The Mysterious Shape of Jupiter: Why Gas Planets Stay Spherical

[timothychoi]

TL;DR

If Jupiter is made of gas, how can it maintain its shape without being contained in a spherical shaped container?

If Jupiter is made of gas, how can it maintain its spherical shape without being contained in a spherical shaped container?

 

[mjc123]

Gravity. The lowest-energy shape for a mass of gas held together by its own gravity is a sphere.

You mustn't think in terms of lab-based definitions, such as "a gas expands to fill its container". That refers to very small amounts of gas whose self-gravity is negligibly small. A mass of gas the size of Jupiter will be held together by its own gravity.

 

[Orodruin]

The same goes for stars. Stars are much hotter than Jupiter but also remain close to spherical due to self-gravity.

 

[MikeeMiracle]

Certain shapes you see repeated many times over in nature as they are the most efficient. Anything made of gas in space or anything molton will become a sphere. Another example is a hexagon, look at how the rock cooled after a volcanic eruption at the "Giants Causeway" in Ireland. Similarly bees make hexagons as it is the most efficient way of making the hive that maximises space available for the least amount of wax used to create it.

 

[sophiecentaur]

The gas surrounding Jupiter is held in by the same force that keeps our atmosphere around the Earth. Our atmosphere is held in quite firmly and Jupiter's even more so, due to the incredible mass involved.

Also, the description "Gas Giant" is a bit misleading. Its not whispy stuff all the way down. There is probably a rocky but not solid core and a large amount of liquid 'metallic hydrogen' above it. This link gives a description of the likely arrangement.

 

[HankDorsett]

The gas surrounding Jupiter is held in by the same force that keeps our atmosphere around the Earth. Our atmosphere is held in quite firmly and Jupiter's even more so, due to the incredible mass involved.

Also, the description "Gas Giant" is a bit misleading. Its not whispy stuff all the way down. There is probably a rocky but not solid core and a large amount of liquid 'metallic hydrogen' above it. This link gives a description of the likely arrangement.

I guess I should have read down to this post before I did some internet "research". I originally struggled to see how Jupiter could exist without a solid core. What I found matches what you posted.

 

[sophiecentaur]

There's a certain logic to Jupiter's form. If you take a mass of general 'gas and stuff' (part of the primordial nebula from which the Solar System was formed) equal to Jupiter's mass, all the more dense stuff will end up in the middle, displacing the lighter gas etc. The total mass and the proportions of all the stuff in it will determine its radius.
I still think it's incredibly smart how the details of a structure like that are deduced, when you realize that, so often, there is evidence, later that confirms it all.

 

[Ophiolite]

Also, the description "Gas Giant" is a bit misleading. Its not whispy stuff all the way down. There is probably a rocky but not solid core and a large amount of liquid 'metallic hydrogen' above it. This link gives a description of the likely arrangement.

Research in the following decade confirmed this view, for example this paper based on Juno data. However, in an effort to resolve conflict between Juno and Galileo observations, these authors "confirm that Jupiter’s structure must encompass at least four different regions: an outer convective envelope, a region of
compositional, thus entropy change, an inner convective envelope and an extended diluted core enriched in heavy elements, and potentially a central compact core". [Emphasis added]

Aside: it would be preferable to describe the core as enhanced with heavy elements derived from rocky antecedents rather than "rocky". (Excuse the geological pedantry - its genetic.)

 

[sophiecentaur]

(Excuse the geological pedantry - its genetic.)

Bring it on. Where would we be without a bit of pedantry?
I guess you bridled at my use of the term "stuff" but it seemed to fit here.

 

[Vanadium 50]

Excuse the geological pedantry - its genetic

Technically, wouldn't it be zeusological?

 

[mjc123]

Diological - very irregular noun (Zευς, Zευ, Δια, Διος, Διι).

 

[Klystron]

Technically, wouldn't it be zeusological?

Jovian? Zeusological sounds so close to zoological, by Jove.

 

[sophiecentaur]

Lemme out of here!

 

[Ophiolite]

Bring it on. Where would we be without a bit of pedantry?
I guess you bridled at my use of the term "stuff" but it seemed to fit here.

No, I liked the stuff. I'm all for stuff! Stuff is good. It was calling it rock, when it's lost all rock like attributes, that kept nagging at me, till I resolved it with the post. :)

Technically, wouldn't it be zeusological?

Perhaps, but geologists have a plan to take over the Universe, one planet at a time.

 

[sophiecentaur]

Perhaps, but geologists have a plan to take over the Universe, one planet at a time.

And they will need a different name for themselves for each planet they take over. Poor planning, imo.

 

[Klystron]

Partial planetary table using Roman names.

Planet​	modifier​
Mercury Venus Earth Mars Jupiter Saturn	mecurial venusian terran martian jovian saturnine

 

[sophiecentaur]

Wot no Vulcan?

 

[geordief]

Diological - very irregular noun (Zευς, Zευ, Δια, Διος, Διι).

That is impressive. Where did you come across those forms?

Easily confused with θεός in the genitive there.

My Greek is ancient and poorly preserved.

 

[DaveC426913]

Jupiter is not a sphere; it is an oblate spheroid. It has been bloated at the equator by its own rotation.

Same goes for Saturn.
And - not to put too fine a point on it - Earth too.

 

[sysprog]

Jovian? Zeusological sounds so close to zoological, by Jove.

If you're going with Latin, instead of Greek, Jovian corresponds to Terran.

 

[mjc123]

The Latin adjective tends to be used with general reference to the planet (the Martian atmosphere, the Jovian satellites etc.). The more specific analogy with geology tends to use the Greek form, e.g. selenology (the "geology" of the moon), areology (Mars). Proceeding by analogy, I suppose we would have hermology, aphroditology, diology, kronology (not to be confused with "chronology"), ouranology, poseidonology, and plutonology (perhaps also charonology). Oh yes, and hephaestology for Vulcan...

 

[Vanadium 50]

Pluto is Roman. It's also been unfriended from the list of planets, but that's another story. Hadenology?

 

[sysprog]

It's also been unfriended from the list of planets

HaHaHa

 

[mjc123]

Just come across the term "kronoseismology, or the ability to see what's happening inside Saturn":
https://www.nationalgeographic.com/...-is-day-on-saturn-astronomers-just-found-out/

 

[Dnj23]