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In this answer to the question "What would the full hypothetical Mars terraforming roadmap look like ?" there's a link to the article "Zubrin on Terraforming Mars" in Universe Today,
From an interview with Robert Zubrin in that article:

RZ: If one considers the problem of terraforming Mars from the point of view of current technology, the scenario looks like this:

  1. A century to settle Mars and create a substantial local industrial capability and population.
  2. A half century producing fluorocarbon gases (like CF4) to warm the planet by ~10 C.

(Emphasis by me)

Part of the main question is: did he sufficiently take into account the extremely large amount of rock that needs to be excavated and processed to extract the required amount of Fluorine ?

The MSL rover Curiosity detected fluorine containing minerals in Gale crater.

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    $\begingroup$ The Case For Mars is probably the most detailed version that Zubrin has published. $\endgroup$ May 30, 2021 at 16:35
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    $\begingroup$ Note that part 2 follows part 1, developing "substantial local industrial capability". So it seems reasonable to assume that he was indeed taking this into account. $\endgroup$ May 30, 2021 at 17:50
  • $\begingroup$ @Andrew Indeed, thank you. I've added "sufficiently". $\endgroup$
    – Cornelis
    May 30, 2021 at 19:45

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I find Zubrin frustrating because he doesn't reference the material he includes in The Case for Mars, even though the science is almost entirely other people's work. (I was an acolyte and have an autographed copy of TCFM).

Andrew's answer is good, so I'll just add of few insights of my own.

Adding fluorocarbons to Mars atmosphere was first suggested by James Lovelock in his 1984 sci-fi novel The Greening of Mars, where he envisioned importing the stuff.

Chris McKay et al were the first to give the idea scientific credibility in a 1991 Nature review article. Then they estimated ~${10}^8$ tonnes/year continuous production would be required to achieve 0.01 mbar at steady state ~ 250 times Zubrin's 0.04 microbar in Table 9.2 p266 of TCFM. As per Andrew, Zubrin estimates 880 t/hr production with 4,490 MWe power requirement.

Marinova and McKay (him again) estimate that ~0.1 Pa (1 microbar, or twice that to achieve a runaway greenhouse effect, since shown to be highly dubious) of the "best combination" of ${CF_4}$, ${C_2F_6}$, ${C_3F_8}$ and ${SF_4}$ would achieve $\Delta$T of +12.3 K. I estimate this to be a mass of ~5 billion tonnes. If we assume a long atmospheric half life which seems reasonable, the production of ~100 million t/yr over 50 years is required to meet Zubrin's timetable, at a bit more than 10,000 t/hr. At this point Zubrin is about an order of magnitude out. But the magnitude of the task is not unreasonable. Global steel production is about twenty times this.

Over 50 years more than 30 tonnes of fluorine per km^2 of Mars surface is required. Martian regolith has between 0.8% and 2.2% fluorine by weight, mostly as fluorite (CaF2), much higher than the concentration in Earth's crust of 600-800 ppm.

Currently I can find no research on the manufacture of fluorocarbons on Mars. On Earth they are made almost entirely from acidspar, which is at least 97% ${CaF_2}$.

If we assume pure calcite is available (${CaF_2}$) and ${CO_2}$ at one atmosphere pressure (95% of the atmosphere of Mars is ${CO_2}$, but only at a pressure of 0.006 atm, but it's very easy to pressurise, so no problem here), we can estimate the minimum energy required to form ${CF_4}$ using Hess's Law. The overall equation is:

${2CaF_2} + {CO_2} => {CF_4} + {2CaO}$

This is an endothermic reaction requiring +646 kJ/mol of ${CF_4}$ produced, or 7 MJ/kg of ${CF_4}$.

For Zubrin's 880 t/hr or 240 kg/s that's ~1,700 MWe. For 10,000 t/hr it's about 20,000 MWe.

That's the bare minimum. This excludes consideration of the following:

  • pure calcite is unlikely to be found, but experience on Earth with Acidspar suggests near pure deposits are likely. But how abundant?
  • energy will be required to clear any overburden and transport the ore
  • energy will be needed to purify the ore to near 100% calcite. This may involve dissolving impurities, but the solute would be recycled.
  • carbon dioxide must be pressurised, which takes energy
  • The analysis ignores questions of activation energies & reaction rates (kinetics). The reaction vessel will require heating, which will result in heat loss & hence inefficiency. The greater the activation energy, the higher the temperature, and the greater the inefficiency.
  • fluorocarbons are currently made from hydrofluoric acid, which is first produced from ${CaF_2}$. Given ${CO_2}$ is cheap, that suggests the above process is infeasible. None-the-less it sets a minimum energy requirement.
  • electricity generation is never 100% efficient.

I must have left something out!

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    $\begingroup$ Thank you for this extensive answer ! Let's face reality, this is not gonna happen within a thousand years, if ever ! I think a more real option would be the use of a huge inflatable, transparant, dome-shaped structure that would have to be more or less airtight where it meets the surface. If this dome would be situated within Gale crater, the escaping greenhouse gas could stay within the crater long enough to cause a considerable raise in the temperature there. $\endgroup$
    – Cornelis
    Apr 5 at 9:40
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    $\begingroup$ @Cornelis The more I look into it the worse it gets. This reaction, 2CaF2 + CO2 -> CF4 + 2CaO Is not done or Earth either because it's impossible or ridiculously hard. True, fluorite (CaF2) is the source of almost all the world's fluorine. The first step is always the reaction of fluorite and concentrated sulfuric acid, producing hydrofluoric acid. CaF2 + H2SO4 → 2 HF + CaSO4 So that means a vast amount of sulphur is required on Mars and a vast amount of CaSO4 is produced as waste. After HF, several paths exist for making fluorocarbons, but they're complicated. $\endgroup$
    – Galerita
    Apr 6 at 2:24
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I dug out The Case For Mars (1997) and while it gives some very basic outlines of this, it does not go into any great detail. From Chapter 9:

The industrial effort associated with such a power level would be substantial, producing about a trainload of refined material every day and requiring the support of several thousand workers on the Martian surface. Power levels of about 5000 MWe might be needed, which is about as much power as is required today by a large American city such as Chicago. A total project budget of several hundred billion dollars might well be required. Nevertheless, all things considered, such an operation is hardly likely to be beyond the capabilities of the mid-twenty-fist century.

These calculations in the book are based on producing enough CFCs (probably CF4) to raise the global temperature by around 10K, which he calculates as 0.04 microbar of CFCs, needing about 880 tonnes/hour for twenty years, and an ongoing production rate of about a fifth of that to maintain it once it's built up.

He does not specifically discuss the mining infrastructure needed to get the fluorine, but as it's talking about thousands of workers and city-scale power requirements, it's clear he's aware of how substantial a project it would be.

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    $\begingroup$ Query: When the authors mentions years, is that Earth years or Martian years? There's a big difference. $\endgroup$
    – Fred
    May 31, 2021 at 16:07
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    $\begingroup$ @Fred aha, I've just noticed the previous table in this chapter explicitly says "Earth years"; I think we can probably guess that is the time units being used throughout. $\endgroup$ May 31, 2021 at 18:17
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    $\begingroup$ @Cornelis The model he's using is described in the chapter, but the specific calculation for CFCs isn't given (it's dealt with in about a page, as one of several options). $\endgroup$ May 31, 2021 at 18:20
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    $\begingroup$ "such an operation is hardly likely to be beyond the capabilities of the mid-twenty-fist century." I just hate handwavium. $\endgroup$
    – RonJohn
    Jun 1, 2021 at 4:57
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    $\begingroup$ @Cornelis: CF4 is an aggressive greenhouse gas (much more aggressive than CO2). But to get reasonable estimates of warming you need a proper atmospheric model complete with lapse rates for both temperature & pressure: simple-minded single-layer models don't work, at all. Given known lapse rates it is possible to hand-crank such a calculation as Arrhenius did to get quantatively-OK estimates, or to run a very trivialised computer model. That might be good enough on Mars as there's not much water in the atmosphere. $\endgroup$
    – user21103
    Jun 1, 2021 at 9:36

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