Saturday, September 29, 2018

The Long Dark - building a habitable planet

Almost a year ago, I talked about the unusual world setting of The Long Dark. This is a world with a roughly 90 degree axial tilt - so it’s effectively spinning on its side compared to the plane of its orbit.

The most obvious characteristic of such a world is its extreme seasons. Other than a narrow strip around the equator, everywhere will experience midnight sun and some day-long darkness. The closer you get to the poles, the longer those periods of perpetual day and night become.

The strangest points on the surface are the poles themselves. At midsummer, the sun will be stationary, directly overhead. Expect it to get very hot! As the days proceed, the sun will start to move in small circles, gradually getting wider and wider and closer to the horizon. When you reach the equinox, the sun will hug the horizon, then dip below, and you then have half a year of complete darkness. This is “the Long Dark” of the book’s title.

This extreme light/dark cycle was really the foundation for the story, but there are other important features I wanted to bring together, which meant some research to build a credible and consistent world.

When I first came up with the idea, I pictured the world circling a white dwarf. I don’t know why, but that was my mental image. As I developed the setting, though, I realized I wanted this world to have a very long year. I wanted my colonists to have several Earth years of “summer” in one hemisphere, before they had to migrate across the equator and set up camp in the other hemisphere.

This meant it had to be orbiting far out compared to Earth’s orbit, yet still warm enough at that distance to support liquid water and life. A white dwarf was not going to give me the conditions I needed.

I had an idea for how to resolve this, but no idea whether it was workable. I was delighted when some reading from a number of sources suggested I was on the right track.

In a few billion years, our own sun is expected to go through a red giant phase. It will expand to swallow the orbits of the inner planets, maybe even Earth’s. This led me to two very important realizations:

First, in this phase the “Goldilocks zone” will push outwards to cover the orbits of Jupiter and Saturn. The “Goldilocks zone” is what astronomers refer to as the habitable zone, where liquid water should be able to exist on a planet’s surface. Right now, anywhere beyond Mars is too cold, but when the sun expands, the frozen outer reaches of the solar system will get a lot more toasty.

The second note is that if this is the evolution of our sun, then a red giant like this must be roughly the same mass. This means planets’ orbital periods will be comparable to those of our own solar system for a given distance out. And somewhere around the orbit of Saturn gave me the length of year that I was aiming for!

Right there, I had a long orbit that lay in the habitable zone. My white dwarf became a red giant.

I’m sure there are other scenarios that would give me the right combination of conditions, but this one simply resonated with me. It also provided other useful features that I’ll talk about in future posts.

10 comments:

Susan Flett Swiderski said...

Methinks you have as much fun doing the research and figuring out how to attain a degree of realism in the worlds you create as you do in the writing itself. And it shows!

Alex J. Cavanaugh said...

Clever to consider what would happen with a red giant to our planets. Made your story much more possible.

Botanist said...

Susan, to be honest, I don't see much point in doing it in the first place if you're not having some fun at the same time.

Alex, that red giant phase was something I remembered. I'm happy that it proved to be useful.

Hilary Melton-Butcher said...

Hi ian - I know I 'missed' that post last year due to things overseas ... this year much the same - time will tell. It's amazing though how you've incorporated 21st century realisations into your world and added to your story as the scientists investigate this planet's end ... and early beginnings.

Can see why you're so involved ... take care and have a good week - let's hope the sun comes out again - cheers Hilary

David Batista said...

That's a great bit of world building you're doing there, Ian. This sounds like a really great setting for your WIP. Can't wait to read more!

Botanist said...

Hilary, I'm just happy those stray bits of knowledge happened to come together in the way I wanted them.

David, the setting is fun to work with. There's a lot more to come :)

dolorah said...

Nice! I like the Title, and the concept behind it. You've got some awesome planetary world building skills. Someday maybe you'll let me pick your brain for an Ice Planet I'm hoping to colonize.

Keep going Ian; you're rocking this world.

Crystal Collier said...

Love it! This is the kind of knowledge that makes me laugh at my middle grade fantasy in a world with three suns. Science is epic. I know this world would never work in reality, but it's still fun to write.

Botanist said...

Donna, you are welcome to discuss worldbuilding any time. Just drop me a note through my contact page to get in touch.

Crystal, one of these days I'll have to look into the mechanics of a three-sun system. I know multiple suns is a favorite sf staple, but I wonder how hospitable any planets in such a system would be.

Lynda R Young as Elle Cardy said...

The Three-Body Problem by Liu Cixin covers such a world with three suns. It's an interesting book--as is your world-building.

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