Have you ever looked at the wikipedia page of a Gas giant and thought:
“Man, I wish I knew this much about my fictional gas giant planet!”
Why am I even asking?
Of course you have, let's do this!
Youtube! Edgar here. And welcome to Artifexian.
Here you will learn everything you ever wanted to know about worldbuilding...
And then some!
The mass range of gas giant is 10 earth masses to 13 jupiter masses.
Simple! Radius however is a little more nuanced.
Between 2 and 13 jupiter masses a body will always be 1 jupiter radius in size.
Larger radii only occur below 2 jupiter masses.
This is kinda counterintuitive; you can thank electron degeneracy for that.
All things considers let's build.
First up let's construct a “Super Jupiter”
I.e a giant Planet more massive than jupiter.
Again we use the planet maker equation. G = M/R^2 = R(P).
Seeing as we are dealing with a super jupiter,
I'm going to pick, say, 3 jupiter masses.
Now, given that its above the 2 jupiter mass limit,
It must have a radius of 1 jupiter radii.
But for the sake of avoiding mathematical mundanity,
I'll allow myself to go plus or minus a few percent.
'Cause you know who likes boring maths; Nobody, that's who!
1.03 jupiter radii should do the trick.
Solving for gravity and density yields the following stats.
Remember all values here are relative to the jupiter = 1,
And to convert them to absolute values just multiply by jupiter’s absolute values.
Here's Jupiter and earth and here, to scale, is our super jupiter.
Same radius, seriously more massive.
And now for something completely different.
Lets build a puffy giant: i.e a planet below 2 jupiter masses but with a radius larger
Than jupiter.
I'll set my mass at 0.48 and my radius at 1.9, say.
Again plug the values into the planet maker, solve for gravity and density and you get
the
Following results.
Now these figures may seem a bit crazy
But they are in fact the stats of the exoplanet WASP-17b,
Proof that real life puffy giants are truly bonkers in nature!
I mean if we multiply that density value by Jupiter's absolute density we see that this
World has a density of 0.09 g/cm^3...
That's a whopping 7.5 times less dense that saturn!!
If that doesn't initiate cranial mind blow you should serious consider running a level
1
Diagnostic to see why you are not functioning within established parameters.
Digression aside, it's worth noting that the least dense exoplanet discovered to date has
a density of 0.03 g/cm^3
And the planet with the largest radius is in fact WASP 17-b at 1.9 jupiter radii.
Consider these a couple of figures to bare in mind when constructing your worlds.
Again here's jupiter and earth and here is our puffy planet.
Finally let's build a gas dwarf
I.e a gaseous planet smaller that Uranus and Neptune.
These planets break all the above parameters as they are transitional worlds blurring the
Line between gas planet, ocean planet and rocky planet.
Conservatively speaking a gas dwarf will be no smaller than two earth radii and could
have
A mass anywhere between 1 – 20 earth masses.
As explained in a previous video this means the gas giant will likely follow a generic
Mass radius relationship so we can use this graph to get realistic mass and radius values.
Here's the 2 radius line so everything below that is out.
Below 1 and above 20 earth mass range is also out.
And seeing as a gas dwarf will obviously be composed of gas everything here: Gone!.
Links by the way in the dooblydoo.
Okay so let’s go with say 2 earth masses and 4 earth radii.
Plug the values in to the planet maker and huzzah!
We get the these stats.
Bare in mind we are now talking in terms of the earth = 1.
For the final time.
We got jupiter and earth and here is our gas dwarf.
So thats how to build the various types of giant planet.
Remember you can help flesh out your world by calculating escape velocity, surface area,
Circumference and volume just as we did in the previous video.
Finally, a warning!
Not all types of gaseous planet can be placed wherever you want in your planetary system.
In order of increasing distance from their host star we are likely to find puffy planets
here,
Gas giants and super jupiters here
And gas dwarves here.
But more on that when we discuss orbits in a later video.