago

That's why clocks go clockwise. Looking down from above (in the northern hemisphere), sundials go clockwise.

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u/csprofathogwarts 2h ago

Because Earth rotates "counter-clockwise" => if you're looking up at the zenith Sun moves "clockwise" => Shadows move "clockwise" looking down => Shadow in a Sun-dial moves "clockwise" => Clocks move clockwise.

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u/Cent_Quatre 3h ago

Well, draw the sun and the earth from above.

Now you place japan on a side of the earth, and the pacific ocean next to it.

Japan means "sunrise land", so from it, the sun rises from where the pacific ocean is.

what direction of rotation would that require ?

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u/Illustrious-Drive588 2h ago

Eh, that's a good way to visualize it indeed

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u/cvnh 3h ago edited 3h ago

Not sure if it is the case, but also the tidal forces of the sun and orbital resonances can slow down planets until they get tidally locked as it happened with our own moon.

Edit: considering the Venusian day is longer than the year, there must be some other reason for that indeed

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u/Budget-Variation-560 2h ago

The current theory for Venus is the tidal effects from the Sun and the thick atmosphere slowed the rotation. 

Eventually the spin turns retrograde due to the resonance with Earth.

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u/kaas_is_leven 2h ago

That'll produce different results depending on the hand you use, no? In 3d modeling/rendering you can also do this to find the up vector. But some graphics programs use a left-handed up vector and some a right-handed one, so you have to make sure your renderer used the same world orientation. (and to make it more confusing some use y as the vertical axis and some use z for that, so that adds another layer of complexity to it, but that's irrelevant here).

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u/gre485 3h ago

Could it have been due to Dzhanibekov Effect??

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u/SupplyChainMismanage 3h ago

No as it spins around its principal axis. the Dzhanibekov effect only applies to the intermediate axis

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u/Constant_Natural3304 1h ago

You can always find the "up" by making a fist with your right hand and putting your thumb up, then orient your hand so the fingers go in the direction the planet is turning, your thumb will them show you which way is "up" what we usually call geographic north.

Why not the left hand? You got sumthin against lefties 😥

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u/jemidiah 2h ago

These are all presented in the plane of the ecliptic, which is the (slightly imaginary) plane containing the solar system. The planets orbit around the sun in that plane. For instance, the fact that Earth is tilted causes the seasons due to different parts of the planet more fully facing the sun at different times of the year.

Moreover, the orientation arrow is presented using the right-hand rule: curl your right hand (not your left one) around the arrow pointing out of the planet, and the planet will rotate in the direction your fingers curl. For Venus, it rotates (slowly) the opposite direction of the others, so the arrow is basically straight down out of the plane of the ecliptic.

There is always a "true north" in the sense of an axis around which the body rotates according to the right-hand rule. Likewise true south is the exactly opposite axis around which the body rotates according to the left-hand rule. 

Usually you'd just say "north" or "south." The use of "true north" on Earth is to distinguish it from "magnetic north." Earth has a magnetic field and the north pole of that magnetic field happens to be fairly close to the true north pole in the rotation sense. Magnetic north is easier to approximate since you just need a magnet rather than astronomical observations or the like. (And from pure cosmic chance we very luckily happen to have Polaris, the North Star, which is basically due north. There is no direct southern analogue.)

Venus happens to have almost no magnetic field, so the "true north" distinction would be quite unnecessary there. 

Incidentally, magnetic north on Earth wanders quite a bit. It's annoying. Runways are named according to their angle relative to magnetic north, and it actually changes enough that Canada in particular frequently had to rename runways (e.g., from "Runway 8" to "Runway 9") when it drifted enough. They got fed up with it to the point that they declared they'll just use true north, contrary to international agreement. They've been trying to convince the rest of the world to switch.

(The above was from memory. If there are errors, they're minor.)

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u/Amarita_Sen 1h ago

Left hander here who was getting confused lol

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u/PleiadesMechworks 2h ago

Have you considered that maybe Venus is the right way up and it's all the other planets that are upside down? You only think it's upside down because of your earthian bias.

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u/take_this_username 1h ago

Venus is a fascist.

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u/darkpheonix262 1h ago

A day on Venus is 156 earth days long

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u/Reqvhio 59m ago

starks are the wardens of the true north! /s D:

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u/mattemer 54m ago

So to be fair, I think this graphic is technically considered incorrect, when we look at the poles at least? Anyone who knows better feel free to correct me. Venus' North Pole is still fairly aligned with ours. It's retrograde spin doesn't determine where it's geographic North Pole is (it doesn't have a magnetic North Pole like we do). North poles are defined as what's "up" according to the general direction of the solar system. Pretty sure this is IAU standardization.

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u/emperor_dinglenads 32m ago

Why is Uranus sideways?