The Bones of Earth 3: Worlds In Space

The Bones of Earth 3: Worlds In Space
By Jubal

So, having done The Bones of Earth 2 on more unusual fantasy world ideas, here are some thoughts on some sci-fi world building – how we can take into account the conditions in which planets form and their physical characteristics emerge, and some hints on how that might translate into world-building and the basis of different settings. One of the major issues with sci-fi is that we frequently have to work on an inter planetary scale, such that it's often hard to do more for planets than "this one's an ice planet" or "this one has trees", whereas of course planets should have a wide variety of different biomes. Whilst the sheer scale makes it hard to envision entire planets, thinking about how they work physically may be a helpful place to start. So without further ado...

Diameter and density

There are two things these affect; firstly, the planet's size, and secondly its surface pressure. Size is fairly self-explanatory – a planet with a larger area has more surface on which to fit continents, etc. Pressure is more complex but worth considering for sci-fi settings in particular: it relates quite heavily to density. If you, for example, had a planet which was the same diameter as earth but more dense, then the surface gravity would be higher. There's also the question of atmospheric density as well; a dense atmosphere will mean more pressure at surface level. This, in turn, affects how evolution might take its course at the planet's surface. A high pressure world will make it harder for plants to grow tall and animals to move, likely leading to stockier and more muscular forms of life, and vice versa. It also affects what sort of structures can be supported – exoskeletons, for example, have something of a size limit on earth, because the weight of the external plates becomes too great above a certain point. In a world with lower gravity, insectoid creatures could be much larger as a result of the lower pressure & gravity.

Volcanicity

Venus is an incredibly volcanic planet; having suffered from a form of runaway global warming as a result aeons ago, it's pretty much a sulphurous, burningly hot hell-hole. Earth, with moderate volcanicity, is considerably more pleasant. Other planets that have no volcanicity at all will often correspondingly have no atmosphere at all, which doesn't tend to bode well for the future of life thereon. In other words, volcanoes and having a hot core to a planet are vitally important to life, but within certain levels. Life evolving on a high-volcanicity planet, or whose planet somehow became more volcanic, might have need to adapt to higher levels of toxic gases and extreme heat. The reverse situation, perhaps more likely, might be if a planet with little life was "dying" as a result of its volcanoes steadily going dormant and insufficient carbon dioxide being pumped out to replace losses. Volcanoes of course also shape the landscape – be that shield volcano mountains, volcanic plains, or simply the fact that volcanic ash is rich in nutrients and tends to lead to areas of very fertile soil in the locality.

Orbit

Orbit affects solar radiation levels; too close to a sun and the planet is burnt to a crisp, too far out and it is frozen solid. However, how far out that is depends on the size and heat of the star; it's also not always the case that an inhabited body will primarily orbit a star. Gas giant planets have large moons which could equally be the basis for space colonies if not life itself. Stars need not necessarily be sun-like, either, and systems with two suns certainly exist – though in a system with a much larger or much smaller star, or a binary star system, the whole planetary system could end up rather more volatile; only a third of binary star systems have planets, whereas the majority of sun-like stars have some.

Spin

Warmth and radiation levels are also affected in terms of how different parts of a planet experience them by spin. Spin is integral to planets forming – the disk of particles from which planets form is only thrown out by their star spinning in the first place, and that spin then leads to any eventual planets still having their own spin as well. A planet that spins fast will have shorter days, a planet that spins slower will have longer ones. But that's not all: a planet doesn't actually necessarily spin on exactly the same plane as the one in which it orbits its sun, and the tilt is what causes seasons – the bigger the tilt, the sharper the seasonal effects. One final thing to think about is planets that don't spin, or rather don't appear to – these "tidally locked" bodies often end up with one side constantly facing their star (an effect we can see in our own moon, one side of which is never visible from earth). This could easily lead to extreme differences of climate on a planet, with a thin "habitable" zone at the edges, and an inhospitable a hot face and cold face. Any inhabitants might either need to stay in the habitable zone, or have some pretty serious adaptations to allow them to venture into the extreme regions of their world.

And there you have it! I hope this was useful, and helps you build some worlds where your characters, players, or whoever can develop in a more natural-feeling way based on the properties of the little ball of rock they're clinging to as it passes through space. Sometime in the next few weeks I'll hopefully get to finishing The Bones of Earth IV, so stay tuned for that - in the next article in this series, I'll look at different varieties and styles of maps commonly used in SFF fiction and hopefully help you get closer to drawing your own.

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