Alien Biospheres: Part 1 – The Planet (ft. Artifexian)


When building a fictional world, one of the
very first things to consider is what kind of animals, plants, and people are going to
inhabit it. Are the lifeforms the same as or similar to those on found earth, or are they entirely different? What’s the climate like? What kinds of biomes and ecosystems are present?
Depending on the type and style of world you’re building, the answers to these questions can
vary dramatically, but for this series, we’re starting totally from scratch. We’re going
to evolve a scientifically feasible alien biosphere using the principles of evolution. Of course, this will all be entirely speculative,
since so far, we only know of one instance of life occurring in the universe, but any
alien life would be subjected to the same laws of nature as life on earth, so by studying
our own biosphere, we can make some predictions of what aliens might be like. But before we can make an alien planet, we
have to make, well… the alien planet… as in all the non-living stuff. We’ve got
to lay out some groundwork about what this planet is like, since this will have a heavy
impact on how its resident lifeforms will evolve. Now, planet-building can be a huge rabbit-hole
in and of itself, and it’s kind of out of my wheelhouse, which is why I’ve brought
Artifexian along to help. Hello! So, where do we begin? Best place to start is with a rough brief.
What are you looking for? Well, since I’m going to be evolving the
biosphere from the very beginning of this planet’s natural history, we might want
to start out with something similar to the conditions of ancient earth, but maybe tweak
a few things to subtly influence the way life develops; keeping in mind of course, that
the further we stray from earth-like conditions, the more complications are introduced, and
the more speculative things will get when designing the biosphere, so we should probably
err on the side of too earth-like. Sound good? Perfect! That’s very doable. I already have
a bunch of neat ideas. But first, let’s start with your star. Or stars …? I think just one will suit our purposes just
fine. Let’s not get crazy…at least not yet. Alright, one star it is. Let’s set the star’s
luminosity to 75% that of Sun. Doing so mimics the output of our Sun during the Archean Eon—2.5
– 4 billion years ago. With the luminosity set, we can derive a number of stellar features,
most notably your stars habitable zone—the region around your star where liquid water
can exist on the surface of a planet. No water, no life so knowing this zone is important.
If we have your planet orbit a distance of 0.85 AU, its average temperature will be about
20ºC which is hotter than Earth but nothing crazy. This will also mean that its year will
be roughly 298 Earth days long. Happy so far? Yep, works for me. With all that in the bag we can move onto
the planet itself. To construct your planet we need to figure out its mass, radius, surface
gravity and density. All of which are related like so. Ooh!? Can we make it a low gravity planet?
I quite like the idea of working with megaflora and megafauna. Definitely. We could keep your planet the
same size as earth, again nice and familiar but drop the gravity to 80% Earth gravity. Hmmm, could we go lower? Not really. Any lower and the density will
be such that your planet won’t have an iron core. No iron core, no magnetic field, no
life. Alright then, 80% gravity it is. In terms of day length and axial tilt, we
know that an Earth day was much shorter in the past and that the earth’s axial tilt
varies over time. So, let’s make your day about 20 hours long and give your planet 22º
of axial tilt. This lower axial tilt means that overall your planet will be subject to
slightly reduced seasonal variation. You ok with that? Yep, as long as there’s at least some seasonal
variation, I’m happy. Now, what about my atmosphere. I suggest emulating Earth’s atmosphere as
closely as possible. Messing with the atmosphere can be … well … messy. Some might say interesting … Oh, boy, I don’t like where this is going.
I mean, 1.5 billion years ago, oxygen was super low and CO2 super high. So, riffing
off that I can do something like this. But that’s really not very … Ah c’mon, surely we can do something more
interesting than that! How about we say 1% of the atmospheric composition is taken up
by hydrogen sulphide? You … you want to add hydrogen sulphide?! Sure, I mean it exists in small quantities
on earth, including as a metabolic byproduct, and some organisms live off the stuff, so
how about we throw in a tiny bit extra, just to mix things up a little. Ok, if you insist but just be aware that the
oxygen is below what is recommended for carbon based, humanoid lifeforms. The CO2 is far,
far, far above what is recommended or safe. And the hydrogen sulfide … well … it’s
not recommended at all. Don’t worry. I’ve totally got this…
I think. I hope so. Anyways, what’s left? A moon. Yes, let’s just stick with one moon for
simplicity, and can we make it so that it creates fairly large tides? Sure, one way of doing this is to place your
moon close to your planet. Let’s say it orbits about 50 earth radii out which will
give it an orbital period of 22.97 earth days. Also, let’s make your moon 50% more massive
than our Moon. The increased mass and closeness will give you tides about 2.7 times greater
than those we experience on Earth. Now, obviously this will vary wildly depending on local geography,
nevertheless it’s a good ballpark. Looks great! Speaking of local geography,
I think the last thing I’ll need is some landmasses. Since I’m going to explore a
big chunk of the planet’s natural history, I’ll need to know how the continents are
going to drift over a period of a couple hundred million years or so. As we’ll see, the shape
of the land has a pretty huge effect on how life develops. Sure, what are you thinking? Well, I thought it would be cool to start
off with a pangea-like supercontinent. Aha. And then have it break apart into two continents Yup. Only for them to rejoin later. Sure. And maybe an island continent could also break
off at some point too. Done! You happy with this timescale? Yes. That looks perfect! Cool, so there you go: a star, a planet, a
moon, a totally non-controversial atmosphere, and some landmasses. Excellent! Thanks very much for all your help,
Artifexian, it’s been a pleasure having you. Not a problem, the pleasure was all mine. And if anyone is looking for more on how to
construct their own alien planet, and if you’ve somehow never heard of artifexian before,
go and check out his channel for all the info you could ever need.
As for my planet, I think we’ve got just about all the bases covered, so next up…
let there be life!

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