Writing a convincing planet

NASA: D. Aguilar/Harvard-Smithsonian Center for Astrophysics

Donna's post last week about weather in SF prompted a bit of thinking on my part. Some of the comments on that post made some great points, about artificial 'climate' in space. Quite a few authors have included virtual environments in spaceships in their stories. Jack McDevitt and Elizabeth Moon both come to mind. I'd never thought about it from the point of view on mental stability, but given that we humans are such fragile creatures, very much governed by the circumstances in which we developed, it makes a lot of sense.

However, events on other planets involve much more than weather. It's much easier for we authors to accept without further comment that planets have much the same gravity as Earth, that the atmosphere is breathable, that the light quality is the same. But that's not very likely to be the case unless planets are terraformed. Elizabeth Moon uses that approach and McDevitt does, too – although not for all worlds. Even if we do terraform, it won't change everything.

Let's say we terraform Mars. The sunlight is the same, the length of day is pretty much the same. Since we've terraformed, we can grow Earth plants and animals. But years are much longer. Plants would have to adapt to a much different growing cycle, or be grown in artificial conditions. I expect a bit of genetic engineering might have to be used. Then there's the gravity. Mars is half the size of Earth. Gravitational pull weakens by the radius squared. So let’s say you weighed 60kg on planet Earth. You'd weigh 22.3kg on Mars. (Find out more about weight on other planets here. http://gretavanderrol.net/2012/11/25/what-would-you-weigh-on-an-exoplanet/ Fascinating stuff.) People will grow taller, they won't be as physically strong (because they don't have to be) and certainly new arrivals will be much stronger than the locals. See John Carter. The movie was pretty accurate in that respect.

On other planets conditions could be very different. There may be no axial tilt, therefore no seasons. There may be no polar icecap. Earth didn't have a polar icecap many times. On the other hand, the world might be freezing, undergoing an ice age. (But even during our worst ice ages, the equator wasn't ice-bound.) Even if we assume the planet has a breathable atmosphere, the parts where people can live might be very different. A belt around the equator for a cool world with no axial tilt, the poles for baking hot worlds. Sea islands for hot worlds.

Then there's the sun itself. Most stars in the galaxy are red dwarfs, smaller, cooler and slower burning than our sun. So the planet would probably be closer to its primary, and the light would be different. I tried to show that difference in the first Iron Admiral book. Here's the section where Allysha arrives at Tisyphor.

Good grief, it was like walking into a sauna. She hesitated until Sean’s hand on her back urged her forward. Moisture began to bead on her face, her shirt stuck to her skin and she was certain she could feel her hair begin to curl. The air tasted different, too; a little bit earthy and sweet. Not unpleasant; just not what she was used to and different again to the arid, dusty air of Brjyl, the only other planet she’d been to apart from home.

The ship had landed on a platform above purple and green forest that spread to the horizon on three sides. Blues and greens seemed brighter, somehow, and reds and oranges more subdued.

Earth also has an enormous moon (when considered as a percentage of Earth) – to the extent that Earth can be seen as a double planet system, a bit like Pluto and Charon. So we have bright nights at full moon, and large tidal flows. If a planet has two small moons, like Mars, they won't have anywhere near the tidal effects and won't throw off anywhere near as much light. Small details which can be slipped into stories to make them that little bit more 'real'.

There are so many variations possible on faraway planets that it's impossible to consider them all in this little post, and some variations add complexity to the story that don't really help the plot. But it's worth bearing in mind that exo-planets are not Earth. Adding those little details may be just what's needed – especially if you throw in a bit of weather.

Will humans populate the exo-planets?

The more I read about the strangeness of our universe, the more I wonder if humanity will ever colonize other planets. There's not much chance we'll settle on a diamond planet and I have to wonder how we'd go on many of the 'earthlike' planets already pinpointed. We are such fragile entities, we humans.

Like all other animals we are closely attuned to our environment, more so than many of us realize anymore. In these days of electricity we can heat or cool our homes, spend half the night watching TV or reading books, source food from all over the world so nothing is ever out of season, cross distances that took years in days. Yet we cannot escape the environment which shaped us.

I think there are five vital factors we will not easily overcome.

Time

Time is relative. When it's 8am on a Thursday where I live, it's 6pm the previous day in New York. Yet it's the same 'time'. However, the elements that we use to measure time have a profound impact on our bodies. By that I mean the rotation of our planet, and its orbit around the sun. Whether we think the sun is rising where we are, or setting, our bodies are built to expect a 'day' of twenty-four hours or so, because that's how long it takes the Earth to revolve on its axis. What's more, if we are suddenly wrenched from one time of day to another, as happens with long distance air travel, it takes time for our bodies to adjust. (It's called jet lag.)

Gravity

We have evolved to suit the amount of force the planet exerts upon is. The advent of space travel and weightlessness has proved how important gravity is to our ability to function. Without gravity our bones lose density and muscles atrophy. Returning astronauts struggle to rebuild their bodies. In science fiction space ships have ways of providing gravity, either by centrifugal force, like the rotating space station in 2001: a Space Odyssey, or via an unspecified means of creating artificial gravity, found in Star Wars, Star Trek and the like. Long periods on a planet with low gravity is sure to have similar effects. Mars and the Moon are obvious examples. Sure, you can bounce around. But what happens if you come back to Earth? Or move on to another planet with much stronger gravity than Earth?

Atmosphere

Most of our atmosphere is nitrogen, with twenty-three percent oxygen and a bunch of other gases in smaller quantities, including carbon dioxide. It also has a level of density. There's more of it at lower altitude (see gravity). See what happens to mountain climbers if they climb before becoming acclimatised. Their bodies can't cope. And if that mixture of gases changes past a certain level of tolerance, then what? Sure, we can wear space suits. But that's not ideal if you're colonizing a new planet.

Temperature

Humans exist in an apparently wide range of climates, providing they can find protection from the elements. But the range is actually not that wide in the scheme of things. This article in New Scientist speculates that global warming of only about 11° would render many places on our own planet 'unlivable'.

Light

Earth orbits a G class star which emits light towards the red end of the spectrum. We're used to seeing colors in that light. If we lived on a world orbiting a cooler star with redder light, or a brighter star with more bluish light, we'd see colors differently. For example, with light from a red star, blues and greens would be brighter, and reds and oranges more subdued.

Humans are adaptable. That's why the species has been so successful. But even so, we've only ever had to adapt to the extremes of one planet. If humans are to venture to other planets I believe we will have two choices; terraform the planet into another Earth or modify the settlers to cope with the conditions. That would mean physically very different races of humanity occupying different planets.

And here again, SF can offer plenty of examples. Elizabeth Moon's Serrano series has terraformed planets, as does Jack McDevitt's universe in Slow Lightning. A different approach is taken in Moon and McCaffrey's joint effort, Sassinak, where members of the Star Fleet have different body characteristics, depending on which planet they come from.

I admit I don't take that route in my own writing. Like the Star Treks and Star Wars of this world, I simply assume all planets are earthlike, with only small variations in light, heat, time and gravity. I reckon I'm in pretty good company. Come on SF fans and writers, what do you do, what do you prefer? Can you think of other limiting factors? Or do you think I'm pessimistic?