D-10: The Cloud World

The following was originally published on the Stellaris forums. No pictures today, sadly.


Once again, a big thank you to Admiral Howe for terrifying us with an explanation of how safe it is to stay on Earth. He’ll be back next week to share more knowledge.

Let’s talk about a planet that we might flee to if and when the Siberian Traps recur and all multi-cellular life needs to find a new home. (Good luck, archaea! Let us know how it turns out!) We’re going to discuss Kepler 442b.

You know the drill by now: first we ask what the star is like. Kepler 442 is K-class, which means she’s orange and slightly smaller than the Sun. Through an Earthlike atmosphere her light would look yellow and there’d be about two-thirds as much of it. We’ve seen worse: Gliese 667Cc, for example, only gets reddish light at 20% of Earth levels. Kepler 442 is, however, quite metal-poor. Because planets and stars are normally formed from the same material, this means that the planets in the Kepler 442 system would be too.

Kepler 442b is a little larger and a little heavier than Earth. The extra size helps to offset the increased pull of gravity, meaning that if you stood on her surface you’d probably only feel 30% heavier.

(We cover a lot of larger-than-Earth planets on the astroknowledge series. This is because they’re easier to spot. There are probably lots of smaller-than-Earth planets too, but we haven’t found them yet.)

I’ll come out and say it directly: unless she had a thick atmosphere, Kepler 442b would be cold. Her surface temperature on the equator during the day would be 233K, which is -40C. However, if she had a thicker atmosphere then she could retain much of this heat and nurture a greenhouse effect.

Too much greenhouse effect, of course, is a bad thing. It’s all about balance.

Greenhouse effects are caused by triatomic gases in the atmosphere: that is, gases which have three atoms per molecule. While there are many gases which are triatomic, the most famous and probably most important are carbon dioxide and water vapour. Climate scientists have modelled atmospheric carbon dioxide extensively, and we’re just starting to learn about what water vapour does in the atmosphere. While it’s not my field, it’s my understanding that water vapour is much better at causing a greenhouse effect than carbon dioxide is.

However, if the planet is below 0 C, there’s going to be no water vapour in the atmosphere because it would be frozen. This means that we’ll need enough carbon dioxide to get the greenhouse started and get the temperature above 0 C, at which point water vapour can start to amplify the process.

In other words, if Kepler 442b doesn’t have enough carbon dioxide then she’ll be an arctic planet. If she does have enough, however, then she could be quite warm.

How warm?

Answer: pleasantly, the answer is “not too warm.” As water vapour increases in the atmosphere it forms clouds. Clouds are white [citation needed.] White things reflect heat. Therefore, the hotter the planet gets the more clouds it has and the more of Kepler 442’s light it reflects away. We call this albedo.

James Lovelock pointed out that this creates a self-balancing system: a hotter planet has more clouds and so has a higher albedo, which means it receives less light and so cools. A cooler planet has a lower albedo, so it receives more light and so warms up. He then got very weird and mystical about it but the principle itself is sound.

If Kepler 442b has a greenhouse effect dominated by water vapour (like Earth does) then her temperature will stabilise between 0 C and 100 C, which is good news because that’s what humans find comfortable.

Considering Kepler 442b’s higher gravity, her atmosphere will be denser than Earth’s, which means that she may well be more humid. This, in turn, means that where Earth has deserts she’ll have jungles, and where Earth has plains she’ll have swamps and forests. Plant life loves humidity, and even if it isn’t hotter it feels hotter and more unpleasant.

What would it be like to live there?

The very densest forests are the sort known as cloud forests: they grow where the air is saturated with water, so that plants can feed directly from it rather than needing deep roots. In the cloud forests, trees grow to immense heights and are covered with secondary vegetation. The humid air of Kepler 442b might lead to this being common.

Innately fertile regions often have extremely fragmented government. If every glade can fend for itself without the help of the next, and if it’s possible to escape a lord’s rule simply by moving elsewhere, then the lord has less ability to enforce their will on the people. In historical Europe, lords tried many elaborate schemes to prevent people “voting with their feet” in this way, from serfdom to border controls, but none of it worked very well. Society naturally fragments into lots of little states, each with their own unique slant on government, philosophy and religion.

Humid, fertile regions are also cauldrons of disease. This would encourage primitive peoples to spread out rather than concentrating in any one region, and so would naturally limit the size of cities.

Both of these factors can be overcome with technology, of course, but their effects upon culture would linger. The people of Kepler 442b might grow up suspicious of foreigners, taking pride in their petty differences, and fearful of unified government. When they went into space this might cause a profound dislike of aliens, but also an attitude to space colonisation as being less about spreading their culture than about creating new cultures. They wouldn’t have colonies so much as alternate home planets, owing little allegiance to Kepler 442b itself.


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