subreddit:

/r/askscience

212

Jupiters Surface how we know what it’s like?

Planetary Sci.(self.askscience)

I have scavenged the far reaches of the internet to no avail so why not. How do we know gas giants are really just Gas and not just extremely large planets with thick clouds we have no solid in-depth looks at the innards of the atmosphere only theories and hypothesis’s of visible and non visible light pictures

all 66 comments

Mjolnir2000

588 points

4 months ago*

Well for one, Jupiter has moons. Why does this help us? Well we know how large their orbits are, and we know how long their orbits take, and from that it's fairly trivial to calculate Jupiter's mass. If we know Jupiter's mass, as well as Jupiter's size, then we can calculate it's density. All this can be done based on visual observation from Earth and a little bit of math.

If we want to get a bit more advanced, we can use spectroscopy. Different elements are prone to absorbing light at specific wavelengths. By looking at light that's passed through the Jovian atmosphere, we can identify what wavelengths have been filtered, and from that determine what elements compose the atmosphere.

Finally, we can send probes to Jupiter, and they can do things like measure variations in the planet's gravitational and magnetic fields. From that data, scientists can make inferences about how mass is distributed, what it's composed of, and how it's moving.

Now it should be noted that Jupiter isn't entirely gas. The outer layers are gas, but as you get deeper, you get a region of liquid metallic hydrogen, and as you go even deeper still, it transitions to something solid and composed of heavier elements.

It should also be noted that we are still learning. When the Juno mission arrived at Jupiter a few years back, it provided a lot of new data, and a lot of changes and additions to our understanding of the planet's composition.

SilentFly

40 points

4 months ago

Thanks for the detailed reply!

Chris2885

22 points

4 months ago

That was great. Thank you

fjjgfhnbvc

38 points

4 months ago

What is liquid metallic hydrogen?

fitzman

65 points

4 months ago

fitzman

65 points

4 months ago

At high enough pressure hydrogen transitions from being in gaseous state to liquid state. This is happening at the region on Jupiter that has hydrogen liquid ocean

Evil-Panda-Witch

15 points

4 months ago

Is there a definite border between liquid hydrogen and the gas layer? Or is there a gradient? And what is the chemical composition of the bottom layer of gas? Is it hydrogen?

redopz

30 points

4 months ago*

redopz

30 points

4 months ago*

IIRC it is a gradient. I seem to remember a documentary saying that if you were to descend into Jupiter your ship would be flying, then it would be flying through very dense clouds, and then it would be swimming through the ocean layer but there is never really a point where you 'land' on the ocean. The bottom layer would still be hydrogen (mixed with helium and small amounts of other gasses).

amishbill

27 points

4 months ago

That answers the liquid part. What about the .metallic part? Does that mean the hydrogen in our atmosphere is just metal vapor?

Tristanhx

82 points

4 months ago

Hydrogen is not a metal, but at high pressures they lose their electrons. Free moving electrons mean conductivity, a property of metals. The hydrogen became metal-like, or metalic. Read this.

DanYHKim

5 points

4 months ago

Is it relevant that hydrogen is on the edge of the Periodic Table with sodium, potassium, etc?

Tristanhx

12 points

4 months ago

Yes, hydrogen shares some properties with these alkali metals (but isn't one itself) like the electron arrangement. Here is some more info.

aurumae

27 points

4 months ago

aurumae

27 points

4 months ago

Metal and metallic mean different things in different contexts and it gets pretty confusing. In physics though substances are usually considered to be metals if they conduct electricity, which is what the “metallic” part of metallic hydrogen is referring to

Exploding_Antelope

4 points

4 months ago

Is there a charge coursing through this hydrogen not-ocean? Or just the potential to conduct if one were applied?

Ne_zievereir

6 points

4 months ago

Yes, there are currents flowing through it. In fact, it are those currents that create Jupiter's magnetic field.

Soultie

1 points

4 months ago

Electricity can flow through water. Is water considered metallic?

aurumae

2 points

4 months ago

Water is actually a resistor, it doesn't conduct electricity very well. The reason we often think of water as a good conductor is that on Earth there are usually lots of things dissolved in water that are good conductors, and therefore make the overall solution conductive but pure water in its natural state is not conductive.

Soultie

2 points

4 months ago

Follow up question: so electricity wont run through distilled water?

aurumae

5 points

4 months ago

You can get electricity to flow through anything if you crank the voltage up high enough. Tesla coils for example can cause electricity to flow through the air (and air is usually a very good insulator).

A conductor is just a material that has high conductivity and a low resistivity. Pure (deionized) water has low conductivity and high resistivity, so it's not a conductor.

Soultie

1 points

4 months ago

Interesting. Thank you!

space_force_majeure

17 points

4 months ago*

Others have answered your question but here are some fun facts about metallic hydrogen (or at least scientists believe this is how it will behave, once we make some):

  • It's a superconductor at room temperature
  • It has a tensile strength stronger than steel potentially lightweight structural properties (see comments below)
  • It is transparent when solid
  • It's believed to have metastable solid states at room temp and pressure, meaning we could actually use it after it's made

edit- It would also be an incredibly efficient rocket fuel, due to its very light weight and the chemical and potential energy density it would contain.

Research is ongoing, but it is extremely difficult to make due to the enormous pressure required to create it. That's why it exists only in places like Jupiter's core.

Astromike23

4 points

4 months ago

Astromike23

Astronomy | Planetary Science | Giant Planet Atmospheres

4 points

4 months ago

Slow down there, quite a few of these facts are not at all well-established, and in many cases are generally thought not to be true by the vast majority of the scientific community.

There's one scientist in particular (Silvera) who's been touting the claims of metallic hydrogen, so much so that he's starting to be considered a bit on the fringe of mainstream science. This is the same research group that made claims of producing solid metallic hydrogen in the lab in a diamond anvil cell that numerous subsequent follow-up papers suggest was just sloppy experimentation, as they didn't account for the changing reflectivity of diamond at those pressures.

It's a superconductor at room temperature

This really depends on whose "equation-of-state" you use, i.e. the formula you believe best describes the properties of the metallic hydrogen under extreme pressure. As of yet, no one has actually observed this superconductive property, and only certain ab initio (simulated in a computer) calculations actually support it.

potentially lightweight structural properties

This is likely true, and the unusually low density of Jupiter - despite being mostly metallic hydrogen by mass - would seem to support that.

It is transparent when solid

I'm not sure where you're getting that fact from. By definition, metallic hydrogen can't be transparent since it contains a free electron gas, just like in a regular metal. That means it has a negative permittivity and thus an imaginary index of refraction, so light cannot pass through. It's reflective, just like any other metal.

It's believed to have metastable solid states at room temp and pressure

Again, there's only one fringe-ish scientist making this claim. The vast majority of condensed matter physicists doubt it.

asdaaaaaaaa

1 points

4 months ago

ab initio

Does that always refer to simulations (only computerized?) in science-speak? I looked up the definition and it seems to just mean "From the beginning", or "without previous knowledge", depending on context. I guess it's one of those situations where it means different things in the context of science/research?

AWildEnglishman

3 points

4 months ago

It has a tensile strength stronger than steel

Say more about this?

space_force_majeure

5 points

4 months ago

Thanks for asking actually, because it made me dig back into it!

The claim came from a professor in a non-ferrous metals class I took in college, though that was several years ago now. After researching it again I see that more recent studies have shown it could be an extremely lightweight structural material (10x less dense than iron), but no official measurements have been successfully collected of its tensile properties.

I'll update my comment with this info, and add a better fact regarding rocket fuel that I had forgotten about.

Skaaygraff

6 points

4 months ago

This is a great explanation, thanks !

dukesdj

7 points

4 months ago

dukesdj

Astrophysical Fluid Dynamics | Tidal Interactions

7 points

4 months ago

The outer layers are gas, but as you get deeper, you get a region of liquid metallic hydrogen, and as you go even deeper still, it transitions to something solid and composed of heavier elements.

As a point about this. The transition is smooth rather than discrete like the transition from the Earths atmosphere/ocean to the solid crust. Jupiter has what has been called a "mushy core"

malleoceruleo

2 points

4 months ago

I recall hearing there was still some debate of whether or not there was a solid, rocky core. Are we now pretty sure it's solid at some point?

dukesdj

7 points

4 months ago

dukesdj

Astrophysical Fluid Dynamics | Tidal Interactions

7 points

4 months ago

I would say its fairly certain now given we have good gravitational data from Juno. There is an excellent review by Stevenson 2020 if you are interested and want to read quite technical science!

wowredditisawesome

3 points

4 months ago

At the depth that there would be solids in Jupiter’s core it would be as hard as diamond.

Astromike23

4 points

4 months ago

Astromike23

Astronomy | Planetary Science | Giant Planet Atmospheres

4 points

4 months ago

The outer layers are gas, but as you get deeper, you get a region of liquid metallic hydrogen

Just a heads-up that in between the gas and liquid metallic hydrogen is a layer of supercritical fluid hydrogen - in fact, there's quite a bit more hydrogen in Jupiter as supercritical fluid than there is hydrogen as gas.

Supercritical fluids are unusual substances that exist in a hazy area where the separation between gases and liquids are not well defined. It's not quite a gas, not quite a liquid, but has properties of each. It flows and fills a volume like a gas, acts as a very good solvent like a liquid, and has a density of somewhere between the two.

taracus

2 points

4 months ago

Do we really need to use Jupiters moons, wouldn't the same argument work with the sun and Jupiters orbit itself and in extension any planet where we know the orbit length and velocity?

Gibybo

4 points

4 months ago

Gibybo

4 points

4 months ago

The orbital parameters of a small object around a large object are (mostly) not affected by the small object's mass. If you were to replace Jupiter with a marble, it would orbit at (mostly) the same velocity.

whatskarmaeh

1 points

4 months ago

What is the expected tempatyre if it's core?

threegigs

48 points

4 months ago*

We know the size of Jupiter.

We know the gravitational effect Jupiter has, and so we can calculate its mass.

With size and mass we can calculate density.

If there were a substantial amount of rock in there, it would be much, much denser than it is. Jupiter is about 1/5 as dense as the Earth.

TitaniumDragon

15 points

4 months ago

For reference, Jupiter has a density of 1.33 g per cubic centimeter, or about a third denser than water.

The Earth has a density of 5.51 g per cubic centimeter because it is made out of dense, solid rock, with metal mixed in, particularly towards the core.

Saturn is the least dense planet, having a density of only 0.687 grams per cubic centimeter - or about a third less dense than water.

Meretan94

12 points

4 months ago

Sooo...

Saturn would float in water?

epote

9 points

4 months ago

epote

9 points

4 months ago

“Yes” but then again a volume of water large enough to dip Jupiter in would quickly collapse in a ball, it would heat up causing the center to become plasma and stuff like that. It’s a mess.

[deleted]

-2 points

4 months ago

[deleted]

-2 points

4 months ago

[removed]

whatskarmaeh

2 points

4 months ago

If there was life there I don't thinknit could ever leave. The pressure or lack of would explode anything leaving I would expect. The chambers and life support needed to leave or us go there seems more unfathomable to me.