Sci-Fi World-building: Mars the farm planet?

[Irish Wolf]

You're also going to need to import fertilizer. A lot of fertilizer, at least at first (human waste is too high in potential pathogens to use without at least a year of processing, and then you have to overcome the "yuck" factor in the market). Nothing's lived and died on Mars recently enough to provide the soil, such as it is, with nutrients.

[whswhs]

Originally Posted by Irish Wolf

You're also going to need to import fertilizer. A lot of fertilizer, at least at first (human waste is too high in potential pathogens to use without at least a year of processing, and then you have to overcome the "yuck" factor in the market). Nothing's lived and died on Mars recently enough to provide the soil, such as it is, with nutrients.

Heinlein gave a detailed explanation of this in Farmer in the Sky. It was the first place I learned about the difference between soil and regolith, long before I ever heard the latter word (Merriam Webster says it was coined in 1897, but Heinlein didn't use it).

[Agemegos]

Originally Posted by whswhs

Heinlein gave a detailed explanation of this in Farmer in the Sky. It was the first place I learned about the difference between soil and regolith, long before I ever heard the latter word (Merriam Webster says it was coined in 1897, but Heinlein didn't use it).

Another good word for people who are considering terraformation is "pedogenesis", referring to the formation and origins of soil. It's complicated, and takes time: pedologists estimate the natural rate of soil production at about 0.000 1 metres of topsoil per year. Perhaps futuristic biome engineering, enhanced perhaps with designer organisms, can do better. Still, you have to reckon that it will take on the order of centuries to create topsoil.

Engineering pedogenesis over millions of square kilometres is a daunting prospect; I can't doubt that it will be done by the scheduled introduction of different successions of species in various environments, making up self-extending successions of biomes, spreading as blotches with pioneer species at the edges and climax biomes in the centres. The leading edge of a bullseye biome will consist of hardy bacteria, algae, and lichens capable of colonising abiotic regolith and modulating its weathering, then you want higher plants to shelter the surface and limit erosion while fixing carbon and nitrogen in the primitive soil. Then animals as efficient pollinators and dispersers of the larger seeds, as autotrophs to accelerate the production of humus, and as bioturbators to carry organic material down into the lower soil horizons. Early stages can perhaps be effected by dispersing spores in high-level winds, but the later organisms will have to be placed more directly and carefully.

The direct production of soil by mechanically ploughing a succession of ever less hardy and more productive fallow crops into the regolith would be quicker, but only affordable on a small scale. Pioneering settlements my be supported on such farms, and they may be built as nurseries; the planet will be terraformed by ecosystem engineering.

[Agemegos]

Originally Posted by Prince Charon

One advantage to exporting anything from Mars is that the gravity is lower than Earths, so even with the super-cheap torch drives, liftoff from Mars will still be much cheaper than liftoff from Earth.

Yes. That suggests that food and other agricultural products from Mars will be particularly competitive with alternative supplies from Earth for consumers in space, including those in Earth orbit.

[Michael Thayne]

Water and fertilizer are clearly real concerns, but I don't feel too bad about taking them for granted. I should maybe double-check this assumption but my impression is that getting enough water from ice asteroids would not be the hardest part of Mars terraforming by any stretch. And since food is relatively low value per weight, freighters returning from Earth to Mars with manufactured goods will probably have lots of space capacity to use transporting fertilizer.

However, my impression is that attempted simulations of farming on Mars have had success growing food in questionable soil (say volcanic ash and fertilizer) and lower-than-normal lighting conditions. Maybe the experiments are bunk but NASA seems to take them seriously. So I'm inclined to think those are lesser concerns?

[Bengt]

You'll need to bioengineer plants that can grow in a low oxygen atmosphere. While earth plants do produce excess oxygen they still use atmospheric oxygen for their cellular respiration and anything evolved on earth expect a certain oxygen pressure. I'm assuming you didn't want to grow all this food in pressurised chambers.

[Michael Thayne]

Many proposals for terraforming Mars involve using algae to get the oxygen-producing process going. Apparently algae are extremophiles? With enough water to get oceans on 1/3 of Mars or more (anyone have a reference for how much water that is?), and no marine animals eating the algae, it seems like you could get oceans absolutely thick with algae relatively easily. Then trawlers could scoop it up. So perhaps algaculture would be a viable industry. Thoughts?

[Fred Brackin]

Originally Posted by Michael Thayne

However, my impression is that attempted simulations of farming on Mars have had success growing food in questionable soil (say volcanic ash and fertilizer) and lower-than-normal lighting conditions. Maybe the experiments are bunk but NASA seems to take them seriously. So I'm inclined to think those are lesser concerns?

Without wading through a scientific paper I would wager that the authors would be trying to advocate that the possibility is "enough" for self-support under certain circumstances. After all, they aren't anticipating a^ torch drive to make shipping supplies from Earth even possible for any sort of price much less cheap. They only need for Mars-grown stuff to be cheaper than what you can ship from Earth with hard science drives.

There is no way that putting only 40% of the energy into the front end of the process is going to a "lesser" issue when doing the economics. Besides you need to warm Mars some way. Giant mirrors would kill two birds with one stone.

[ericthered]

Originally Posted by Michael Thayne

Many proposals for terraforming Mars involve using algae to get the oxygen-producing process going. Apparently algae are extremophiles? With enough water to get oceans on 1/3 of Mars or more (anyone have a reference for how much water that is?), and no marine animals eating the algae, it seems like you could get oceans absolutely thick with algae relatively easily. Then trawlers could scoop it up. So perhaps algaculture would be a viable industry. Thoughts?

I'm not sure you'd want to feed the result to humans. However, I suspect something like pigs or farmed fish would gobble it up with gusto. This also means your final product has a higher value density than grain, which is nice for transportation.

Algae is an extremely broad term that includes multiple clades of organism and in its broadest sense (and use as a terraforming tool is one case where it actually applies) crosses the border of broad domains of life. So yes, extremophile algae exist. And terraforming probably involves genetically engineering some to tailor fit your target planet.

[AlexanderHowl]

Your main issues are nitrogen and water. Everything living requires nitrogen, and Mars practically has no nitrogen and very little water. In order to create 1 atmospheric pressure, you would require the equivalent of two Earth atmospheres worth of nitrogen (around 10 quadrillion metric tons). The nearest sources of massive quantities of free nitrogen are Earth (~0.8 atmospheric masses), Venus (~4 atmospheric masses), Titan (~4 atmospheric masses).

As for water, you would need a minimum of 10 quadrillion tons of water to make Mars as habitable as the Atacama Desert, and a minimum of 100 quadrillion tons of water to attempt any massive agriculture for local support. Anything less, and the atmosphere will just suck up the water.

So, we are talking about a minimum of 110 quadrillion metric tons of nitrogen and water. Now, you can produce oxygen locally, so you could reduce that to around 21 quadrillion metric tons, but you would need a way to transport the hydrogen (ammonia would be a partial solution, but 10 quadrillion tons of hydrogen can only transport ~2 quadrillion tons of hydrogen).

But wait, there is more. Every kilogram of matter traveling from LMO to Mars surface possesses ~10 MJ of energy, meaning that 21 quadrillion metric tons generates 210 YJ of energy. Mars only receives around 25 PJ/s, so the energy from transporting the necessary materials to Mars would be equal to 8.4 billion seconds of sunlight, around 250 Earth-years. To avoid boiling off everything, you would probably need to spend 1000 Earth-years just dropping stuff onto Mars.