Let's Build a World! Part 2

Welcome back to my ongoing worldbuilding series! Last time I introduced the idea that I wanted to create a Pathfinder/Dungeons and Dragons campaign setting from scratch, and I spent a little time laying out some of the basic tenets that I will try to keep in mind during the design. Today, I want to move on into something concrete and discuss the physical world itself.

I’m an earth science, geology, and astronomy nerd (in fact if I could jump back to being in high school again and have a do-over on career path, my dream job would be something akin to an Exo-geologist). So I want to keep this grounded in science and realism. And that means that first of, our world, meaning the planet itself, is roughly Earth-sized, so that all the physics still make sense thanks to similar gravity.

Or is it? Gravity is a function of mass, not size, so even if the planet were a different size than the Earth, it could potentially still have the same gravitational pull if the overall planet density was different. Now we said last time that we want the planet to be mostly water, and water is less dense than rock and metal. But an ocean, even a large ocean, only goes so deep, and really won’t make up too large a percentage of a planet’s makeup.

So the density will come down to what the planet’s rocky structure is actually made of. To be Earth-like, it would have an Iron-Nickel core, and various heavy elements compacted around it. By tweaking this makeup, we could tweak the density of the planet.

I like the idea of the planet being smaller than earth (not to an extreme amount, we’re not making The Little Prince RPG here). A smaller world seems to fit the theme of scarcity I discussed last time. I want this world to have less ‘stuff’, so let’s make it smaller, which means there is less room for ‘stuff’. So we need to increase the density a bit to keep the gravity right, which means we need material within the planet that is more dense than iron and nickel.

So what do we put in there that makes sense? Well, the two heaviest natural elements are Iridium and Osmium, and they are both considered rare-earth elements. But they are found commonly in meteorites. So the idea is that our world has seen extra hits by iridium and osmium rich meteors, and happily enough that ties directly into another idea that I already had.

As mentioned previously, this world is going to be primarily water, with the land present mostly in the form of mountainous islands. What do we need to get islands to raise out of the ocean? Well, we can rely on plate tectonics to push them up slowly. We can rely on volcanoes to raise them up a little more quickly. Or, we can get upturned dry land instantly with a good old fashioned giant meteor strike.

So, at some point in the primordial past, our little world was struck by a very large, rare earth element laden asteroid. Said impact thrust the seabed upward in the form of an impact crater, and the higher peaks of this crater now jut above the waterline. Perhaps this major impact churned up the crust enough that the magma underneath has leaked upward, and scattered volcanoes added to the sudden land growth. But overall, our lands now take the shape of an impact crater...so what does that look like?

Courtesy of NASA, here's a picture of the Herschel Crater on Mimas, one of Saturn's moons. We have a ring of raised land, with a small upthrust in the center. So there we go. Our island chain will be a crescent shape, with perhaps one central small landmass. In a future post, we'll get to have the classic fun of actually drawing it out on graph paper!

Fantasy cartography! Is there anything more thrilling?

No. No there is not.

In my next post, I'll nail down some more physical details and start talking biology! Thanks for reading!