Have you ever looked at the Wikipedia page of a dwarf planet and thought:
"Man, I wish I knew this much about my fictional dwarf 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 world building...
and then some!
The most important variables to consider when building
any planet, dwarf or not, are radius, mass
surface gravity and density. To know these physical parameters is to know one's
planet.
Luckily, one very simple yet extremely important world building equation
governs all four values:
Gravity is equal to mass over the radius squared
which is equal to the radius times density. By the way, all values in this
video, unless otherwise stated, are relative to the
earth being equal to 1. Now, before we go throwing numbers at this equation
let's talk ranges for second.
The mass range for dwarf planets is 0.0001
to 0.1 Earth masses and their radii should be greater than 0.03
Earth radii. The values for density and surface gravity are more flexible and we can let
the equation determined them. Additionally, these ranges are not
fixed. Think the more as guidelines, so feel free to fudge the details either way if
you need to.
Just don't go crazy. Got it? Cool. Let's build. Here's my little dwarf planet:
Peter! Less give him a mass of 0.0002 earth masses,
and a radius of 0.084. After a bit of number crunching, Peter turns out to have a
surface gravity 0.028 times that of earths
and a density of 0.3. And this is great!
But what does it all mean? They're just figures, right?
Well, not really. The figures help tell the story of our dwarf planet.
Peter's low mass indicates he is barely massive to be in hydrostatic equilibrium,
and his low density indicates that he is primarily composed of ices.
His radius is only 8.4% that of earths,
and his surface gravity?: 3 percent! So in essence what we've created here is a
tiny ice world
that lives on the edge blurring the lines between dwarf planet and small
solar system body
So, here's the earth. And the moon, and here's peter shown to scale.
Look at him, he so TINY and CUTE... Anyways, let's calculates some additional parameters:
Escape velocity perhaps. Escape velocity is the minimum speed
object has to travel to escape the planet's gravitational pull,
without further propulsion. Escape velocity is given by the square root of the
mass divided by the radius.
Again, remember your answers here will be relatively to the earths escape velocity being
equal to 1. Some more number crunching, and we get the value of 0.05
which we can then multiply by the absolute value of the escape velocity on
earth...and BOOM! Turns out to escape Peter's gravitational pull we need to be
traveling at 0.56 km/s
So I think now's a good time to take all our previous
values a multiply them by their respective values on earth.
Which will give us a nice set of absolute values. From here we could take
absolute value of our planet's radius and use the basic geometry we all learnt in
school...and haven't forgotten!
To figure out Peter's circumference, surface area and volume
In this case 2 pi times the radius gives us a circumference of about 3,300 km
4 pi times the radius squared gives us a surface area of about 3.5
million square kilometres,
and finally 4/3 pi times the radius cubed give us a volume
just over 600 million cubic kilometers!
But Peter's feeling kinda lonely, let's give him companion because we care
deeply about him
and also because we want to try out different variables and see what
consequences are.
Same questions and ranges as before. Let's go with something a little more
massive say 0.0013 earth masses.
Similarly, let's choose a higher density of, say, 0.5.
One intense abacus session later and we see the Petra is a dwarf planet with the
following stats.
With values relative to earth being here and absolute values being
there! Again the story the figures tell is of a radically different planet.
Petra is a bit of a bruiser:
roughly as large and as massive as Jupiter is moon Io,
and as dense as Eris. A true heavyweight, rocky dwarf planet!
Once more, here's earth. Here's the moon and here's Peter and Petra.
I think they make quite the couple have cosmic cubeballs. Proof that opposites
attract, eh?
And, in part the difference it in the densities. a low-density world will be
composed
of ices. Intermediate density dwarf planets will be composed of a mixture of ice and rock,
and high densities with indicate a predominately rocky composition.
Unfortunately, it's difficult to give a nice neat set to have values on the density
ranges for dwarf planets.
I would advocate that when you finish building a planet always cross reference your results.
with the stats in this wikipedia page. Links in the dooblydoo,
just so we know exactly what we're dealing with.
With that in mind, go forth and build and let me know what stories your figure tell,
down in the comments.
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Thank you all so much for watching...Edgar out!