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.