APOD: Planets of the Solar System: Tilts... (2022 Sep 11)

[APOD Robot]

Planets of the Solar System: Tilts and Spins

Explanation: How does your favorite planet spin? Does it spin rapidly around a nearly vertical axis, or horizontally, or backwards? The featured video animates NASA images of all eight planets in our Solar System to show them spinning side-by-side for an easy comparison. In the time-lapse video, a day on Earth -- one Earth rotation -- takes just a few seconds. Jupiter rotates the fastest, while Venus spins not only the slowest (can you see it?), but backwards. The inner rocky planets, across the top, most certainly underwent dramatic spin-altering collisions during the early days of the Solar System. The reasons why planets spin and tilt as they do remains a topic of research with much insight gained from modern computer modeling and the recent discovery and analysis of hundreds of exoplanets: planets orbiting other stars.

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[MarkBour]

Hooray for Venus and Uranus, those non-conformists. Or is it because their names ended in "nus" that they decided to turn in uNUSual ways?

[Iksarfighter]

Could we guess Venus so slowed because it is internally liquid and has strong tidal forces from the Sun ?
Mercury must not be liquid as it is small.

[lazenby]

Could we guess Venus so slowed because it is internally liquid and has strong tidal forces from the Sun ?
Mercury must not be liquid as it is small.

if Venus changed its original rotation, the one set by the direction in which the protoplanetary disc rotated around the Sun, then Venus must have eventually spun down to no rotation at all. and if this occurred why would a braking force then begin spinning it up in the opposite direction?

[XgeoX]

Could we guess Venus so slowed because it is internally liquid and has strong tidal forces from the Sun ?
Mercury must not be liquid as it is small.

Mercury actually has a liquid outer core.
Venus is still a mystery, it might be practically all liquid, in-between or all solid. There’s not enough information yet about Venus’ geology to help.
There are three hypotheses in the mix for why Venus rotates so slow…
1. An impact with a very large object the size of a small planet (which might, or might not, have flipped it).
2. It could be a natural equilibrium from tidal forces from the sun slowing it down and the forces (wind) from the very thick dense atmosphere speeding it up.
3. Finally it could due to gravitational interaction with the other planets, including the exchange of angular momentum with Earth.
I hope I didn’t butcher those explanations too much!

Eric

[Tycho]

Would someone standing on Uranus see the ecliptic rise and set each day?

[De58te]

With regard to number 1, Venus being flipped over by "the inner planets .. most certainly underwent dramatic spin-altering collisions" as stated in the description, I remember an essay by Issac Asimov where he stated, if Venus suffered a monumental collision, then what imaginably incredible stroke of luck made it settle down into the most nearly perfect circular orbit of all the planets?

[Chris Peterson]

With regard to number 1, Venus being flipped over by "the inner planets .. most certainly underwent dramatic spin-altering collisions" as stated in the description, I remember an essay by Issac Asimov where he stated, if Venus suffered a monumental collision, then what imaginably incredible stroke of luck made it settle down into the most nearly perfect circular orbit of all the planets?

It can take a lot less energy to change the inclination of a body than it does to change its orbit.

[Sa Ji Tario]

Not everything is said, but it occurs to me that the tidal forces of the major planets, added to those of the Sun, induced (when the Earth and Venus were still in a gaseous state and in formation) that Venus is rotating opposite with respect to the Earth for being of almost identical masses

[Chris Peterson]

Not everything is said, but it occurs to me that the tidal forces of the major planets, added to those of the Sun, induced (when the Earth and Venus were still in a gaseous state and in formation) that Venus is rotating opposite with respect to the Earth for being of almost identical masses

When the planets were forming the accreting bodies that were coming together out of the orbiting accretion disk were certainly all rotating in the same direction. That of the rotating disk itself.

[orin stepanek]

planets of our solar system & 2 dwarf planets! Two planets spin
backward! Is that strange or most likely a normal anomaly!

A direct image of a multi-planet system around a Sun-like star. The
planets, TYC 8998-760-1 b and c, are visible middle and lower right.
Image credit: ESO/Bohn et al.

72a.jpg (10.01 KiB) Viewed 5997 times

Kitty's are doing research!

[MoonRockMan]

The way Jupiter's tilt is when spinning around its axis, would that mean that the Sun is low in the sky in the polar regions?

[johnnydeep]

The way Jupiter's tilt is when spinning around its axis, would that mean that the Sun is low in the sky in the polar regions?

Unless this is a trick question, the answer is yes! And the same goes for Mercury and Venus. All three rotate almost perpendicularly to the plane of their orbit around the Sun.

[MoonRockMan]

The way Jupiter's tilt is when spinning around its axis, would that mean that the Sun is low in the sky in the polar regions?

Unless this is a trick question, the answer is yes! And the same goes for Mercury and Venus. All three rotate almost perpendicularly to the plane of their orbit around the Sun.

No, not a trick question! haha I suspected as such but I wasn't sure. Thank you so much for the confirmation and explanation, and the Mercury/Venus info too.

[Sa Ji Tario]

Not everything is said, but it occurs to me that the tidal forces of the major planets, added to those of the Sun, induced (when the Earth and Venus were still in a gaseous state and in formation) that Venus is rotating opposite with respect to the Earth for being of almost identical masses

When the planets were forming the accreting bodies that were coming together out of the orbiting accretion disk were certainly all rotating in the same direction. That of the rotating disk itself.

Due to some school induction experiments, it occurred to me that the Earth-Venus induction of the major planets might have caused them to shift that of Venus in favor of Earth.
Y mil gracias

[XgeoX]

planets_iau.jpg
planets of our solar system & 2 dwarf planets!
Kitty's are doing research!

Uh they prefer to be called “little” planets
Adorable kitties as usual, your pics always bring a smile to my face.

Eric

[orin stepanek]

planets_iau.jpg
planets of our solar system & 2 dwarf planets!
Kitty's are doing research!

Uh they prefer to be called “little” planets
Adorable kitties as usual, your pics always bring a smile to my face.

Eric

I never did like that the planet status was changed! To me a planet is a planet! At least Ceres got some attention!
I get the animal photos from the dialog!

[XgeoX]

planets_iau.jpg
planets of our solar system & 2 dwarf planets!
Kitty's are doing research!

Uh they prefer to be called “little” planets
Adorable kitties as usual, your pics always bring a smile to my face.

Eric

I never did like that the planet status was changed! To me a planet is a planet! At least Ceres got some attention!
I get the animal photos from the dialog!

I’m with you, I say if it’s round and not a moon it’s a planet!

[Ann]

Uh they prefer to be called “little” planets
Adorable kitties as usual, your pics always bring a smile to my face.

Eric

I never did like that the planet status was changed! To me a planet is a planet! At least Ceres got some attention!
I get the animal photos from the dialog!

I’m with you, I say if it’s round and not a moon it’s a planet!

(Dwarf?) planet Ceres. Image Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / Justin Cowart

---

(Dwarf?) planet Pluto. Credits: NASA/JHUAPL/SwRI.

Well, Ceres is round and it is not a moon, so... Welcome to planethood, Ceres!

Although I have to admit that Pluto is a heck of a lot more impressive as a planet than Ceres is.

Ann

[orin stepanek]

I never did like that the planet status was changed! To me a planet is a planet! At least Ceres got some attention!
I get the animal photos from the dialog!

I’m with you, I say if it’s round and not a moon it’s a planet!

Well, Ceres is round and it is not a moon, so... Welcome to planethood, Ceres!

Although I havde to admit that Pluto is a heck of a lot more impressive as a planet than Ceres is.

Ann

Pluto is very impressive indeed! It has a lot of characteristics for future exploration!

[johnnydeep]

I’m with you, I say if it’s round and not a moon it’s a planet!

Well, Ceres is round and it is not a moon, so... Welcome to planethood, Ceres!

Although I havde to admit that Pluto is a heck of a lot more impressive as a planet than Ceres is.

Ann

Pluto is very impressive indeed! It has a lot of characteristics for future exploration!

I just consider all these things to be "Planetary Mass Objects" and leave it at that.

A planetary-mass object (PMO), planemo,[1] or planetary body is by geophysical definition of celestial objects any celestial object massive enough to achieve hydrostatic equilibrium (to be rounded under its own gravity), but not enough to sustain core fusion like a star.[2][3]

The purpose of this term is to refer to a broader range of celestial objects than the concept of planet, since many objects similar in geophysical terms do not conform to typical expectations for a planet. Planetary-mass objects can be quite distinguished in origin and location. Planetary-mass objects include dwarf planets, planetary-mass moons or free-floating planemos, which may have been ejected from a system (rogue planets) or formed through cloud-collapse rather than accretion (sometimes called sub-brown dwarfs).

[Chris Peterson]

Well, Ceres is round and it is not a moon, so... Welcome to planethood, Ceres! 😀

Although I havde to admit that Pluto is a heck of a lot more impressive as a planet than Ceres is.

Ann

Pluto is very impressive indeed! It has a lot of characteristics for future exploration!

I just consider all these things to be "Planetary Mass Objects" and leave it at that.

A planetary-mass object (PMO), planemo,[1] or planetary body is by geophysical definition of celestial objects any celestial object massive enough to achieve hydrostatic equilibrium (to be rounded under its own gravity), but not enough to sustain core fusion like a star.[2][3]

The purpose of this term is to refer to a broader range of celestial objects than the concept of planet, since many objects similar in geophysical terms do not conform to typical expectations for a planet. Planetary-mass objects can be quite distinguished in origin and location. Planetary-mass objects include dwarf planets, planetary-mass moons or free-floating planemos, which may have been ejected from a system (rogue planets) or formed through cloud-collapse rather than accretion (sometimes called sub-brown dwarfs).

Classification is, by its nature, hierarchical. PMO represents a high-order category, with "planet" below it, and planet types (dwarf, gas, terrestrial, ice, etc) below that.

[johnnydeep]

Pluto is very impressive indeed! It has a lot of characteristics for future exploration!

I just consider all these things to be "Planetary Mass Objects" and leave it at that.

A planetary-mass object (PMO), planemo,[1] or planetary body is by geophysical definition of celestial objects any celestial object massive enough to achieve hydrostatic equilibrium (to be rounded under its own gravity), but not enough to sustain core fusion like a star.[2][3]

The purpose of this term is to refer to a broader range of celestial objects than the concept of planet, since many objects similar in geophysical terms do not conform to typical expectations for a planet. Planetary-mass objects can be quite distinguished in origin and location. Planetary-mass objects include dwarf planets, planetary-mass moons or free-floating planemos, which may have been ejected from a system (rogue planets) or formed through cloud-collapse rather than accretion (sometimes called sub-brown dwarfs).

Classification is, by its nature, hierarchical. PMO represents a high-order category, with "planet" below it, and planet types (dwarf, gas, terrestrial, ice, etc) below that.

Reading the wikipedia article on dwarf planet made my head hurt. I'd like to see a definitive hierarchical classification chart showing all the different types of solar system objects and how they relate.

[Chris Peterson]

I just consider all these things to be "Planetary Mass Objects" and leave it at that.

Classification is, by its nature, hierarchical. PMO represents a high-order category, with "planet" below it, and planet types (dwarf, gas, terrestrial, ice, etc) below that.

Reading the wikipedia article on dwarf planet made my head hurt. I'd like to see a definitive hierarchical classification chart showing all the different types of solar system objects and how they relate.

"Dwarf planet" as officially (IAU) described is an absurdity. How can a dwarf planet not be a planet? Logically, "dwarf" should be seen as a qualifier like "terrestrial" or "gas giant". Really silly.

Rationally, "planet" should define any body that is sufficiently massive to form a spherical shape under its own gravity and which orbits a star (or originated in orbit around a star). From there we can further classify them. That whole "clears its orbit of debris" qualification is pretty useless and pointless.

[johnnydeep]

Classification is, by its nature, hierarchical. PMO represents a high-order category, with "planet" below it, and planet types (dwarf, gas, terrestrial, ice, etc) below that.

Reading the wikipedia article on dwarf planet made my head hurt. I'd like to see a definitive hierarchical classification chart showing all the different types of solar system objects and how they relate.

"Dwarf planet" as officially (IAU) described is an absurdity. How can a dwarf planet not be a planet? Logically, "dwarf" should be seen as a qualifier like "terrestrial" or "gas giant". Really silly.

Rationally, "planet" should define any body that is sufficiently massive to form a spherical shape under its own gravity and which orbits a star (or originated in orbit around a star). From there we can further classify them. That whole "clears its orbit of debris" qualification is pretty useless and pointless.

Pleased to hear you say that. I always hated the "clearing its orbit" attribute. And, yeah, a "baby human" is clearly still a human! Now, let's hear it for all the dwarf terrestrial rogue exoplanets out there!