How‐to: Design a basic solar system

This brief tutorial is meant to guide you through the basic steps of a very common task in sci‐fi worldbuilding: Creating a solar system. In this example we will design a small and rather compact solar system around a K0 type star containing the following additional bodies:

1. A scorchingly hot rocky planet;
2. a “moist greenhouse” world with a pronounced greenhouse effect near the inner limit of the habitable zone;
3. a large gas giant with a sort-of habitable moon that has a CO₂ atmosphere;
4. a single gas giant far beyond the circumstellar habitable zone; and
5. a frigid ice planet far out.

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Step 1: Creating the star

On the Star sheet, navigate to the “Star properties” calculator. Type in the following values for a K0 type main sequence star:

• Mass: 0.8
• Luminosity: 0.5

If you wish to, note down or screenshot the star’s generated basic data. You can use the “Star color” calculator on the same sheet if you need a precise RGB color for an artistic rendering (or similar) of the star.

Step 2: Creating the planets and moons

Next on are the planets; those require two steps each.

Placing the worlds

Navigate to the “Planetary habitability” calculator on the Planet sheet and provide the following values for the five planets and the habitable moon:

Body	Semi-major axis	Bond albedo	Atmospheric absorption
1st planet	0.1 AU	0.2	0
2nd planet	0.7 AU	0.35	1
3rd planet	0.85 AU	0.6	0
* 3rd planet’s moon	0.85 AU	0.3	1
4th planet	2 AU	0.5	0
5th planet	4.5 AU	0.75	0

Again, write down the calculated data, especially the thermal properties.

Fleshing them out

Scroll up to the “Physical properties” calculator. Input the values from the table for the five planets plus the habitable moon and jot down any results you need:

Body	Mass	Density
1st planet	0.06 m⊕	5.4 g/cm³
2nd planet	0.8 m⊕	5.2 g/cm³
3rd planet	300 m⊕	1.3 g/cm³
* 3rd planet’s moon	0.12 m⊕	3.9 g/cm³
4th planet	15 m⊕	1.3 g/cm³
5th planet	1.8E-05 m⊕	1.6 g/cm³

Those numbers are, by the way, loosely based on Mercury, Venus, Jupiter, Mars, Uranus and Enceladus.

Ignore the “density of satellite” field for now, although you might check back later for the third planet’s moon.

The making of a moon

Now comes some fun tweaking. Change to the Satellite sheet and scroll to the “Lunar habitability” calculator. Fill it in with the data you already have. I recommend 4.17 Gauss for the planet’s magnetic field, which is the value for Jupiter.

Next, feel free to tinker with the magnetic field and distance to planet in the “satellite properties” paragraph until you have the moon you want. Note down the final results too, of course.

For a bonus, scroll up to the “Satellite appearance” calculator and check out how Planet 3 and its moon look from each other. For the sunlight amount you can use the inverse-square law, in this case .

Step 3: Whirling everything around

Using the “Orbital properties” calculator on the Planet sheet you can then find out the most basic orbit data. Note that eccentric orbits and orbital resonances are not yet supported, but this calculator can give you a rough idea how things fit together.

Step 4: Go with the flow

Using the data you have worked out as a base, you may want to continue by doing more detailed and realistic calculations for the elements of the solar system, or simulating the entire system in a software such as Universe Sandbox.