J: Jupiter

What else would I be doing for J? :)

My science fiction universe, which I call the Jovian Frontier, took root around this giant planet for several reasons. One was the deep influence that the movie 2010 had on my young brain. (I blogged about that.) Another is the size and inherent challenges of the system. Jupiter seems to have an endless supply of moons, it's separated from the inner planets by the asteroid belt, and it's too far from the sun to even pretend to do any farming. It requires true independence from Earth's resources if you're going to set up a homestead here.

Jupiter itself was the fun part. It taught me some important things about getting around using real-world physics -- because I wanted this universe to be as hard-SF as possible. Let me try to explain one of those things by talking about some of Jupiter's moons.

The four biggest moons
Jupiter's four biggest moons are all found close to its equatorial plane -- they orbit more or less in line with the planet's equator. These are the moons you've probably heard of: Io, Europa, Ganymede and Callisto. They're a natural target for colonization (and fighting over) because they're large and relatively easy to get to because their orbits are nice, neat circles around the middle of the planet.

The prograde moons
Outside of the four biggest moons, there are six prograde (orbiting in the same direction Jupiter turns) moons. Four of them orbit at an angle of about thirty degrees relative to Jupiter's equatorial plane. The other two are off doing their own thing.

The retrograde moons
Outside of the six prograde moons, there's a wild array of retrograde (orbiting opposite to Jupiter's turning) moons. Most of them are less than 10 kilometers in diameter, and they're generally grouped by their angle of inclination relative to Jupiter's equatorial plane. These angles are numbers like 150, 165, and 140.

The "Seven Sisters" (as I call them)
The seven largest moons outside of the inner four are: Himalia, Lysithea, Elara, Carme, Ananke, Pasiphae, and Sinope. Leda gets an honorable mention. That's everything that's more than 10 kilometers across, outside of the inner four. The first three plus Leda are the prograde moons at a thirty degree angle that I mentioned. The others are large members of their similar-angle groups.

Why am I going on about angles?
Because traveling further than you have to, in space, is expensive. And dangerous.

All of the planets in our solar system orbit the sun within a fairly tight plane -- which is to say that when the planets "line up" there's one a little "higher," one a little "lower" but they're all fairly close to each other. Therefore all the places you want to travel to and from do not require angling yourself too dramatically away from everything else.

Which means, by extension, that when spaceships are coming and going from the entire Jupiter system, they're going to approach it along a fairly tight band of vectors that line up pretty well with its own equator.

Which means that the equatorial plane -- and the moons convenient to it -- are where the traffic is going to be. Where there's money to be made. It's also where the four biggest moons are, the ones that can give a ship the most help with slingshot acceleration or braking. (Free acceleration? Hell yes.)

The other moons can be expensive to get to, depending on where they are in their orbit -- you'll have to burn all the way out there and brake on your own. The seven sisters can help a little with that, but the rest of the dinky rocks are even worse.

This told me a few things about the Jupiter system: where the center of town is, where the boondocks are -- though even the boondocks get their turn close to the equatorial plane, it should be noted -- and the importance of location, location, location.

How does ease of travel (or difficulty) impact your story?