Random Planetary System
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Basic Information

This page generates random Planetary Systems and Star Systems, to aid with the creation of destinations in your Sci-Fi RPG.

Step 1: Star System

First you'll need to determine how many stars are in your system. In the majority of the cases, it's going to be one or two. Just over 50% of the stars that have been cataloged by science are binary star systems. Other data suggests that perhaps as many as 66% of the stars in the galaxy are solitary stars (most of them singular Red Dwarf stars). Regardless of which data you follow, trinary and other larger multiple star systems appear to be relatively rare.

  • One option would be rolling a d6, and caring mostly about whether it's odds or evens - on an odd result it's a single star, on an even result it's a binary system. On a "6" you instead roll again and the system has a number of stars equal to the number on the second roll.
  • Alternately, you could click on each of the three tabs below and decide which grouping sounds like the most fun.
  • As a last alternative, it may be easiest to always go with single stars unless given a reason to do otherwise. Many binary or multiple star systems are spread out enough that planets each orbit just one individual star, anyway. Note however that the single star tab feeds from a slightly different pool of stars than the other categories, so you might want to mix it up a bit from time to time.

If you desire, larger systems (like the Sextuple system of Castor (Star)) may be generated by using multiple tabs together, or by waiting a few moments and then hitting refresh.

The "solitary star" tab always generates a star that can support life and the formation of planets. The binary and trinary systems include some more exotic star types, so there's some possibility of non-habitable systems coming up, such as a binary system where the only star entries were two types of black hole.


Step 2: Planetary System

This section generates planets, or at least broad categories of planet. You will need to determine how many planets you're using. Most systems will only have a handful of planets that are actually worth the trouble of colonizing, however. Assuming your main PC race is humans, there's not much point in settling in a system that has nothing but flaming balls of rock. So, we'll assume there's at least one planet worth setting foot on.

Step 2a: Habitable Planets

Habitable planets may still require some level of Terraforming, or even the daily use of advanced technology to survive on the surface, but they at least don't melt or freeze your ship within a few hours of landing, and they have something to land on.

You might roll d4-1 to determine how many habitable planets are in the system, with a minimum value of 1.

Step 2b: Stick A Hat On It

There's a long-standing Sci-Fi tradition of summing up planets by just one or two details. Often this is phrased as "It's like earth, but…" or "Like earth, but with more…" Other times, planets are presented as being a single environment, or the people of the planet all have one cultural or personality trait in common. See Planet of Hats for more ideas. On some level it's a little silly, but if your game is going to hop from planet to planet from session to session, it's probably a useful abstraction to just boil every world down to one or two concepts. So, a couple of random links are provided here to help you pigeon-hole planets…

For a more nuanced and realistic depiction of a planet's cultures, you could use our Random Nation Generator. Sticking a hat on it is meant just to give you a quick concept or two to improvise around.


Step 3: Other Celestial Bodies

Step 3a: Uninhabitable Planets

These are planets that a quick scan suggests would be too difficult for humans to colonize. Starfish Aliens or Sufficiently Advanced Aliens might not have a problem with it. If there's some resource rare enough, or populations are exploding back home, people might figure out how to make do, but in general you're better off putting your energies elsewhere. As a rule of thumb, assume every system has 2d4 such uninhabitable planets.

Step 3b: Other Bodies and Hazards

This section includes planetoids, asteroids, anomalous readings, and other navigational hazards that might suggest encounters in your setting.


Step 4: Adding your own ideas to your creation.

Customize those results, and work out whatever details you'll need.

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