Steve Jackson Games Forums Sci-Fi World-building: Mars the farm planet?
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01-22-2020, 11:40 PM   #21
Michael Thayne

Join Date: May 2010
Re: Sci-Fi World-building: Mars the farm planet?

Quote:
 Originally Posted by 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.
I think some of your math might be wrong. According to this NASA fact sheet, the current mass of Mars' atmosphere is only 25 trillion metric tons. I might be wrong about this, but I thought the relationship between atmosphere mass and atmospheric pressure was linear?

 01-23-2020, 12:00 AM #22 Michael Thayne     Join Date: May 2010 Re: Sci-Fi World-building: Mars the farm planet? Also, could some plants—perhaps genetically engineered ones—survive in a mostly-CO2 atmosphere derived from melting Mars' (dry) ice caps?
01-23-2020, 01:07 AM   #23
Bengt

Join Date: Oct 2005
Location: Ronneby, Sweden
Re: Sci-Fi World-building: Mars the farm planet?

Quote:
 Originally Posted by Michael Thayne Also, could some plants—perhaps genetically engineered ones—survive in a mostly-CO2 atmosphere derived from melting Mars' (dry) ice caps?
GEd single cell organisms is more plausible. We already have some living in pretty weird places to work with.

01-23-2020, 08:41 AM   #24
ericthered
Hero of Democracy

Join Date: Mar 2012
Location: far from the ocean
Re: Sci-Fi World-building: Mars the farm planet?

Quote:
 Originally Posted by AlexanderHowl Your main issues are nitrogen and water.
On the amount of nitrogen, you "only" need about 60% of an earth atmosphere. You've got to stack twice and a half as much on any given spot, but mars has about a quarter of the surface area as earth.

But that's not a farming problem, that's a terraforming problem, and some neo-emperor or the other already spent the stupid amount of money to get you there. You've on a planet mostly terraformed but with too much CO2 where mars is, how do you profit off the former crazy whale's extravagance?
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 01-24-2020, 01:52 AM #25 Bengt     Join Date: Oct 2005 Location: Ronneby, Sweden Re: Sci-Fi World-building: Mars the farm planet? If you have liquid surface water in a mostly CO2 atmosphere it will have significantly lower pH than on earth as the CO2 dissolves and form carbonic acid. Don't know what pH will be when the oceans are saturated as what I've read is about earth with 0.04% CO2.
 01-24-2020, 05:30 AM #26 Anders     Join Date: Jan 2005 Location: Gothenburg, Sweden Re: Sci-Fi World-building: Mars the farm planet? It depends on the partial pressure of CO2 and the temperature. There's a table here: https://en.wikipedia.org/wiki/Carbonic_acid But genetic engineering can probably overcome the pH problem. __________________ “He who knows only his own side of the case knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side, if he does not so much as know what they are, he has no ground for preferring either opinion... Nor is it enough that he should hear the opinions of adversaries from his own teachers, presented as they state them, and accompanied by what they offer as refutations. He must be able to hear them from persons who actually believe them...he must know them in their most plausible and persuasive form.”
01-24-2020, 11:35 AM   #27
Daigoro

Join Date: Dec 2006
Re: Sci-Fi World-building: Mars the farm planet?

Quote:
 Originally Posted by Agemegos Still, you have to reckon that it will take on the order of centuries to create topsoil.
I'm not sure it needs that long. Volcanic lava flows can become vegetated in a matter of years or decades. They do have the advantage of having biotic material carried in from neighbouring regions, but they still develop a sustaining soil fairly quickly.

Source: My visit to Sakurajima volcano, and a tourist sign showing a diagram of revegetation. 30 years for grasses to colonise bare rock, 80 years for low shrubs, 100 years for tall trees, 200+ years for so-called "climax forest" (mature, steady state growth).
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Last edited by Daigoro; 01-24-2020 at 11:54 AM.

01-24-2020, 03:17 PM   #28
Agemegos

Join Date: May 2005
Location: Oz
Re: Sci-Fi World-building: Mars the farm planet?

Quote:
 Originally Posted by Daigoro I'm not sure it needs that long. Volcanic lava flows can become vegetated in a matter of years or decades. They do have the advantage of having biotic material carried in from neighbouring regions, but they still develop a sustaining soil fairly quickly. Source: My visit to Sakurajima volcano, and a tourist sign showing a diagram of revegetation. 30 years for grasses to colonise bare rock, 80 years for low shrubs, 100 years for tall trees, 200+ years for so-called "climax forest" (mature, steady state growth).
Around here a lot of spotted-gum forest grows on poor shale country where there isn't enough topsoil to grow crops. (Where the soil is eighteen metres deep the land has been cleared for farming.) Trees will grow to considerable heights in ground you couldn't possibly draw a plough through or pick a potato from if one grew, and put down deep roots in freely-draining material that won't retain moisture in the root zone of grasses and herbaceous crops.

You can grow plants in sand or vermiculite if you pour on enough water and fertilisers, but you have to keep them out of the rain. That's essentially hydroponics, not agriculture.

Of course futuristic designer crops could well be deep-rooted perennials that you run a header over but don't plough in and re-plant over.
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Last edited by Agemegos; 01-24-2020 at 03:43 PM.

01-26-2020, 06:13 PM   #29
Michael Thayne

Join Date: May 2010
Re: Sci-Fi World-building: Mars the farm planet?

Quote:
 Originally Posted by AlexanderHowl 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.
Thinking about this more, I wonder if it's more complicated than that. Sure you might need 100 quadrillion tons to get significant ocean coverage on Mars, but less isn't going to produce a uniform desert—I suspect 10s or 100s of trillions of tons of water would be enough for small seas / lakes here and there? Might be wrong about the dynamics of it tough.

 02-12-2020, 09:57 AM #30 hcobb     Join Date: Aug 2004 Location: Pacheco, California Re: Sci-Fi World-building: Mars the farm planet? The why is simple. Somebody nukes Morocco and Earth no longer grows food. https://en.wikipedia.org/wiki/Peak_phosphorus __________________ -HJC

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