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In the year 2099 A.D, humans made a major discovery. There is a rich source of fossil fuel buried beneath layers of Martian soil. It is estimated that the coal deposit that was discovered could fill as much as 1 billion barrels of oil and there are probably more to be discovered.

While it is tempting to set them ablaze in a controlled setup, will people use them as their main source of fuel or there are better alternatives?

Assume there was life in the early history of the red planet long before we colonized it.

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  • $\begingroup$ This book is related, I've not actually read it but it contains an academic analysis of the costs and possibilities for energy sources on mars and transportation costs: books.google.co.uk/… $\endgroup$
    – Tim B
    Aug 26, 2015 at 9:27
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    $\begingroup$ If we have the technology to reliably get to Mars and mine it, it isn't too much of a stretch to assume we'd have a much more reliable fuel source like fusion. I'd just go with that and ignore all that coal, especially considering the extraction cost. $\endgroup$
    – Shollus
    Aug 26, 2015 at 13:02
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    $\begingroup$ A billion barrels is close to zero on earth where 100 million per day of oil is consumed. So, with the lack of oxygen, it would have to be terraformed, and if it is terraformed, then it has a huge population which already gets their power elsewhere... $\endgroup$
    – MikeP
    Aug 24, 2016 at 16:26
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    $\begingroup$ As an aside, I'm fairly sure coal deposits would be strong evidence for abundant life in the planet's past. $\endgroup$
    – Emilio M Bumachar
    Jun 29, 2019 at 10:48
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    $\begingroup$ If your Mars contains coal deposits, then you need a new map, you ended up on not Mars. Regardless, you now have a pile of carbon. What are you going to do with it, burn it in CO2 near-vacuum? The oxygen concentration on Mars is 1/28000th as high as on Earth. You might find this grossly inadequate for combustion. $\endgroup$
    – PcMan
    Feb 23, 2021 at 23:20

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Burning fossil fuels on Mars is highly impractical. Burning coal means using up oxygen, which is not readily available on Mars. As long as the human population on Mars has to live in environmentally closed colonies, Oxygen has to be produced by cultivated plants through photosynthesis, liberated from water or minerals at prohibitive energy cost (more energy than you could get from burning coal), or even imported from Earth. As long as Mars is not terraformed and therefore not producing a large surplus of oxygen through photosynthesis, coal or other fossil fuels are not an economical option for energy generation.

If and when Mars has been terraformed into something resembling Earth, burning fossil fuels is just as viable as on Earth. However, by that time the technological and scientific state of the art must have advanced so much that burning coal for heat is most likely obsolete anyway.

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  • $\begingroup$ the coal may be interesting as an entrypoint to chemical synthesis though - it will save energy for reaction paths that end in something organic; So the coal may not be of use as an energy source per se, but may be considered an energy saver in the otherwise solar/nuclear powered synthesis industry that will otherwise have to rely on carbon-source material imported from earth or very energy-intensively freed carbon from mineral deposits that bind C much harder than coal. $\endgroup$
    – bukwyrm
    Feb 24, 2021 at 19:10
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While coal is a rich source of chemical energy, without an oxidizer of some sort you are really only sitting on top of a pile of potential rather than a real source of energy. Most of the oxygen on Mars is chemically bound to the rocks (hence the red colour of Mars), and separating the oxygen from the rocks will consume a great deal of energy, far more overall than you will probably gain from burning coal in the newly liberated Martian atmosphere.

Assuming there is some reason that the Martians can't simply build or import more nuclear reactors or plant more solar panels, the Martians may be able to resort to some sort of electrochemical trickery to squeeze as much energy as possible out of the coal from their existing oxygen supplies. In essence, what the Martians need to do is create a fuel cell that can work with finely powdered coal dust rathe than simply feeding coal into a furnace and burning it. Fuel cells avoid the Carnot limit of energy conversion (for coal and most types of combustion this is typically @ 30% without some really heavy duty engineering add-ons to the process). Even reaching 50% conversion of the chemical energy of the coal into electrical energy would be a huge improvement, and this also has add on effects for the Martians, including eliminating the need for capital intensive boilers, turbines and cooling systems, and making the power plant itself more compact. This document suggests that conversion to electrical energy could be as high as 80%:https://str.llnl.gov/str/June01/Cooper.html

So the short answer is this is pretty impractical for people on Mars, while the longer answer is “yes, under some pretty tight constraints”.

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It's hard to imagine how we could get a coal cargo ship to Mars, and bring it back, fully laden, without expending more energy than we would get from the coal. Let's say that the ship, empty, weighs 500 tonnes and brings back 1000 tonnes of coal.

According to a discussion here on the NASA Space Flight forum getting a 525 tonne ship to Mars requires $170M.

If we assume that the costs per tonne are the same to get back (might be less due to Mars' weaker gravity), and that on the return trip the ship weighs 3x as much as on the way out, then the fuel cost getting back is \$170M * 3 = \$510M.

That puts the total fuel cost at 680 million dollars, to get 1000 tonnes of coal, whose market price at the moment is \$48.60 per ton (according to Quandl), and so our cargo would net us nearly \$50,000 on the open market. That's a really bad return of investment.

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  • $\begingroup$ or could we use the fuel to power a Martians cities? the efficiency of solar panel would improve by that time but maybe burning coal could provide more energy by mass I don't know. $\endgroup$
    – user6760
    Aug 26, 2015 at 8:44
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    $\begingroup$ The issue with burning coal in Mars is that burning consumes both the coal and oxygen. Being the snobs they are, I assume Mars colonizers will want to use the little oxygen they have for some fancy thing like breathing and the like. $\endgroup$
    – SJuan76
    Aug 26, 2015 at 8:48
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    $\begingroup$ Breathing is overrated. $\endgroup$
    – Hackworth
    Aug 26, 2015 at 8:50
  • $\begingroup$ Good point about the oxygen @SJuan76. There's not enough of it to burn coal in Mars's atmosphere, and as you say people living in habs wouldn't want to burn up their oxygen supply, while simultaneously filling the hab with deadly carbon monoxide and lots of other toxic gases and particles. Coal, unlike charcoal, is a very complex substance full of lots of different hydrocarbons, some of which are very bad for you when realeased by burning: that's why you can't, or at least shouldn't, use coal on a barbecue for example. User6760, you've picked the worst possible fuel idea for Mars. $\endgroup$
    – Max Williams
    Aug 26, 2015 at 8:59
  • $\begingroup$ and how about this method? $\endgroup$
    – user6760
    Aug 26, 2015 at 9:19
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As luck would have it, one of the major obstacles to the terraforming of Mars is the deeply toxic nature of its soil (or rather, regolith) caused by an abundance of perchlorates.

From the paper, Perchlorate on Mars: a chemical hazard and a resource for humans

Perchlorate (ClO4−) is widespread in Martian soils at concentrations between 0.5 and 1%. At such concentrations, perchlorate could be an important source of oxygen

Extraction and refinement of oxidising salts by stripmining the regolith might, in fact, provide a means to burn coal. This will of course consume energy, but a fleet of solar driven stripminers could harvest oxygen at the same time as extracting other useful minerals from the soil, so the incremental energy cost needn't be punishing.

will people use them as their main source of fuel or there are better alternatives?

It rather depends on the existence of nuclear power... fission or fusion. The former almost certainly requires shipments of nuclear fuel rods from earth, as mining, refining and enriching uranium on Mars itself seems like it would be an enormously expensive enterprise, and probably take quite a long time to get going as well.

Almost any settlement on Mars is going to require some generating capacity to weather dust storms that could prevent the use of solar. Unless fusion has already become practical by the time your settlement is formed, it will almost certainly have a nuclear reactor (though possibly quite a small one).

A coal-fired plant might suffice, given suitable stockpiles of coal and oxygen, but in order to get such stockpiles in the first place requires the sort of infrastructure that almost certainly implies a nuclear powerplant is available. In that case, why would anyone bother burning coal?

No, what seems more likely is that the coal will first be used for scientific purposes, learning about the Martian carboniferous era and the things that lived during it. After that, it could be processed into more complex hydrocarbons eg via coal liquefaction or a coal-to-olefins process (for which I don't have a good link at present).

These hydrocarbons can then be used to create other useful chemicals such as polymers or pharmaceuticals, or perhaps fuels which can then be more efficiently and conveniently and cleanly burnt than coal (such as methanol or ethanol in a fuel cell) or maybe even rocket fuel if that seemed useful still, which rather depends on your tech levels.

Coal-fired heating and power on Mars seems like a last-ditch act of desperation, rather than sensible use of local resources.

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