#space building

[dziubomir]

[theticklishpear]

(A table of contents is available. This series will remain open for additional posts and the table of contents up-to-date as new posts are added.)

Part of Fifteen: Further Research and Resources

AKA What Pear Read To Write This Series

I read a lot of stuff in preparation for writing this series of posts. Researching and writing each post usually took about 3-5 hours. Here's most of what I read and watched, though admittedly not all of it, and yes, I did go out and read some very basic, elementary-school-level things sometimes to make sure I wasn’t misremembering things or misrepresenting them.

My biggest suggestion is: When in doubt, go to Youtuber Artifexian. He goes through all the math and how it’s related to what, and even has conlang and calendar creation videos. You’ll see him pop up a lot on these lists.

For hard sci-fi writers looking for all the math equations, go through the video descriptions for the Artifexian videos linked below. He explains what each equation means and why you should bother with it.

Solar Systems:

Formation of the Solar System from Artifexian

Solar System Tutorial

Creating a realistic world(s) map - planetary systems

Other Planetary Systems from Artifexian

How to Create a Classical Planetary System from Artifexian

Stars:

Stars from Nasa’s StarChild

The Sun and Other Stars from BBC

Star Types from Enchanted Learning

How to Build a Star from Artifexian

Multi-Star Systems:

Can there be more than one star in a solar system, and if so how would it work?

Modelling a multi-star system with numerous planets and moons

Introduction to Multiple-Star Systems from Artifexian

What Are Multiple Star Systems from Universe Today

How Do Multiple-Star Systems Form? from Phys.org

Alien Planets With Extra Suns Can Have Strange Orbits from Space.com

Planet ‘Reared’ by Four Parent Stars from Nasa

Planets:

Discovering Planets Beyond: How Do Planets Form? from Hubblesite

What Kinds of Planets Are Out There? from Nasa

List of Planet Types

Dwarf Planets: Science Targets from Nasa

Building Dwarf Planets from Artifexian

Building Gas Giants from Artifexian

Gas Giant Myths from Artifexian

Extrasolar Gas Giants from Artifexian

Building Terrestrial Planets from Artifexian

The Trouble with Terrestrials from Artifexian

The Habitable Zone:

The Habitable Zone from PennState’s ASTRO 801 course

Planetary Habitability

Orbits:

What is an Orbit? from Artifexian

Building Gas Giant Orbits from Artifexian

Building Hot Jupiter Orbits from Artifexian

Building Terrestrial Planet Orbits from Artifexian

Building Gas Giant Moons from Artifexian

Building Terrestrial Planet Moons from Artifexian

Asteroids:

What is the difference between a meteor, a meteoroid, a meteorite, an asteroid, and a comet? from Hubblesite

Asteroids: Fun Facts and Information About Asteroids from Space.com

The Kuiper Belt from Nasa’s New Horizons

Planetary Considerations:

Seasons:

Interplanetary Seasons from Nasa

Weather, Weather, Everywhere? from Nasa (yes, the images are broken, but the information is still there)

Tidal Locking

Axial Tilt from Artifexian

Day/Night Cycles:

What Causes Day and Night? from Universe Today

How the Earth Works: Night and Day from howstuffworks

Rotation of Planets Influences Habitability from Astrobiology Magazine

Solar/Sidereal Days from Celestial North

Surface Features:

Terrestrial Planet Geology from the University of Colorado Boulder’s Labratory for Atmospheric and Space Physics

How Do Planets Evolve? from Earthbound

Skies:

Why is the sky blue? from Nasa’s Space Place

Why do the planets have different colors? from Cool Cosmos

Could the sky on a planet theoretically be any color?

Why does the sky change color?

Why is the sky never green?

Life in Space:

Living in Space from NASA

Life in Space from Space Station Kids

What’s It Like to Live in Space? from LiveScience

What it’s REALLY like to be a NASA astronaut living in space for a year from BusinessInsider

Astronauts Answer Student Questions from NASA’s FAQ series

How Do Astronauts Go To the Bathroom in Space? from LiveScience

Astronaut Tips: How to Wash Your Hair in Space from the VideoFromSpace Youtube channel

Health in Space:

The Human Body in Space from NASA

What Happens to the Human Body in Space? from Smithsonian Magazine

The Health Risks of Space Travel from Healthline

Working in Space:

Repair in Space from iFixit.org

7 Things You Always Wanted to Know About Spacewalks from National Geographic

Progressing Toward Interstellar Travel:

The 12 Greatest Challenges For Space Exploration from Wired

10 Technology Innovations Needed For Deep Space Exploration from Science Channel

How Humans Could Go Interstellar, Without Warp Drive from Discover

Artificial Gravity’s Attraction from Aerospace America

Generators:

Planet Generator

Donjon Fractal World Generator

Space Engine Universe Simulator software

Additional Resources:

Fantasy World Building: Star Systems and Other External Influences

Worldbuilding Links and Software (an extensive list of calculators and generators and extra reading for hard sci-fi)

Worldbuilding (more links to various research including physics, cosmology, geography, natives, flora, fauna, and culture)

World Generation: Generic System & Planet Building Resources (a literal book)

Further discussions on planet-building

Literal Books From My Childhood: (Yes, I understood they were outdated in some areas.)

National Audubon Society First Field Guide: Night Sky

The Universe from Life Nature Library

Planets from Life Science Library

If there’s a topic I didn’t cover or that you’d like to see more on, feel free to drop in a request for it and I’ll work on adding it. These series are always open to additions, and those topics can come from you!

[theticklishpear]

Table of Contents:

Part One: What’s on the Horizon (a disclaimer) Part Two: Genre Goals and the Science of It All Part Three: The Birth of Stars Part Four: The Birth of Planets Part Five: Multiple-Star Systems Part Six: Types of Planets Part Seven: Determining Orbits Part Eight: Asteroids and Other Debris Part Nine: Moons, Moons, and More Moons Part Ten: How a Planet Gains Seasons & Plotting Environmental Zones Part Eleven: Day/Night Cycles Part Twelve: Surface Features Part Thirteen: Look to the Skies! Part Fourteen: Putting It All Together A Diversion: Contemporary Life in Space Part Fifteen: Further Research and Resources

(Note from Pear: This series is indefinitely open to new posts. As they are added, this post will be updated. Like always, you can find original content in the posts by pear tag and the table of contents tag for series.)

[theticklishpear]

(A table of contents is available. This series will remain open for additional posts and the table of contents up-to-date as new posts are added.)

Part Nine: Moons, Moons, and More Moons

Just like how planets orbit a star and the stars orbit the center of a galaxy, and two stars might orbit each other, and two pairs of stars might orbit each other, and asteroids sometimes orbit each other, so too do planets get their own tag-alongs orbiting them. These celestial bodies--natural ones, mind, not constructed ones--are called moons or satellites.

Moons are defined by both size and composition. Major moons have enough mass that they retain a mostly spherical shape while minor moons are smaller, with less mass, and therefore are frequently oddly shaped. The key to size and shape is 200-300km in size, with minor moons being less than that size and major moons being larger. Moons tend to be comprised of either rock or ice, depending on where in the system it’s located. Obviously, like the formation of icy planets, icy moons must form outside the frost line.

Gas Giants:

Moons collect around gas giants in kind of three groups:

Small, irregular rocky minor moons gathered in an orbit on the outer edge of where the planet could potentially have rings. They are generally only 10-100km in size and make sure to leave 0.25-1.5 Earth-radii of space between each other.

A handful of large major moons gathered in orbit outside where the planet’s rings are. They leave more than half the planet’s size between each other. They may even have minor moons of their own.

Tiny, irregular minor moons--often captured asteroids--orbiting distantly, at the very edge of where they’re able to orbit. Generally in the 10s of kilometers in size, these minor moons orbit on very eccentric and inclined paths, and sometimes even backwards (retrograde).

Don’t forget! Moons clear out the debris from their orbits paths! So if you position a moon in the midst of a gas giant’s rings, they’ll create a gap in the rings where they orbit. Some major moons of gas giants cause major gaps in the rings, even though they’re not actively orbiting in the rings to clear it out. The reasons for this are a bit complex, but if you wanted to build a ringed gas giant with a major moon close-ish to the planet and a major gap in its rings, you totally could!

Terrestrial Planets:

Terrestrial planets don’t tend to accumulate many moons. They may have enough gravity to pull in some asteroids to become moons, like Mars’ two moons. (Remember that asteroids are mostly chunks of rock that are small enough that they would be considered minor moons.) To go along with this, distant planets are likely to have more moons, and close-in planets will have less.

It’s pretty rare for terrestrial planets to have a major moon, however if you’re looking for your terrestrial planet to become habitable, your planet must have at least one major moon. The gravity of the major moon helps to stabilize the planet’s axial tilt, therefore helping to stabilize and regulate seasons. Terrestrial major moons tend to orbit close to their planets in the same direction as their planet (prograde), with nearly circular orbits (low eccentricity), and with a low level of inclination, that is, generally pretty close to around the central plane of your planet.

Knowing that you definitely want a major moon for your habitable terrestrial planet, and knowing that it needs to be larger than 200-300km in size, it’s an interesting note that your moon ought to be smaller than your habitable planet.

Remember: Your terrestrial planets really shouldn’t have major moons. It’s rare, and only your habitable planet should have them. All other terrestrial planets should have minor moons.

Minor moons have significantly less gravitational impact on their planet, since they’re pretty small. This means their orbit doesn’t have to be “close” like with major moons. They can orbit pretty much as near or far as you’d like them to. Remember that the closer to the planet they orbit, the shorter their orbital period will be, which impacts your planet’s moon phases.

If your planet has more than one moon, make sure they’re not within the distance of 5 of the planet they orbit from each other. That goes for any type of moon!

Habitable Moons:

The closer a terrestrial habitable planet’s moon is to its size, the more likely it becomes that the moon may also become habitable.

Gas giants can also have habitable moons, but only if the gas giant moves into the habitable zone. Maybe it moves into the habitable zone and captures an already habitable planet as its moon, or the gas giant already has a rocky moon that’s built like a terrestrial planet that it brings with it as it migrates into the habitable zone.

Now, it’s important to understand that these kinds of scenarios are really, really rare. A habitable planet is estimates as needing to be at least a quarter to 2 times the mass of Earth, and for now, that’s way more massive than most moons, and in order to follow the ratio size guideline for major moons around a gas giant (outlined in the resources to come), its gas giant would have to be enormous (we’re talking, like, 7-8 times the size of Jupiter, approximately). Not only that, but any moon formed outside the frost line and migrated inward would likely be an icy moon, and once that melts, you’re not dealing with a terrestrial planet, but a water world.

If you’re going to try to build a habitable moon, your best bet is likely the captured already-established habitable planet theory, orbiting on a non-eccentric path (less than 0.01).

Next up: Seasons!

[theticklishpear]

(A table of contents is available. This series will remain open for additional posts and the table of contents up-to-date as new posts are added.)

Part Six: Types of Planets

I wish I could say what we’re going to talk about next is a complete and perfect list of the types of planets that could form in your created systems. Unfortunately, we just don’t know enough about our galaxy and universe to be able to say that for certain. What I can say is that this is our current best guess.

As I said in Part Four, planets form out of the spinning cloud of debris around the star. As they pick up whatever happens to be in their path, they gain mass, and spin together into planets with specific elements creating their cores. From what we’ve observed so far, every planet has some kind of highly dense core, even the gas giants who boast thick gaseous envelopes around their cores. There’s a correlation between a planet’s mass and radius that helps us determine what a planet is most likely to be composed of. Check it out:

R in the above graph means radius, as measured in Earth’s radius, and M is a planet’s mass, as measured by Earth’s mass. The solid lines note homogeneous planets, that is, those that are comprised of a single material: Hydrogen, water, silicates, and iron. The dotted lines denote planets formed from mixes of materials, like Jupiter and Saturn as mixed hydrogen and helium planets, and water worlds composed mostly of water with silicates and iron in various percentages. These types of planets are not considered capable of sustaining life.

One chief characteristic of a habitable planet is that they’re thought to be considered “terrestrial,” and in order to be terrestrial, a planet has to be considered rocky and composed mostly of carbon, silicate, and/or metals. Those planets are marked on the above graph using the red-orange and green colored lines, varying from pure silicate worlds, Earth-like silicate-dominant worlds with iron cores, planets with silicate mantles and more massive iron cores, and those comprised of a pure iron core.

Take a look at at it another way:

These types of planets are classified by composition as:

Gas giants (or gas dwarfs, depending on their mass) - planets composed primarily of hydrogen and helium. Includes Jupiter and Saturn.

Eccentric Jupiters are gas giants with orbits that are not circular. All non-circular orbits are considered “eccentric” and can either be elliptical, parabolic, or hyperbolic 

Hot Jupiters are one variety of gas giant that orbits close to the planet’s sun, causing the surface to be very high. These are close enough that their gases are being burned off, leaving a trail of material in their wake. Because of the required circumstances of forming a gas giant, they’re thought to have formed away from the star and migrated inward.

Hot Saturns are also called puffy planets, with densities similar or lower than Saturn but with an extra large radius.

Hot Neptunes are similar to the concept of Hot Jupiters in that they’re similar in mass to Neptune and Uranus and orbit close to their star.

Once these migrated gas giants--the Hot planets--have had their gaseous atmospheres stripped, their cores remain and they become Chthonian planets.

Ice giants - planets composed of substances heavier than hydrogen and helium, including water, methane, and ammonia. Includes Neptune and Uranus.

Terrestrial planets - planets composed of carbon, silicate, and/or metals, including: carbon planets, silicate planets, and iron planets according to what they’re made of. Includes all the inner planets: Mercury, Venus, Earth, and Mars.

The water planets mentioned in the above charts are considered a theoretical type of planet called an ocean planet. There’s also theoretical desert planets and lava planets depending on what their surfaces are comprised of.

Dwarf planets are a step below true “planet” in terms of labeling, and are characterized by the following: They orbit a sun, are not a moon, are nearly round in shape (which requires a certain level of mass), and, most importantly, have not cleared the debris from their orbit. Includes Pluto. (Of course, these days, dwarf planets orbiting our sun beyond Neptune are considered “plutoids,” but that’s just a nicety and wouldn’t apply to any dwarf planets outside our own solar system.)

Some other ways of classifying planets are names that apply specifically to our own solar system:

Exoplanets or extrasolar planets orbit other stars, but not our sun.

Extragalactic planets are outside the Milky Way.

Inferior planets orbit our sun within the Earth’s orbit.

Superior planets orbit out sun outside Earth’s orbit.

Inner planets orbit our sun within the asteroid belt.

Outer planets orbit our sun outside the asteroid belt.

Finally, you can also classify planets based on what they’re orbiting:

Circumbinary planets orbit two stars.

Double planets, or binary planets, are two planetary masses orbiting each other.

Pulsar planets orbit pulsars (rapidly rotating neutron stars).

Rogue or interstellar planets orbit the center of the galaxy, not a specific system’s star.

Next up: Orbits!

[theticklishpear]

(A table of contents is available. This series will remain open for additional posts and the table of contents up-to-date as new posts are added.)

Part Ten: How a Planet Gains Seasons & Plotting Environmental Zones

Each of the planets you choose to create will have some kind of temperature changes throughout their year, creating seasons. There are a couple of things that impact how seasons look on the planets, most importantly, the planet’s orbital eccentricity and its axial tilt.

Eccentricity:

First off, the seasons are not created by the Earth moving closer and further from the sun throughout its orbit, but the seasons are lengthened and shortened by it. The less eccentric (more circular) your planet’s orbit, the more regular the seasons will be; and the more eccentric (more elliptical), the more extreme the seasons. Remembering that planets orbit faster the closer to their sun they are, a planet with a higher eccentricity will have longer, more intense winters and shorter, more intense summers. With Earth’s orbit having an eccentricity of less than 0.05, the Earth’s seasons tend to be pretty similar in terms of length throughout the year.

Axial Tilt:

Planets rotate around a star in an orbit, but they also rotate as they go around that path. Stretching an imaginary piece of paper across the system from the star to the planet as it orbits is what’s called the orbital plane. The axial tilt is the angle at which the planet itself rotates within its own orbit in relation to that orbital plane:

Axial tilts can range from 0-180°. Planets with a prograde spin (spinning the same direction as their sun) will have axial tilts between 0-90°, and the sun will rise in the east and set in the west; while those with tilts from 90-180° spin retrograde (the opposite direction as their sun) and their sun will do the opposite.

Generally speaking, the planets with higher tilt:

are warmer,

have more extreme seasons,

have less snow and ice,

have lower humidity,

have less cloud cover,

and absorb more light than it reflects,

while planets with lower tilt exhibit the opposite properties.

Remember: If you want your planet to be habitable by humanoids, your axial tilt should be between 0-80° for prograde planets and 100-180° for retrograde planets! More severe tilts create more severe seasonal patterns that are likely to be unfriendly to humanoid creatures.

Tidally Locked Planets:

If your planet orbits as the same speed as its rotation, it’s possible for the planet to become tidally locked with its star. When this happens, the same side of the planet faces the sun the entire time it orbits the sun. This means that only part of the planet gets sun, making one side brutally hot and sun-scorched, and the other perpetually freezing and dark.

Environmental Zones:

Keeping in mind how you want your planet’s overall climate to be, the habitability, and what direction you’d like your sunrises and sunsets to be, you can pick any number in that 0-180° range. Once you’ve chosen your value, you can then start drawing out where the equatorial bands fall across your planet. Some values could give you some really wild and unexpected results, so I highly suggest drawing it out:

Start by drawing a circle to represent your planet, and divide that into four:

Next, draw a line at any angle within the limits outlined above:

Draw in your equator by putting in the perpendicular of the axial tilt you just drew in:

All the rest of the work will be based off this equatorial plane. Every planet will have 5 lines to draw in: the equator, the upper and lower edges of the tropics (on Earth, these are the Tropics of Cancer and Capricorn), and the upper and lower edges of the arctics (the Arctic Circle and the Antarctic Circle). The names of these limits will differ for any world you build. We’ve already got our Equator.

To find the limits of the tropics, draw a line parallel to your Equator both north and south that is the same number of degrees away as your planet’s axial tilt. (In this case, 14° North and South of my equatorial plane.)

Within the limits of the tropics, the sun will be directly overhead for at least one day of the planet’s year. Environments like rain forests and savannas, as well as monsoons are most likely to be found in these bounds.

Meanwhile, within the limits of the arctics, you’re looking at places more like tundra and ice, with at least one day per year of total darkness and one of total light.

To find those limits, draw a line parallel to your Equator both north and south that equals 90° minus your axial tilt. (In my case, 90°-14°=76°)

You can see that a planet like this, with a lower axial tilt, will have a broad area of temperate zones between the tropics and the poles, and then small arctic areas.

In a planet where the axial tilt is greater than 54°, the poles and the tropics switch places so that there is a band on ice and tundra around the center of the planet. Take a look at this planet made using exactly the same tactics as before:

Remember: The location of your axial tilt won’t change as the planet orbits its star, so once you have a basic understanding of kind of how the regions get plotted out on your planet based on its tilt, you can place that in its orbit around its sun and see how the sun’s light will hit it throughout its year.

You can imagine how my planet with the 14° tilt mostly keeps the same span of zones facing the sun as it orbits. This means that its seasonal changes won’t be as extreme, whereas with my 65° tilt, what portion of the planet’s zones face the sun changes drastically, making seasons extreme.

Next up: Days and nights!

[theticklishpear]

(A table of contents is available. This series will remain open for additional posts and the table of contents up-to-date as new posts are added.)

Part Four: The Birth of Planets

Last time, we talked about how when a nebula--a cloud of gas and dust in space--gets moving, the center starts to burn, thus birthing a star. While all that’s happening, the nebula is swirling, and in a way similar to how the air currents of your house push dust and particles together to form dust bunnies, so too do bits and pieces within the nebula start to bump into each other, forming globs that get bigger as they travel around the central star. And of course, as they get bigger, these clumps begin to weigh more, drawing in other clumps around it, and eventually you get the beginnings of a planet.

Now, if you might recall, the star at the center of the nebula is burning and what’s it’s fuel? Gas! Usually hydrogen. This, in addition to the heat being let off by the star, results in the center portions of the dust cloud to mostly be bits of rock and dust--the star has accumulated most of the gas around itself, and burned off any of the ice particles. Further out in the disc, however, the gases and ice chunks remain.

So as planets begin to form, generally the pattern that emerges is that the closer to the star a planet is, the more rocky it is, and the further out it is, the more gas and/or ice it’s likely to have. Not only that, but following the logic that the star has accumulated quite a bit already, the planets forming closer to the star have less to scoop up--less gases, less ice, just... less. So the planets forming in the outer portion of the nebula are more likely to be larger (not necessarily more weight, remember. A cloud is quite large, and paperclip isn’t, but the paperclip has more weight than the cloud; it is more massive.).

The Habitable Zone:

Now, assuming your star can exist long enough to life to develop on its planets, and assuming that we actually have any understanding of what’s required for life to exist, your planet needs to be in the Habitable Zone. We currently work under the assumption that habitability of a planet requires liquid water to be available year round. Whether that’s a truth for all life in the universe is a different question that I can’t answer, but for now, that’s our definition of a habitable planet. This also assumes that we’re talking about planets on which life develops on its own, rather than planets where life can be brought and find ways to exist.

The distance from the star at which liquid water is available for the duration of the planet’s orbit depends on the life stage of the star. Remember that older stars, burning red, are starting to exhaust their fuel supply. They burn cooler, so in order for a planet to stay within a comfortable range of the star where it would be neither too hot nor too cold, a planet would need to be closer than if it were orbiting a young, hot, bright star. Take a look:

In this diagram, you can see what I’m talking about. Earth sits comfortably within the habitable zone for our yellow sun, but when our sun begins to die, the habitable zone will shift.Venus and Mercury may eventually come to land smack-dab in the middle of that zone. If the star remains stable in that temperature/age range for long enough (billions of years), then it’s possible that the planet in the adjusted habitable zone, now that it has better conditions, might be able to spark its own life--maybe. Of course, the planet that was in the habitable zone before, has already died a painful and freezing death.

One more illustration. This one shows the habitable zone as the green ring, with blue being too cold and red being too warm.

What Does All This Mean For a Writer?

It’s unlikely that creatures or life forms would be able to evolve into anything on planets outside the habitable zone. Those places too close to and too far from the star aren’t going to be harboring life. Make sure that you’re placing your planet at an appropriate distance for the type of star you have. If your star is red, your planet needs to be closer, with the star large on the horizon. If your star is blue, your planet needs to be further out with the star smaller on the horizon.

One more thing, which is mostly hypothetical. Throughout the lifetime of your star, the planets that had life on them could conceivably have been farther from the star, with life possible on planets closer to the star as the star continues to age and cool off. Who cares, though, right?

Well, if your race is space-faring, there’s a possibility that remnants of life could be in evidence on planets further from the sun. Of course, this depends entirely on what kind of core the planet has and what “life” and “remnants of life” your characters are looking for. There’s not likely to be the foundations of houses on gaseous stars, since life forms of a gaseous star would need to exist in a very different way than, say, humans. But places like Mars, that used to be in the habitable zone and are also rocky places? Who knows. I’m just saying maybe, and if there were books written with that, I wouldn’t throw it out a window.

Next up: More than one star!