Saturday, September 26, 2020
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Movie review: The Martian

The Martian, a movie released on October 2, is well over 90 percent “fresh” on Rotten Tomatoes, which almost certainly means it’s a good movie. I won’t dispute that rating but will add that the film has value in math and science classrooms as well as in film studies.


The Martian makes science fiction as realistically scientific as possible. (20th Century Fox Film Corp)

Matt Damon plays Mark Watney, a NASA astronaut who has to survive on Mars after being accidentally left behind by his crew. Stranded on Mars, he has to quickly acquire the skills of a botanist and other scientists in order to grow food on the Red Planet, where nothing is alive. As such, he endeavors to “science the s**t out of” everything he can get his hands on.

The movie is directed by Ridley Scott, who fantastically mixes space shots of Mars with careful close-ups of actors’ faces. It’s based on a novel by Andy Weir, who reportedly did a lot of research to make the scientific and technical aspects of the story as realistic as possible. (Parental warning: One of Watney’s first log entries is this: “I’m pretty much f***ed. That’s my considered opinion. F***ed.” The publisher considered releasing a “school version” of the book and may do that at some point in the future.)

I hate to break it to you—because the humanistic elements of the story, including a daring rescue plot masterminded by Watney’s crew and a scrappy ingenuity and instinct to survive on a strange world, are highly creative—but the science is very close to impossible.

Without liquid water, which may have existed at one point but probably doesn’t exist on the Martian surface anymore, Mars isn’t capable of sustaining human life for long. There certainly wouldn’t be enough time to get a rescue mission up there.

Watney creates water by burning hydrazine, which I think could work, but you would need a whole lot of it. This is a simple chemistry problem in molar arithmetic, and the Entangled Continua blog discusses it, with some useful user comments, at great length.

That doesn’t mean the film has no educational value for scientists or science students. Watney’s acknowledgment that it’s dangerous to burn hydrazine in an open space with all those other chemicals around to make water, which probably won’t be enough anyway, presents the audience with a useful safety analysis, tied into the plot of the film.

Plus, when he takes a dozen or so Thanksgiving potatoes and turns them into a crop of potato plants in the Martian soil and fertilizes them with his own waste, he definitely takes a page out of agriculture. He’s just going to come up short on water, I think.

But ignoring the likely scientific impossibilities, there are great math opportunities in the film; you just have to use your imagination. Once you get past all the swearing, math problems come into focus, including this one from Chapter 3, Sol 25:

Remember those old math questions you had in algebra class? Where water is entering a container at a certain rate and leaving at a different rate and you need to figure out when it’ll be empty? Well, that concept is critical to the “Mark Watney doesn’t die” project I’m working on.

I need to create calories. And I need enough to last the 1387 sols until Ares 4 arrives. If I don’t get rescued by Ares 4, I’m dead anyway. A sol is 39 minutes longer than a day, so it works out to be 1425 days. That’s my target: 1425 days of food. …

I need 1500 calories every day. I have 400 days of food to start off with. So how many calories do I need to generate per day along the entire time period to stay alive for around 1425 days?

The book spares the reader the math, but teachers can certainly take Watney’s computed answer of (about) 1100 calories per day and check his work in their algebra classes. Don’t forget the fact that he was writing that on Sol 25 and hadn’t planted anything yet. If x represents the number of calories he needs to generate per day, here are some incomplete calculations:

(1500)(400) + 1425 x - (1500)(1425) \ge 0
1425 x \ge 1,537,500

How can you modify this model to account for the fact that potatoes will take a while after being planted to become edible?

In conclusion, math is a go in The Martian, and the film at least opens up some useful discussions in science classes. And see the movie in addition to reading the book for Mr Scott’s cinematography and Mr Damon’s impeccable sense of timing, even when he’s the only human for millions of miles. But make your vision a little blurry when it comes to the effects of weightlessness in space travel. The mistakes are of little consequence to the underlying math and biology, regardless of what physicists might tell us.

Paul Katula is the executive editor of the Voxitatis Research Foundation, which publishes this blog. For more information, see the About page.

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