Stellar System Generator, Part 5

Copyright RMF Runyan © 2011

Edited by Aaron Smalley for The Guild Companion

"This leads me to think that if we never had a Jupiter, how many other planets our system might have contained. Makes one wonder If Saturn had been the Prime Jovian, we might have had a planet where the asteroids are now and perhaps another terrestrial type planet between it and Saturn. We shall never know"

Editor's Note: The following is the final chapter (Chapter 5) and the Appendices of the documentation provided by the author. This as well as the previous four installments are intended to provide background information as to the science and reasoning behind the application that RMF Runyan has put together. RMF Runyan has shelved working on the version of the program that had been appearing linked from the "Users Guide", however he has changed directions and is instead working on a web-based version located at the following url: http://www.conceptvisions.net84.net/SSG/index.html .

Chapter 5: Moons

Almost every planet has satellites of one form or another. Even in our system has 6 of the 8 planets with satellites. Even some Kuiper Belt Objects have satellites, such as Haumea andEris. There is even an asteroid with a satellite: Ida with satellite Dactyl. These only suggest that objects with satellites may be the norm, instead of the exception.

Tidal Forces

Perhaps the most important effect a fairly large moon can have on a terrestrial planet is its stabilization effect of the planet's axial tilt (obliquity to the ecliptic, a.k.a. Orbital Obliquity). With a large enough moon, the moon's gravitational tidal forces can override the effects from other planets in the system. Without our Moon, Earth's axial tilt would wobble wildly from time to time. In as little as a few millennia, the tidal tugs from other planets could tilt a planet from no tilt to a tilt over onto its side, or even upside down like Venus, causing extreme seasonal changes. Such catastrophic events would not be very conducive for the development of complex life. With a stable axial tilt, complex life can develop and adapt to and take advantage of the seasonal changes (if any).

With the development of oceans and the tidal effects on those oceans, tidal pools and estuaries can form which can serve to help life make the gradual transition from marine to terrestrial life.

Tidal forces are the result of the fact that gravitational attraction drops off with distance. The nearest point of a moon will be pulled more strongly than the farther point of the moon. This has the effect of stretching the moon slightly. If the moon orbits or rotates fast enough, this stretching effect can give the moon a molten core as the forces stretch and relax the moon's shape. A very good example of this is Jupiter's moon Io. Io is the most seismically and volcanically active object in our system, even more so than our Earth. Europa is another good example as the tidal forces help heat the water under its icy crust to create surface regions of slushy ice which help to resurface Europa, erasing evidence of any impact events. Also, the thin icy crust can allow impactors to penetrate deep enough to be back-filled, and thus erased.

Tidal forces are like a double-edged sword, they cut (effect) both ways. In its ancient past, when the Moon was much closer to the Earth, its tidal force was enough to pull the land up to 80 meters higher when it was overhead. Now, the Moon is too far away to affect the rigid crust, but it does affect the liquid oceans. It is the tug of the Moon and the friction between the oceans and crust that is helping to slow the Earth's rotation. Eventually, in another billion years or so, the Earth's rotation will slow enough that the Moon will only be visible from one side of the Earth. Yes, the Earth and Moon will eventually tidally lock with each other and become a double planet system instead of its current planet-moon system.

The Roche Limit

The Roche Limit is the critical distance in which a moon may exist, or it gets torn apart forming rings. Gravitational tidal forces from the planet will simply tear apart any moon that may wander within this limit. Also, note that the Roche Limit is measured from the planet's center, not the surface. Although density is a variable, it works out to a distance equal to the planet's radius ×2.446. For example, the Roche Limit for Earth equals 15,600,833 meters; or 9,222,733 meters above the equatorial surface. Inside this limit, only rings can exist. Outside, moons. If you know the radius and density of the planet and the density of the moon, you can calculate the exact distance the moon may be before it is torn apart from the planet's gravitational tidal forces by using the below equation.

\[ D = R \left(\frac{2 \rho_M}{\rho_m}\right)^{\frac{1}{3}} \]

Where \(D\) = Roche Limit; \(R\) = radius of primary object; \(\rho_M\) = density of primary object; \(\rho_m\) = density of secondary object.

Note: Units for Roche Limit are dependent upon units used for radius. If you use meters for radius, Roche Limit will be in meters. The units for both densities MUST be the same (standard = kg/m3).

Hill Sphere, Hill Radius

Sometimes called the Hill Radius, and more rarely the Hill Limit, the Hill Sphere is the limit in which a moon may remain as a stable satellite before it is pulled away by the star into its own stable orbit about the star. Although the mathematics for determining this radius is fairly brutal, I have found a simplified equation that is still fairly accurate, depending upon orbital eccentricity. If the planet's orbital eccentricity is less than 0.05, then the below equation will have an error margin about ±0.02104%. Greater orbital eccentricity will mean an even greater chance the moon will be pulled away to become a stable orbital path itself. Orbital eccentricities less than 0.00001 can be ignored (use the second equation).

\[ R = a(1-e)\sqrt[3]{\frac{m}{3M}} \] \[ R = a\sqrt[3]{\frac{m}{3M}} \]

Where \(R\) = Hill Radius; \(a\) = mean orbital radius (planet); \(e\) = orbital eccentricity (planet); \(m\) = mass of the smaller object (planet); \(M\) = mass of the heavier object (star).

Notes: The unit for Hill Radius will be dependent on the unit used for the mean orbital radius (MOR). If you use kilometers for the MOR, then the Hill Radius will be in kilometers. The units for both masses MUST be the same (standard = kilograms).

HillSphere.png
Diagram Showing Contour Plots of the Effective Potential of a Two-Body System
Due to Gravity and Inertia at One Point in Time and Showing the Five Lagrange Points and Hill Radii

In the above image, the complete circular (not necessarily true circles) contours around the planet are the safe orbits for a moon about a planet and the other ones are where another planets could safely orbit (or moon pulled away from the planet. Please note as the caption states, this is for one moment in time. The contours will vary as the planet orbits the sun due to orbital eccentricity and perturbations from the moon and other planets. Thus the above equation is only good for that single point in time. However, where eccentricities and perturbations are very miniscule, the above equation will be fairly accurate for all points of time, barring some nemesis-like event (see Nemesis Events).

Rings

Rings are related to moons and may be formed in the same processes, or formed later from a moon falling within the planet's Roche Limit. Rings lie within the Roche Limit and can extend all the way down to low orbit (maximum of one-third of Roche Limit). Rings may be complex, like Saturn's, or gossamer, like Jupiter's. Using the example for Earth above, rings may exist within 9,222,733 meters to 4,022,455 meters above Earth's equatorial surface.

Generating Moons

For planets in the Epistellar Orbits, do not bother generating moons since they cannot survive for very long. The star would pull them in and consume them within a million years, or two. As a general rule-of-thumb, the closest orbit that may have a planet that may have a satellite is 0.5 AUs (modified by multiplying the star's mass in Sol units). Another general rule-of-thumb for terrestrial type planets is the total mass of satellites cannot exceed the terrestrial planet's mass ×0.25. This is the maximum for a planet-moon system. Satellites may come about for several reasons.

· Formed along with the planet in the protoplanetary disk.

  • Was later captured.
  • Formed due to a giant impact.

· Formed as part of a double planet and later gravitated outwards.

  • Many other reasons yet to be discovered.

Moons can come from a variety of sources, and astronomers still do not completely understand what goes into the formation of planet-moon systems. It is known that most moons are most likely captured later from bits of protoplanetary flotsam. Deimos and Phobos are examples of captured moons. The Earth-Moon system is perhaps an example of the Giant Impact Hypothesis.

Number of Moons

For the purposes of the SSG, it refers to moons of planetoid size or larger, >= 800 kilometers. Moons smaller than this are not generated by the SSG, and they are considered asteroidal. Jovian type planets can play host to literally dozens of moons, if not hundreds. This SSG only generates the major moons. If you wish to spend the time cataloguing each and every little rock that orbits a Jovian, then do so. I shall not stop you, as if I could. If you desire a tiny asteroidal moon, a ring-arc, shepherd moons, etc., then feel free to indulge yourself. Eliminating the lesser moons makes the generation of moon systems much simpler. Real world examples using this SSG are listed below.

Earth (pelagic) 1 lunan

Jupiter (Prime Jovian) 1 lunan, 2 glacial, 1 planetoid/glacial (Europa)

Saturn (cryojovian) 1 glacian, 4 planetoids

Uranus (cryosubjovian) 4 planetoids

Neptune (cryosubjovian) 1 planetoid

Terrestrial Jovian
01-75 1 01-25 d4
76-90 2 26-50 d6
91-98 3 51-75 d8
99 4 76-95 d10
00 5 96-00 d12

Remember, only major moons are generated.

Moon Orbits

This can be tricky. However, I have simplified it. Or, I should say that I decided to create the easiest method I could figure out. Simply roll 3d5, multiplying each roll (d5 × d5 × d5). The resulting number is the number of planet diameters the moon orbits. See the below image for a visual representation.

Moon's Orbit if Result Rolled is 6

For Jovians, if the result is 1 or 2, then it indicates rings. For terrestrials, if the result is 1, roll d100; 01-10 = rings, otherwise reroll for orbit.

Please remember that you may choose. Again, as aforementioned, do not enslave yourself to the dice!

You can calculate the orbital period of each moon using the same equation to determine a planet's orbital period. However, the planet's mass, not the star's, is the central body. As with the planet's orbital period, the result will be in total seconds.

\[ T = 2\pi\sqrt{\frac{r^3}{G(M+m)}} \]

Where \(T\) = total time in seconds; \(r\) = mean orbital radius in meters; \(G\) = Gravitational Constant (6.67428e-11 m3/kg-s2); \(M\) = mass of planet in kilograms; \(m\) = mass of moon in kilograms.

Also, if you want the moon to have a certain orbital period about the planet, you can use the below equation to calculate its orbital radius. And you could treat that moon as the Foundation Planet (Moon) for determining the other moons.

\[ R = \sqrt[3]{\frac{T^2 G (M+m)}{4\pi^2}} \]

Where \(R\) = mean orbital radius in meters; \(T\) = orbital period in seconds; \(G\) = Gravitational Constant (6.67428e-11 m3/kg s2); \(M\) = mass of planet in kilograms; \(m\) = mass of moon in kilograms.

Types of Moons and Mass

Most often, moons will be lunan, glacial, or terran in nature. Around Jovians, the only time there will be a pelagic or oceanic type will be if the Jovian orbits the star in the Inner System orbits. Glacial type moons will only exist in the outer half of the stellar system. Occasionally, a pelagic type moon can exist due to tidal forces heating its interior. If they are in the outer half of the stellar system, these pelagics will be like Saturn's moon Titan, having oceans of methane and/or ethane instead of water. Use logical reasoning and choose the type of moon, or you can use the below table.

01-50 Planetoid Moon 0.001 to 0.01 Me
51-85 Lunan/Glacial 0.005 to 0.05 Me
86-95 Terran/Glacial 0.05 to 0.1 Me
95-00 Pelagic/Glacial 0.1 to 0.75 Me

-10 for terrestrial type planets; +10 for Jovian type planets

1 Me = 0.003 Mj and 1 Mj = 0.00095 Ms

One-Ten Thousandth Rule

This rule only applies to Jovian type planets. As a Jovian type planet forms, it begins to become massive enough that its gravity becomes very hungry, pulling in ever increasing amounts of matter. The Jovian will become hungry enough that only about 1/10,000th (0.0001) of its mass will be left for moons. I know, if you total the mass of the moons about Jupiter, Saturn, and Neptune, their total mass is more than 0.0001× that of the host planet. This is due to capture events later on. Jupiter more than likely captured Io, Europa, and Ganymede. Callisto may have formed as a moon and was later pushed outwards as the other three were captured. In all likelihood, Titan was captured by Saturn, and Triton was captured by Neptune. Uranus has far less moon mass than expected, probably due to the cataclysmic event that tilted it on its side (~98° axial tilt).

Thus, when generating moons for Jovian type planets, you need to keep this rule in mind. You may distribute this mass amongst the generated moons as desired. Or you may roll for the mass randomly using the Terrestrial Mass tables on pages 52-53. However, when all available mass is "taken," any remaining moons are considered to be planetoids. In Case of Emergency, when you just must have that extra lunan or glacial moon, allow maximum extra 0.01 Me.

Moons of greater than the recommended maximum mass are still possible. Most of the time this will be the case since the Jovians can more easily capture moons at a later time. In such a case, you may allow an additional 1/10,000th mass for a total of 1/5000th. For Superjovians, you could allow an extra 1/10,000th mass for a total of 1/2500th. For Hyperjovians, you could allow an extra 1/10,000th mass for a total of 1/1250th.

Rings

I have simplified ring determination. If you did not get any rings in generating Moon Orbits above, then use the tables below. As always, you can just simply to choose to have rings.

01-50 No rings 01-75 Gossamer
51-00 Rings 76-00 Complex

Note: For terrestrials, add -20; for Jovians, add +20.

If desired, for ring complexity, you can simply roll d100, reading 00 as zero, to get a number 00-99. Higher numbers towards 99 would indicate more complex ring structures.

Appendix

Apparent Magnitude

This equation is only used to determine the star's magnitude when it is viewed from another stellar system, or other location. First, you will have to calculate the distance. I cannot help much with this since I have no idea where the stars are located in reference to each other. However, you can use the 3‑D Pythagorean Theorem as long as you know the x, y, and z coordinates of the stars.

\[ d = \sqrt{(x_1 - x_2)^2 + (y_1 - y_2)^2 + (z_1 - z_2)^2} \]

The zip package this document came with has an app to do this calculation for you: 3DPy. If you use light years as the units in this app, you can also calculate distance in parsecs.

Use the below equation to calculate the apparent magnitude.

\[ m = M + 5 \log \frac{d}{C} \]

Where \(m\) = apparent magnitude; \(M\) = absolute magnitude; \(d\) = distance from observer; and

\(C\) = 10 if d is in parsecs

\(C\) = 32.6168807 if d is in light years

\(C\) = 206,265.325157 if d is in AUs

\(C\) = 30,857,292,643,553.7542 if d is in kilometers.

Relative Brightness Difference: This will give you relative difference in brightness between two luminous objects if the absolute or apparent magnitude is known. The magnitude must the same type for both objects, whether apparent or absolute.

\[ \Delta B = 2.512^{\Delta m} \]

Where \(\Delta B\) = relative brightness difference; \(\Delta m\) = difference in magnitude rating; must be the same magnitude, absolute or apparent.

Angular Diameter

Ever wanted to know how big an object appears in the sky? This is called the angular diameter, the angle the diameter of an object covers in the sky. To calculate this, you need to know the diameter of the object, and how far away the object is. The equation below works for any object, whether it is a star, planet, asteroid, moon, etc. Please note that the equation below is simplified and automatically converts to decimal degrees. The equation in the Wikipedia article gives the angular measure in radians.

\[ \alpha = \frac{D}{a} \times \frac{180}{\pi} \]

Where \(\alpha\) = angular diameter in decimal degrees; \(D\) = diameter of observed object; \(a\) = distance between observer and object.

Note: The units for diameter and distance must be the same.

The Wikipedia article linked above also lists some angular diameters, but it lists them in DMS (degrees, minutes, seconds). Some calculators have a DMS to DD conversion button. If you don't have one, then see below.

Converting DD to DMS

There are two methods for recording angular measure: DD (decimal degrees) and DMS (degrees, minutes, seconds).

1. Remove the number to the left of the decimal point. This is the number of degrees.

2. Multiply the remaining decimal by 60. Remove the number to the left of the decimal. This is the number of minutes.

3. Multiply the remaining decimal by 60. Leave this alone. This is the number of seconds.

Say we have an angular measure of 0.533 degrees. We have 0 degrees. Multiplying by 60 gives us 31.98 minutes. Now multiplying 0.98 by 60 gives us 58.8 seconds.

The result can be written two ways: 0d 31m 58.8s OR 0° 31′ 58.8″.

Creating Your Own Time Units

Please note that I do not go into extensive detail in this section. I write it hoping you have a general understanding of some basic math concepts.

Since you have already calculated you focus world's orbital period in total seconds, we can actually create our own time units. The simplest method is to take the total number of seconds and factor it down. The first six prime factors are: 2, 3, 5, 7, 11, and 13. You should not need a prime factor above 13. Just for comparison, an Earth Standard Year equals 31,557,600 seconds. Try and break this down into primes. You will end up with an ugly prime of 487. Nasty. But, I am not going into details about our world…

We will use the original orbital period for Onaviu for an example of what not to do. Onaviu's original orbital period was 146,313,216 seconds. It factors down to 212 × 36 × 72. The biggest problem with this is there is no way make to make minutes and hours equal to 60 units. We need at least two 5s to do so (60 factors down to 22 × 31 × 51). Let's see what we can do.

First, I'll try to get a minute as close as possible to 60 units. The best we can do is 56 or 64 (23 × 7 = 56; 26 = 64). Since we are talking about another world, why would they use the same kind of time units? I decided to make a minute = 56 seconds and an hour = 64 minutes.

That leaves us with 23 × 36 × 71. Let's see if we can get 24 hours. 24 factors down to 23 × 31. How about that? We can make the day 24 hours.

That leaves us with 35 × 71. This leaves us with total days in a local year, which is 1701. Whoa! Now that is a long year! But I already knew it would since Onaviu year = 146,313,216 seconds. That is 4.636386 times longer than an Earth year. Of course you could use those remaining numbers to devise weeks and months.

However, I felt the above system would be too confusing to use in a role playing setting. Thus, I went back and totally restructured the entire stellar system to get a workable system. (I will be writing an appendix article on how to do this.) After redesigning the system, I got Onaviu's orbital period at 49,766,400. It is still longer than an Earth year, but more acceptable than previous, since it factors down to 213 × 35 × 52.

This allows me to make minutes and hours equal to 60 units. Thus, we have a minute = 60 seconds, and an hour = 60 minutes. I could also make a day = 24 hours. However, I already determined that Onaviu's rotational period = 115,200 seconds or 32 hours. Since 32 factors down to 25, that will leave us with four 2s and three 3s.

This leaves us with 24 × 33 = 432. That's fine. We can use it to make a year = 432 local days. In Earth time, an Onaviu year is 576 Earth days or 1.577 Earth years.

You can create your own time units by simply determining all the prime factors of the total seconds of a length of time and combining them as desired. Just remember, when combining the factors, they are multiplied, not added.

Standards and Measures

Sol Mass 1.98892e30 kg Gravitational Constant 6.67428e-11 m3/kg-s2
Sol Radius 6.955e8 m Boltzmann Constant 1.3806504e-23 J/K
Sol Luminosity 3.839e26 J Stefan - Boltzmann Constant 5.6704e-8 W/m2k4
Earth Standard Gravity (g) 980.665 cm/s2 Light Speed (c) 299,792,458 m/s
Earth Standard Year 31,557,600 s Light Year (ly) 9,460,730,472,580,800 m
Earth Standard Atmosphere 1013 mb 760 mmHg Parsec (pc) 3.261688071 ly
Earth Mass 5.9736e24 kg Astronomical Unit (AU) 149,597,870,691 m
Jupiter Mass 1.8986e27 kg

Determining Orbits Using Your World as the Foundation Planet

This can seem complicated, but is actually fairly easy. Say you want a world to have a year that is 37,324,800 seconds. To find the mean orbital radius, we simply algebraically rearrange the equation for orbital period to get the below equation.

\[ R = \sqrt[3]{\frac{T^2 G (M+m)}{4\pi^2}} \]

Where \(R\) = mean orbital radius in meters; \(T\) = orbital period in seconds; \(G\) = Gravitational Constant (6.67428e-11 m3/kg-s2); \(M\) = mass of central body in kilograms; \(m\) = mass of orbiting body (your planet) in kilograms.

Convert the result R into AUs by dividing the result by 149,597,870,691. Now that you have the mean orbital radius of your world, you can treat it as the Foundation Planet. Of course, this is going to restructure your system as previously generated. But that is OK. Even if your system has a Prime Jovian, it will get readjusted along with all the other orbital paths.

For planets inside the orbit of your world, begin with the next orbit inside and divide your world's orbit value by (1.3 + (d12÷10)). Record this value and use it as the basis for the next orbit inside and repeat until you have determined the orbit values for all planets inside the orbit of your world. If any planet's orbit ends up less than the 0.02 AU orbit, then disregard and move it outside the orbit of your world, or simply delete that orbital path. Please remember the 0.02 AU orbit may be of a different value modified by the star's mass.

For planets outside the orbit of your world, begin with the next orbit outside and multiply your world's orbit value by (1.3 + (d12÷10)). Record this value and use it as the basis for the next orbit outside and repeat until you have determined the orbit values for all planets outside the orbit of your world.

Transplanetary Region

In our stellar system, we call this zone the Kuiper Belt. This is a realm of pristine materials from the very beginnings of the system's formation. It lies beyond the orbit of the outermost planet and may extend another d12 + 16 AUs. It is a region mostly comprised of lumpy debris which is 50:50 rock and ice and is akin to an asteroid belt. It is from this region where most of the system's comets originate, especially the long-term comets that may take 3000 to 75,000 years to complete one orbit.

Some will only appear once on a hyperbolic orbit. Although most are small, some of the objects in this region can approach large planetoid status such as Pluto-Charon, Sedna,Makemake, andHaumea, and some can approach small planet size such as Eris. It is these larger transplanetary objects that can perturb smaller objects, sending some into the inner system. The transplanetary region can contain a huge amount of material. Our Kuiper Belt is believed to contain some thirty+ Earth-masses of rock and ice. This material is very widespread and rarely forms into objects larger than 0.25 Me. If the GM desires to have a glacial planet in this region, s/he should feel free to place one there.

Even further out is the Oort Cloud. This region is a hypothetical spheroidal cloud of comets which may lie up to a light year out from the star. This region is sparsely populated with small icy rocks, most being less than 200 km.

There is no table for random determination for planets, Plutoids, and planetoids for the Transplanetary Region. If you want such an object, just place it. Please note that no object will be greater than 0.25 Me. Also, its density will rarely exceed 2500 kg/m3, due to being mostly composed of ices.

Magnetism & Radiation

A planet's magnetic field is highly dependent upon the construction of the planet's core. Virtually all terrestrial type planets will have a nickel-iron core. Whether the core has a liquid, molten outer core and a solid inner core is the determining factor. If a planet's core has cooled to the point where it is completely solid, there will be no magnetic field generated. Or, it is very weak, too weak to protect the planet. To generate a magnetic field strong enough to protect a planet from the star's brutal emission of radiation, especially in the inner orbits zone, the outer core needs to be molten liquid metal and is dynamically convective in respect to the solid inner core.

Even if a terrestrial planet has a global magnetic field, it can fluctuate in its strength and orientation. Earth's magnetic field has exhibited several polar shifts in the past. This geomagnetic reversal was finally proven by seafloor magnetic striping. It is perhaps these geomagnetic reversals that help to create the evolutionary leaps that have occurred on the Earth. This reversal occurs on a period of every 300,000 to 800,000 years. The last occurrence happened about 780,000 years ago. (Perhaps Earth is overdue for a reversal?)

A planet's geomagnetic field greatly affects the amount of radiation received on the planet's surface and the space around it. Geomagnetic fields can deflect and trap charged particles from the stellar particle winds creating highly radioactive toroidal fields about the planet like the Van Allen Belts around the Earth. These belts are very dangerous to both spacecraft and living beings without some form of shielding. However, by trapping these charged particles, the geomagnetic field keeps them away from the planet and creates a protective field so life may exist.

Jovian planets similar to Jupiter can generate incredibly powerful magnetic fields. Jupiter's is even more powerful than the magnetic field generated by a MRI scanner. The frontal bow shock wave of Jupiter's magnetic field is approximately 82 Jupiter radii above Jupiter's surface (5,732,702 km). In comparison, Sol's radius is only 695,500 kilometers. The radiation belts about Jupiter are capable of killing a human within minutes (estimated to be about 3 to 4 minutes).

Planets without protection from a geomagnetic field are virtually defenseless from the charged particle winds of their star, and the radiation level on the planet's surface will match that of the local region of space around the planet. The presence of an atmosphere can mitigate the surface radiation somewhat. However, it will not protect against stellar flares and coronal mass ejections. A heavy, thick atmosphere (like Venus) can provide complete protection, generating their own magnetic field from the interaction of the atmosphere with the charged stellar particle winds, helping to prevent the atmosphere from being lost.

Planets with weak or surface-localized magnetic fields have another problem dealing with solar radiation and stellar winds. The charged particles are not stopped and bombard the atmosphere directly.

Low gravity planets (<= 0.35 Me) will have their atmosphere stripped away in a matter of a few million years to a few hundreds of millions of years. This atmosphere stripping will also ionize water into hydrogen and oxygen gases which will in turn be stripped away. This is what happened to Mars.

On heavier planets (0.4 to 1.25 Me), the charged stellar particles are absorbed by the atmosphere, again causing water to ionize into hydrogen and oxygen. Since hydrogen is so light, it is lost into space as the stellar winds strips it from the atmosphere. The oxygen will usually combine with other substances such as carbon and sulfur, forming heavier gases. The planet is able to hold onto heavier gases, creating a thick, toxic atmosphere. This is what happened to Venus.

The above two examples show the importance of a planet having a protective geomagnetic field. Without such protection, no planet could harbor complex surface life. Planetary magnetic fields (PMF) can be broken down into six groups.

PMF1: Weak, localized

This type of field is similar to those of the Moon and Mars. Basically, there is no global field. However, there may be small concentrations of polarity scattered at random across the surface. The strength of the field is less than or equal to 0.01 gauss.

PMF2: Weak, global

This type of field is similar to that generated by Mercury. The field strength will range between 0.01 to 0.1 gauss. This type of field can be used for compass navigation but nothing else.

PMF3: Strong, global

This type of field is similar to that generated by Earth. Its strength ranges from 0.1 to 1 gauss (Earth's field is about 0.3 gauss). This strength of field will provide excellent protection from most radiation. The only exception would be a particularly powerful coronal mass ejection.

PMF4: Powerful, global

The strength of this field ranges from 1 to 10 gauss. It is very rare to see such a powerful field generated by terrestrial planets; however, it is common among the subjovian worlds. Furian terrestrial planets, and to a lesser extent, vesuvians, could generate a PMF this powerful.

PMF5: Jovian, global

Only Jovian or larger type planets could generate a PMF this powerful. The field strength ranges from 10 to 1000 gauss. This is the most powerful PMF found. At the higher strength range, even outside the radiation belts, PMFs of this strength are dangerous to living things, and lengthy exposure can be fatal.

PMF6: Lethal

Lethal PMFs are in the 1000+ gauss range. A magnetic field of this strength poses an immediate danger to any living thing, since the field is powerful enough to actually interfere with physical and chemical processes. This strength of field will never be found around planets, but near starspots on stellar primaries.

Magnetic fields beyond a million gauss cause atoms to be distorted into elliptical shapes, aligning along the magnetic field's lines of force. Even chemical bonds are overwhelmed and molecules will cease to exist. All matter loses its structure and becomes "magnetic soup." Fields of this strength only exist near the surface of special neutron stars called magnetars. The density of a magnetar is such that a thimbleful of its substance, sometimes referred to as neutronium, would have a mass of over 100 million tons (gasp!).

· Planets of mass 0.01 to 0.1 Me are restricted to PMF1.

  • Planets of mass 0.1 to 0.5 Me may be PMF1 or 2.

· Planets of mass 0.5 to 3 Me may be PMF2 or 3, depending on their rotation; less than 500 hours rotation will in almost all cases generate a PMF3 field, while slower rotation (> 500 hours) will generate a PMF2.

· Vesuvian and Furian planets may generate a PMF4 field if they rotate in less than 100 hours; otherwise they generate a PMF3.

  • Subjovian planets generate a PMF4 field.
  • Jovian+ planets generate a PMF5 field.
MagnetosphereDiagram.png
Diagram of a Magnetosphere

VanAllen.png
Diagram of Van Allen Radiation Belts

Geology

This is a very complex subject. I have a geology textbook that is over 1200 pages thick. And that is not including its TOC, appendices, glossary, and index. The complementary textbook on geography is over 700 pages thick. This subject is covered lightly below with a following section on the structure of an Earth-like planet (specifically Earth). For further information, do a Web search on geology, or start with this Wikipedia article. As aforementioned, be sure to visit the sites of scientific communities and universities.

All planets with solid surfaces have geology. Landform assemblages are shaped by sudden catastrophic events and slow, but inexorable, forces. There are four kinds of geology: passive, sporadic, cyclic, and active.

Passive geology is just that; passive. Planets with passive geology have either cooled enough to have lost internal heat capable of resurfacing the planet, or never had it in the first place. Landform assemblages are dominated by the remnants of past ages of activity, impact history, and weathering, if applicable. The terrain in passive geology is marked by impact craters and low, rolling mountains and hills, as well as fault cracks and cliff-like scarps. The terrain will generally be very ancient, measurable in billions of years. Mercury is a very good example of this type of geology.

Sporadic geology is very similar to passive, but in this case there is just a feeble ember still glowing at the planet's core, enough to power occasional tectonic shifts and highly sporadic volcanism. This will tend to add trace gases such as methane or sulfur dioxide to an otherwise inert atmosphere, but will have little effect on the overall terrain, which will tend to look like passive geology. Only a geologist, or an unfortunate explorer who could have sworn the volcano was extinct, would be able to tell the difference. Venus may be a good example of this form of geology.

Cyclic geology is generated by an active core that is blocked by an overly thick crust. This is often the case of low to middle-mass terrestrial planets. The geological cycle often undergoes quiescent periods for tens or even hundreds of millions of years until the trapped heat overwhelms fracture points in the crust. The situation then changes drastically, and global vulcanism takes place, sometimes capable of resurfacing huge areas of the planet within a few million years, if not the entire global surface. The atmosphere often thickens and becomes highly toxic, making life very difficult for complex forms. Eventually the pressure wanes, and the surface settles into quiescence.

Active geology take place constantly, with major earthquakes and eruptions every year or so. It comes in two distinct flavors: hotspot and plate-tectonic.

Hotspot geology occurs on terran planets, as well as occasional low-mass pelagic worlds. Mantle plumes of hotter material from deep in the mantle near to the core create zones of high pressure and excessive heating under the crust. Eventually this material breaks out in a region of high vulcanism. Because the crust is immobile, unlike plate-tectonic worlds, these hotspot regions give rise to massive shield volcanoes hundreds of kilometers across, sitting on extensive highland regions. On some worlds, they can grow over a thousand kilometers across, and rise high enough to poke out of the planet's stratosphere. Olympus Mons on Mars, and the Tharsis region, are very good examples of the results of hotspot geology. Also, the Hawai'i islands were formed due to both plate-tectonic and hotspot geology. Mars may now be of sporadic or passive geology. Since even sporadic geology may only be active every tens or hundreds of millions of years, we may never know.

Plate-tectonic geology is common on pelagic planets, where there is enough water to both fuel and lubricate the process. Unlike normal planetary crusts, plate-tectonic crusts are broken into a number of plates. Water from global oceans permeates the rock, lubricating it and allowing the plates to slide under each other in subduction zones. This causes tension stress on the far side of the plate, and new material is dragged/pushed up from below to fill in the gap. This often forms a jagged suture line, most commonly under the oceans themselves, and thus named mid-oceanic ridges. These ridges form a line of volcanic mountains often thousands of kilometers long. The subducted edges of the plates are easily melted since they carry water as an impurity, triggering volcanoes on the surface above and away from the subduction zone on the subducting plate. This complex and active process creates very young crust, often only a few tens to hundreds of millions of years old, and is dependent on large quantities of water. Continental crust lie on regions of lighter granites that are carried along like rafts, sometimes merging, sometimes being broken apart by the activity below them. Earth is a very good example of plate-tectonic geology.

Earth-like Planet Structure

Below text is borrowed from here: http://www.moorlandschool.co.uk/earth/earths_structure.htm (text has been corrected to American English).

Inner core: depth of 5,150 - 6,370 kilometers

The inner core is made of solid iron and nickel and is unattached to the mantle, suspended in the molten outer core. It is believed to have solidified as a result of pressure-freezing which occurs to most liquids under extreme pressure.

Outer core: depth of 2,890 - 5,150 kilometers

The outer core is a hot, electrically conducting liquid (mainly iron and nickel). This conductive layer combines with Earth's rotation to create a dynamo effect that maintains a system of electrical currents creating the Earth's magnetic field. It is also responsible for the subtle jerking of Earth's rotation. This layer is not as dense as pure molten iron, which indicates the presence of lighter elements. Scientists suspect that about 10% of the layer is composed of sulfur and oxygen because these elements are abundant in the cosmos and dissolve readily in molten iron.

D″ layer: depth of 2,700 - 2,890 kilometers

This layer is 200 to 300 kilometers thick. Although it is often identified as part of the lower mantle, seismic evidence suggests the D″ layer might differ chemically from the lower mantle lying above it. Scientists think that the material either dissolved in the core, or was able to sink through the mantle but not into the core because of its density.

Lower mantle: depth of 650 - 2,890 kilometers

The lower mantle is probably composed mainly of silicon, magnesium, and oxygen. It probably also contains some iron, calcium, and aluminum. Scientists make these deductions by assuming the Earth has a similar abundance and proportion of cosmic elements as found in the Sun and primitive meteorites.

Transition region: depth of 400 - 650 kilometers

The transition region or mesosphere (for middle mantle), sometimes called the fertile layer and is the source of basaltic magmas. It also contains calcium, aluminum, and garnet, which is a complex aluminum-bearing silicate mineral. This layer is dense when cold because of the garnet. It is buoyant when hot because these minerals melt easily to form basalt which can then rise through the upper layers as magma.

Upper mantle: depth of 10 - 400 kilometers

Solid fragments of the upper mantle have been found in eroded mountain belts and volcanic eruptions. Olivine (Mg, Fe)2SiO4 and pyroxene (Mg, Fe)SiO3 have been found. These and other minerals are crystalline at high temperatures. Part of the upper mantle called the asthenosphere might be partially molten.

Oceanic crust: depth of 0 - 10 kilometers

The majority of the Earth's crust was made through volcanic activity. The oceanic ridge system, a 40,000 kilometer network of volcanoes, generates new oceanic crust at the rate of 17 km3 per year, covering the ocean floor with an igneous rock called basalt. Hawai'i and Iceland are two examples of the accumulation of basalt islands.

Continental crust: depth of 0 - 75 kilometers

This is the outer part of the Earth composed essentially of crystalline rocks. These are low-density buoyant minerals dominated mostly by quartz (SiO 2) and feldspars (metal-poor silicates). The crust is the surface of the Earth. Because cold rocks deform slowly, we refer to this rigid outer shell as the lithosphere (the rocky or strong layer).

Growth of the inner core is thought to play an important role in the generation of Earth's magnetic field by dynamo action in the liquid outer core. This occurs mostly because it cannot dissolve the same amount of light elements as the outer core and therefore freezing at the inner core boundary produces a residual liquid that contains more light elements than the overlying liquid. This causes it to become buoyant and helps drive convection of the outer core. The existence of the inner core also changes the dynamic motions of liquid in the outer core as it grows and may help fix the magnetic field since it is expected to be a great deal more resistant to flow than the outer core liquid (which is expected to be turbulent).

Although the above is the structure for Earth, it can be used for other Earth-like planets.

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General Diagram of Earth's Structure

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Diagram of a Subduction Zone

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The Crystal Palace: Download Wallpaper

I included the above picture because it is an excellent example of some of the wondrous beauty geology can create. Read more about The Crystal Palace at National Geographic.

Oceanography

Some planets have a layer of liquid, either just below a solid, icy crust or sitting above a rocky one. These layers may range from isolated little seas to vast global oceans up to thousands of kilometers deep. Most planets have little or no surface liquid, but even they may play host to subterranean aquifers or permafrost on colder planets. Sometimes an entire ocean may be concealed below a shell of ice many kilometers thick.

Planets with seas or oceans are often the most sought after by space-faring civilizations, since it is these that have the greatest chance of supporting and harboring complex life of their own.

Composition

Most oceans in the universe are composed of water. Water is one of the most common substances in existence, and it has a broad range of temperatures and pressures at which it is liquid. Water may be quite pure, but most often carries a number of impurities. Depending on the planetary conditions, oceans may be saline, or even somewhat acidic or alkaline. Extreme concentrations of impurities are more common in smaller bodies of water. Second to water, liquid hydrocarbons like methane and ethane can sometimes form seas and oceans under conditions of sufficient atmospheric pressure and low temperatures, but such planets are rarer than aqueous ones, and confined to the outermost half of the system.

Hydrography

Many planets have no surface water at all, but larger ones are generally wetter. Some larger planets only bear small numbers of contained seas dotted about the surface. Others can be partially or totally covered by oceans. Oceanic planets host global oceans a minimum of a hundred kilometers deep. As well as liquid oceans, planets may also develop mantles of ice near their poles, called polar caps. If you have something specific in mind, choose from the options in the below table. Otherwise, for randomness, you may consult the tables below.

Terran Pelagic Oceanic Vesuvian Furian
01-90 01-10 01-90 Only Exsiccated planet. There is no surface water. Permafrost or subsurface aquifers are possible on some planets.
91-00 11-30 91-00 Arid planet. Global hydrography is <= 20% (d20). Seas are few and shallow. Most surface water is ephemeral in nature. Any permanently standing water will be exceptionally saline.
31-60 Semi-aqueous planet. Global hydrography ranges between 21-50% (d30 + 20). There can be large bodies of water, but the planet is still dominated by deserts overall. There is usually enough water to generate some plate tectonic geology.
61-80 Aqueous planet. Global hydrography ranges between 51-80% (d30 + 50). This type of planet is very Earth-like, dominated by oceans with isolated land masses. Plate-tectonic geology is inevitable.
81-00 Only Oceanic planet. Global hydrography is >= 90% (d10 + 89). Only scattered atolls and chains of small volcanic islands exist.

-20 modifier for planets in systems dominated by Jovians in eccentric orbits.

Subsurface Hydrography for Glacial Planets
01-20 Frozen planet. All water is completely frozen. Only helium can exist in liquid form.
21-60 Semi-liquid subsurface. The overlying mantle of ice contains some regions of slushy ice that is capable of flowing. The slushy ice is not truly liquid water.
61-80 Discontinuous subsurface ocean. A subsurface ocean exists in tidal stress zones (see Chapter 5: Moons) or volcanic hotspots warmed from the interior. Overall hydrography is 40-60% (d20 + 40).
81-00 Global subsurface ocean. The subsurface ocean is contiguous with little or no interruption. Overall hydrography is 70-90% (d20 + 70).

Shared Orbits

Before one can understand Shared Orbits, one must first grasp the five Lagrange Points and the Hill Sphere, or Hill Radius.

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Diagram Showing Contour Plots of the Effective Potential of a Two-Body System
Due to Gravity and Inertia at One Point in Time and Showing the Five Lagrange Points and Hill Radii

In any orbital system involving a primary and secondary (planet and star, planet and moon, moon and planetoid, etc.), there are regions where the gravitational attractions between the two bodies cancel out and nullify each other. These points are called Lagrange points, after the mathematician who discovered them (Joseph Louis Lagrange). Of particular interest are points L4 and L5, since these are the strongest and most stable. These are located 60 degrees to either side of the planet at the same distance from the sun. Bear in mind that unless the orbit is near-circular, this does not mean quite the same thing as being ahead of and behind the planet in its orbit. Matter that falls into these areas remains stable there, and can form asteroid fields or perhaps even planets. Jupiter plays host to the Trojan asteroids, two rich clusters of asteroids that occupy its L4 and L5 points. The mysterious object that is supposed to have hit the Earth and formed the Moon is supposed to have formed in Earth's L4 point and been driven out by perturbations from other young planets, eventually to collide with Earth. These shared orbit relationships are more stable if the central planet is at least three times heavier than any secondary planets.

Shared orbits can be used to save a planet that would otherwise be forced out by another planet's highly-elliptical orbit. GM's discretion applies here of course, but be sure not to overdo it. Remember that even Jupiter only has asteroid clusters at its L4 and L5 points, and Earth's hypothetical L4 companion, Theia, became unstable and was destroyed. In nature, such shared orbits are very rare; the only known stable examples occur in two pairs of miniscule moons orbiting Saturn. Perhaps a good proportion of shared orbits are one such event per 1000 or 10,000 systems, perhaps even more rare.

It must also be remembered that the greater the mass difference between the two main bodies, the more unstable the L4 and L5 Lagrange points are as in between Sol and Earth. Also, near equal mass bodies in the next inner orbit will also tend to destabilize these points. This explains how the Trojan Asteroids can exist since there is no planet between the orbits of Mars and Jupiter to disrupt them as Venus would do to any that may have shared Earth's orbit. And it can explain why Saturn only has miniscule planetoids at its L4 and L5 points. Uranus and Neptune have no Trojans at their L4 and L5 points.

The Hill Sphere, also called the Hill Radius, basically, is a toroidal region around a planet where a satellite is safe from either falling into the planet becoming rings or being torn away by the primary into its own stable orbit. Use the below equation to calculate the Hill Radius.

\[R = a(1 - e)\sqrt[3]{\frac{m}{3M}} \]

Where \(R\) = Hill Radius; \(a\) = mean orbital radius; \(e\) = orbital eccentricity; \(m\) = mass of the smaller object; \(M\) = mass of the heavier object.

Notes: The unit for Hill Radius will be dependent on the unit used for the mean orbital radius (MOR). If you use kilometers for the MOR, then the Hill Radius will be in kilometers. The units for both masses MUST be the same.

Since their first discovery, the L1 and L2 points have since been found to be unstable. An object at the L1 point would need to orbit the primary at a slower than needed rate to stay in that orbital point, and thus it would actually end up falling towards the star, further speeding it up and causing the object to leave the L1 point. An object in the L2 point would have to orbit faster than needed for that orbital point, forcing the planet into a higher orbit and causing the object to leave the L2 point. However, for a short time, a few tens to a few hundreds of millions of years, an object may orbit in the L1 and/or L2 points.

Binary Planets

For a very good example of a binary planet, read the Rocheworld series (especially the first two books: Flight of the Dragonfly (republished as Rocheworld) and Return to Rocheworld) written by Dr. Robert L. Forward. Although written as science fiction, it is largely based on hard science fact. In my opinion, Dr. Robert L. Forward was the best hard science fiction author ever. But that is just my opinion.

Binary planets are a very rare expression of an extreme shared orbit. The two planets actually form in a binary partnership. Capture events are not possible, since any wandering planet will be moving too fast. Binary planets form within the same mass class of each other (within 10% of each other). They are also of the same density (within 5% of each other) since they are made from the same material.

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A Sample Binary Planet

Because the two planets formed out of the same material in the same place, they will be very similar. Thus, rolling for one will also determine the type for the other. The only exception is that one may be completely covered by ocean while the other is a dry, arid dust-ball as in Forward's Rocheworld in which one was named Eau Lobe and the other named Roche Lobe.

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Robert L. Forward's Rocheworld

Important Note: Only terrestrial planets can become binary planets. Also, the maximum size for each body of a binary planet is Oceanic. Any binary planet larger than two Oceanics will simply pull together to form a Vesuvian or Furian.

Binary planets have what may be called a double rotation. However, it is more accurate to say that the binary planet spins and rotates. Both bodies in a binary planet will spin in the same direction, NO exceptions. Both bodies will also rotate about each other around a common center point, NO exceptions. Due to the gravitational attraction to each other, both bodies will be somewhat egg-shaped with the more pointed end towards each other. Determine spin and rotation as you would for any other planet. Spin and rotation need not be the same length of time, although they could.

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Diagram Showing Spin

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Diagram Showing Rotation

Needless to say, the combined spin and rotation will lead to some wildly varying daylight/nighttime periods. Although they will form a predictable cycle, the cycle could be as short as a few local days, or spread out over a few local years. I am afraid that you are on your own figuring this out since discussing how to determine it could involve writing a textbook.

Double Planets

The major difference between Binary Planets, Double Planets, and Planet-Moon systems is size and orbiting distance. Where a Binary Planet system has two objects literally equal to each other, a double planet can have two objects of near equal mass to two classes different. Generally, the less massive object will be within ×0.5 of the mass of the more massive object. Where a Binary Planet system has two equal objects in very close proximity of each other, a Double Planet system has a greater distance apart from each other. For this SSG, a double planet is based upon the location of the barycenter of the two celestial objects. If the barycenter is located outside of both objects, then it is a double planet system (like Pluto-Charon). If the barycenter is located inside the more massive object, then it is a planet-moon system (like Earth-Moon). Also, in a Double Planet, both objects need not be of the same type. For example, you could have an Oceanic-Terran double planet. Furthermore, both objects in a double planet may or may not have tidally locked to each other, meaning they keep the same face towards each other. Usually, if the system is 6+ billion years old, the double planet will have tidally locked to each other. However, if the mass difference between the two bodies is great enough, the more massive object may not be tidally locked, but the lesser massive object will usually be tidally locked like the Earth's moon, unless the double planet system is fairly young (< 2 billion years).

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Diagram of Planet-Moon Barycenter

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Diagram of Double Planet Barycenter

Nemesis Events

This is named after the ancient hypothesis "Nemesis". These are events that may be caused by one of the following objects: brown dwarf, white dwarf, or neutron star. For the purposes of this discussion, "Nemesis" refers to any massive object that can perturb the entire stellar system. If you are into pseudo-science, Nemesis could even be a gravimetric expulsor, quantum filament, etc. The premise of this hypothesis was that there was an exceptionally difficult to detect brown dwarf, white dwarf, or neutron star that orbited the sun in a highly elliptical orbit of about 50,000 to 100,000 AUs, completing one orbit every 26 to 50 million years. The hypothesis was originally proposed as a possible explanation of the mass-extinction events on Earth every 26 to 50 million years. However, in the almost 30 years since the proposal of this hypothesis, there has been no proof discovered. Since the last mass-extinction was approximately 5 million years ago, that means if there is a Nemesis, then it should be close enough to detect (within 1 to 1.5 ly). And unbelievably as it may sound, some of our tax dollars are being used towards the attempt of detecting Nemesis. If Nemesis is a black dwarf (not possible) or a brown dwarf, it would be nearly impossible to detect it. Personally, I think the Nemesis hypothesis is just that; a hypothesis. However, if you wish to have something like a brown dwarf, white dwarf, or neutron star that is a Nemesis for your system, then put it there. You will just have to calculate its orbital period. Just remember, even if the Nemesis has passed through the transplanetary region, it could get halfway back from its periapsis to its apoapsis before any objects from this region actually threaten the inner planets of the system. Also, unless there is an exceptionally sophisticated detection system, such threats may not be detected until it is too late to do anything about it.

Nemesis events can literally be anything that can cause a cataclysmic event. It could be something as simple as perturbing comets from the Oort Cloud and/or Kuiper Belt into the inner system. It could be something as cataclysmic as perturbing the focus planet out of its orbit caused by the Nemesis falling through the system from a highly elliptical orbit, such as passing through from above or below the ecliptic. Or, even the worst case; the Nemesis could collide with the focus planet, or pass close enough that the focus planet is completely disrupted due to the Nemesis passing within its Roche Limit of the planet. Nemesis could pass close enough to perturb the focus planet's moon into the planet. How about the even longer term effect of perturbing the system's Prime Jovian into the inner system?

I could continue, but I think your imagination is good enough. Just think about it.

Prime Jovians

Since we have been discovering systems with Prime Jovians are rarer than first thought, I felt this subject needed some further discussion. Just for a real world example, the table below shows the effect of a Prime Jovian (Jupiter) on our system. This table only focuses on the main eight planets of our system, basically comparing Jupiter to the other seven.

Planet Mass Volume
Mercury 3.302e23 6.083e10
Venus 4.8685e24 9.2843e11
Earth 5.9736e24 1.08321e12
Mars 6.4185e23 1.6318e11
Saturn 5.6846e26 8.2713e14
Uranus 8.6832e25 6.833e13
Neptune 1.0243e26 6.254e13
Total 7.6953615e26 9.6023565e14
Jupiter 1.8986e27 1.43128e15

Note: The above data was retrieved from JPL's Planetary Data Sheets site.

As can be seen, Jupiter out-masses (×2.4672) and out-sizes (×1.49055) all other planets combined. Including the planets from an old campaign (Udava) ran by my wife and me, below is an image showing the size comparisons of all these planets. As unbelievable as it may seem, the planet Bangera actually out-masses and out-sizes all other 18 planets in the image. In fact, Bangera was a borderline Brown Dwarf-Hyperjovian planet. And this system was generated from the second revision of the first SSG I wrote way back in 1983.

I even used this image as an example of how actual 3-D objects would make poor symbols in a cartography class. In fact, 1‑D objects are the most perceptible when seeing size change. 2-D objects are little harder to visually see a size change. However, 3-D objects are the most difficult in perceptualizing a size change. As said, although it may not seem so, Bangera actually has a volume almost 2.1 times the volume (almost 2.4 times the mass) of all other 18 objects combined. Because of our perception, we tend to see the 2-D part of the objects (the diameter) and add that together. Our eyes do not truly perceive a three dimensional size increase. Our eyes more readily see a 2-D size increase instead. Furthermore, our eyes will more readily see a 1-D size increase than seeing a 2-D size increase. Something to remember when symbolizing your maps.

In case you are wondering, yes, all objects in the below image are true to scale in the 3-D. Even if you were to only look at the objects in our stellar system, Jupiter, Saturn, Uranus, Neptune, Mercury, Venus, Earth, and Mars, would you believe that Jupiter has almost 1.5 times the volume of all other seven planets in our stellar system combined?

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This leads me to think that if we never had a Jupiter, how many other planets our system might have contained. Makes one wonder… If Saturn had been the Prime Jovian, we might have had a planet where the asteroids are now and perhaps another terrestrial type planet between it and Saturn. We shall never know…

Now that I think about it, I ought to go back and see if Bangera was actually fusing deuterium and may have been a Brown Dwarf. I think it would be neat to have Udava orbit Bangera as a moon. With Bangera actually fusing deuterium, it would add some warmth to Udava, making it a more viable planet for life further from the stellar primary. Hmm…

Although I could run wild with my fignations of imagiments, I still tend to stick to feasibly possible instead of making off the wall pseudo-science within my stellar systems. However, I may still add some pseudo-science elements such as my ManaStorms, ManaConvulsions, ManaSurges, and ManaEruptions, but I still tried me damned best to describe them within our current understanding of physics.

Editor's note: The entire Stellar System Generator article is available as a pdf. In addition, the datasheets used to record data for stars and planets using the system developed in the articles is also available as a pdf.