Fact-checking The Martian

So, I got The Martian (the book) from the library and am gobbling it up.  I did have some initial resentment because there were few vivid sensory descriptions, no evocative emotions, and little character development in the first few chapters.  I just got a very nice rejection the other day because my novel doesn't have those things in the 50 pages the agent read.  And I was like--but you see, my character is very cold and cerebral, she isn't going to be pouring out evocative descriptions and feelings!  You should be picking up on her personality by the lack of those things!

And Andy Weir, in this book, does exactly the same thing and gets away with it.  Grr.  I'll tell myself it's because my book, too, can get away with it and I just haven't sent it to the right person yet.

Anyway, it does okay for itself, science-wise.  Lots of stuff about Mars and the methods used by the astronauts to set up their visit.  All very plausible.  But there were just a few times that I found myself shouting at the book because it got something wrong, and not just a bit inaccurate, but a huge problem that our main character should notice.

Mark Watney, the main character who is marooned on Mars, is a botanist and an engineer.  I know basically nothing about engineering, but it turns out I know kind of a lot about botany, and specifically about artificial closed ecosystems.  Mainly because they've played a pivotal role in my latest two novels.  It just maddened me that Mark is in a perfect situation to close the loops on the carbon, nitrogen, and water cycles, and he mostly does not do that.  When he does try to do it, to some small degree, he doesn't do a very good job or account for the most basic things.

Realizing he doesn't have enough food to last till he's rescued, Mark decides to start growing his own.  This is a great idea.  He only has three sproutable items in his food supply: potatoes, peas, and beans.  He decides potatoes are the best choice because he can get more calories per square foot of garden that way.  He's not worried about any other nutrients, you see, because he has a big ol' bottle of vitamins.

That's where I started getting annoyed.  Calories and vitamins aren't the only things you need to live.  You also need protein.  Most of us don't worry too much because there is plenty of protein in any normal diet.  But if you don't get protein, you'll get protein deficiency or kwashiorkor, which causes muscle wasting and poor healing.  You really have to get some.

One potato is 163 calories and gives you about four grams of protein.  If we assume he eats about nine per day, he'll only get 40g of protein, and he should be getting 56g at a bare minimum.  Does he ever worry about this?  Does mission control?  Does he have trouble carting around heavy weights in a spacesuit?  Nope, never!

If you're ever in this scenario, plant the beans.  Probably the smartest thing is to diversify the indoor garden and do some of each thing.  I'll forgive him for not doing peas, though--odds are good they're split.  Split peas won't sprout.  An extra advantage of both peas and beans is that you can, if you have to, eat the leaves also.  Potato leaves are toxic, so there's all this plant matter that has to be simply thrown away.

The last annoyance here is that Mark freeze-dries his potatoes because if left inside "they will rot."  Has Mark ever owned a kitchen?  As long as it's cool and dry, the potatoes will be fine.

So much for the choice of potatoes.  What about the rest of the farming project?

Well, plants need a few basic things: carbon dioxide, light, water, various minerals (especially potassium and phosophorus), and nitrogen.  Mark, being a botanist, just says they need carbon dioxide, water, soil, and soil bacteria.  There's a great deal of fuss over him having this tiny little bit of bacteria and inoculating the soil and mixing in his own feces for it to decompose, because as we all know (because he told us) plants can't grow without soil bacteria.

And . . . that's simply not right.  They need nitrogen.  Normally at least some nitrogen is provided by soil bacteria (especially if you planted peas or beans) but most gardeners end up introducing their own because the soil on its own isn't as productive and will wear out.  (Mark points out that gardening as heavily as he is will exhaust the soil, but doesn't really explain why, or that this can be prevented with proper inputs.)  All this fuss about bacteria and he doesn't really need it!  He has two other available sources of nitrogen, maybe three.

1.  In order to farm, Mark needs water.  He has plenty of oxygen, but he needs hydrogen to make the water.  He decides to make it by breaking down rocket fuel, hydrazine.  A molecule of hydrazine has two nitrogen atoms and four hydrogen atoms.  It's horribly explosive, which is the focus of this episode, but at the end Mark has hydrogen, plus most of the nitrogen was released as harmless gas.  But he adds, "Chemistry, being the sloppy bitch it is, ensures there'll be some ammonia that doesn't react with the hydrazine, so it'll just stay ammonia.  You like the smell of ammonia?  Well, it'll be prevalent in my increasingly hellish existence."

Mark, being a botanist, somehow hears "ammonia" and thinks "stink."  I am only a home gardener, but when I hear "ammonia" I think "usable nitrogen."  Of course it's only a tiny bit and Mark doesn't even need it because he has soil bacteria, but when later the soil bacteria die, he could very well produce any amount of ammonia out of the hydrazine.

2.  Of course that's really an excessive amount of work given that every single human has a virtually endless supply of ammonia.  Namely urine.  Mark's is handled by the water reclaimer (we are never told what it does with the stuff it filters out) but if he saves his poop to garden with, he absolutely should be saving his urine too.

In its raw form, urine isn't good for much, but given a little time and some urease enzyme, it'll break down into ammonia.  Much of this will evaporate and be lost (that evaporation is why pee stinks) but some will be useable to put on the garden.  Urease enzyme is basically everywhere, including on your skin.  Mark clearly has some in his environment, because when he has to pee in a bucket, it smells "like a truck stop men's room."  Fresh urine doesn't smell bad unless you're ill. That smell comes from ammonia. How does the nitrogen get into your urine? From digesting the protein in your food. It's a neat little cycle!

So, all he's gotta do is age his urine for a few days and carefully apply to the soil.  As a botanist, he'd probably have a good handle of how much to put on; you wouldn't want to overdo it (i.e. don't go out right now and water the garden with your pee, it'll probably get nitrogen burn and die).  No nitrogen-fixing bacteria required!  Again, he initially had the bacteria so I can see why he didn't worry about this method, but later it seems like it would start sounding like a better choice?

3.  The third option is trying to rig something to get the nitrogen out of the air.  That's how artificial fertilizer is made today, but I admit I don't know exactly how it works or whether it would have been possible for Mark.

The next concern I would have for the plants was lighting.  We're never told if the Hab is translucent, but we are told it has plenty of electricity from the solar panels and several chapters into the gardening thing, he mentions in passing that there's plenty of light.  Which is actually surprising--I mean, who bothers to put broad-spectrum, ultrabright grow lights if you just want the astronauts not to be in the dark?  I thought I'd be up for him removing all the lights from other parts of the Hab and rigging up something to get them as close as possible to the plants, but noooope.  Not even mentioned.  His yields suggest the light was adequate though.

Next quibble is with the water cycle: Mark has gotten himself some water, which he pours on the soil as needed.  The water evaporates and makes the air humid, but that's no problem because the water reclaimer condenses any extra humidity.  There's a minor snag because there's a clog in the reclaimer from "soil minerals."  But the soil never goes into the water reclaimer.  The water evaporates, meaning it leaves all minerals behind.  It's distilled.  WHAT A MYSTERY.

That makes the sum of the farming quibbles.  I had one about how Mark thought he could save energy by going without heat (um, food energy is still energy and cold will increase your metabolic rate!) but as he discarded that plan when he found out how cold it was, I'm gonna let it go.

Next, a small chemistry quibble.  When Mark makes the water, he describes the chemical formulas in terms of liters: "50 liters of O2 makes 100 liters of molecules that only have one O each"; "Each molecule of hydrazine has four hydrogen atoms in it.  So each liter of hydrazine has enough hydrogen for two liters of water."  But . . . that's not how it works.  Volumes aren't used for much in chemistry because different substances vary in density.  You'd need to be measuring in grams, or better yet, moles.

The last and most obvious problem is how Mark recharges the rover with solar panels.  He has to spread them out to soak up sun, so he can't drive while charging.  He starts at dawn, drives until the batteries run out--four hours--and then spreads out the solar panels.  It takes them twelve hours to charge.

How long is the day on Mars?  Isn't Mark going to run out of daylight?

Mars's day is under an hour longer than ours, so on average it gets twelve and a half hours of daylight.  Let's say it's summer.  Mars's axial tilt is a bit more than ours, but not by a lot.  The latitude of Mark's camp is 31 degrees north, about the latitude of Houston.  Houston gets fourteen hours of daylight on the summer solstice.  Even if we give Mark another half hour for the Martian day length, and another half hour for the planet being slightly more tilted, I just don't think he's going to have time to charge up those panels before the sun goes down.  And I'm not sure they'll charge as fast those last few hours, with the sun getting low!

And then Mark takes another rover trip months later. So if the day was over 12.5 hours on the first trip, it's not now.  There's even a day where he drives eight hours, charges his panels, and runs out of daylight when they're only 70% charged. How do they get 70% charged in only 4-6 hours if it takes 12 to charge them fully?

It's especially annoying given that Mark could have just gotten up earlier and driven at night.  Why waste precious sun when your panels aren't up?  (Does the rover have headlights, I wonder?)  Did the author simply not remember that solar panels need sunlight? He gets that dust storms affect them, but seems to assume a day that's any length he wants for the plot.

That's all the errors I caught. If there are engineering problems, I wouldn't catch them.

So did it ruin the book for me? Actually no. I enjoyed nitpicking it. I guess it's the same impulse that makes people love Star Trek while publishing whole books of the errors in it.

I even grew to like Mark Watney. He's not a wildly emotional guy, he's a wisecracker. Which ends up helping him not go off his nut when he's alone on Mars.

So I'd definitely recommend the book. But Andy Weir, if you're planning another book involving farming in space? Call me first.