I just finished reading The Martian by Andy Weir a few days ago. I’d previously watched the film a few times, but hadn’t picked up the book yet. I rewatched the film this weekend to refresh my memory, and now I’m happy to compare the two.

This brief article is going to contain spoilers for both, so if you haven’t seen/read them and you care about not knowing what happens, you can leave now. I’m guessing that more people will have seen the film than read the book, so I’m going to attach a rudimentary spoiler tag to book-specific things. You can hover over those on desktop or click them on mobile. If you use a screen reader, it’ll say “(Warning: Spoiler Text Follows)” before the spoilered text.

You have been warned.

The first thing that struck me about the book was how good of an adaptation the film was. The characters in the book felt just like the characters in the movie. It really felt like I might just be reading the transcripts of some of the video logs from the film.

The next thing I noticed was that the book felt a lot more science-y (or perhaps calculation heavy) than the film. In the book, Watney obsesses over calculations for the first few chapters to try to figure out how to grow enough food to last until the Ares 4 mission arrives in ~900 Martian Sols. He estimates the relative caloric output of session of potato farming, and uses that to calculate how many square meters of land he needs. He even stresses about how he doesn’t have enough space and has to come up with other solutions, which I enjoyed. From there, he calculate how many litres of water he needs to feed the plants. In the movie, this is just waved away as ‘Watney needs to make water’.

Another example of this is when Watney is trying to figure out how many solar panels he needs to take on his journey. There’s a lot of numbers given about the capacity of the battery (18000Wh), the number of hours of daylight at that time of year for that location on mars (13 hours), the power received by the surface from the sun (500 to 700Wm-2) and the efficiency of his solar cells (10.2%). From this, he calculates that he needs 28m2 of solar panel. The thing is, before I had even read the sentence where he had calculated that (literally the next line on the page), the inquisitive engineering part of my brain plugged all of those numbers together and worked it out too. So it was incredibly rewarding to be able to read his answer and know how he got there. This kind of pattern repeated throughout the book.

The solutions to the challenges that Watney faces are more nuanced in the book, too. From simple things like figuring out how to store the water that Watney is making, from having to find a safe way to burn excess hydrogen that he’s producing. The film doesn’t cover the former, and plays the later for laughs. This makes sense because it takes many hours to read a book, but you only get 2 hours to watch a film. So logically you can fit more details in to a book.

But there are also more challenges in general. The book and film run in parallel for roughly the first half, but then the book throws a curveball by having Watney (Warning: Spoiler Text Follows)accidentally break his radio with his drill. That was far more interesting to me, because once Watney had established communication with NASA, the book came to be more of a “oh I’m doing this because NASA told me to” rather than “I’m figuring this out aloud and you get to enjoy the problem solving.”

Another example would be that during his trip to the Schiaparelli Crater, (Warning: Spoiler Text Follows)a storm appears that has the potential to kill him by blocking his light, and naturally he has to detect the storm and figure out how to solve it on his own.

There are a few moments in the film that don’t make sense on their own. For example, at one point Watney says “I’m about the leave for the Schiaparelli Crater, where I’m gonna commandeer the Ares 4 lander. Nobody explicity gave me permission to do this, and they can’t until I’m on board Ares 4. So that means I’m going to be taking a craft over in international waters without permission. Which, by definition, makes me a pirate.” Ignoring whether Watney is correct or not, one thing sticks out to me? Why couldn’t NASA give him permission? That’s the question I asked in the cinema. In the book, this is explained implicitly by the fact they can’t contact him (Warning: Spoiler Text Follows)after he broke the radio.

But this can’t be the case in the film, because we see him staying in contact with NASA right up until he arrives at the Ares 4.

There’s also a moment in the film that just makes no sense and where science has clearly been thrown out of the window. Watney and NASA have just established proper text communication with each other for the first time. He asks them how the crew from his mission are doing, and what they said when they found out that he was alive. At this point in the film, NASA haven’t told the crew, so Kapoor and the rest sit around looking sad and not knowing what to type for a few beats as they debate what to say. Apparently this takes long enough for Mark to be concerned that they didn’t get his message, so he asks “RU Receiving? Mark”.

The average round-trip travel time for the speed of light to go between Earth and Mars is 28 minutes. So it took 14 minutes for Watney’s message to get to earth. Watney then presumably waited at least another 14 minutes to become concerned about whether they received his message. For Watney’s second message to reach Earth, a full round-trip would logically have had to occur (assuming Watney is sensible and waited for an appropriate period to send his message) Kapoor is seen with Watney’s “RU Recieving message” on the screen as he starts typing, so we can assume that a full round trip time has elapsed for Watney’s message to have reach them. Are we meant to believe that Kapoor and everyone at the screen waited for 30 minutes without gathered around the screen without moving or typing anything? Even when Mars and Earth are at their closest, there’s still a 3 minute round trip time. The film portrays it as moments. Just my small gripe.

So far, it may seem like I’m just bashing on the film, but I’m not. I think the film is great, one of my favourites, and I’d recommend that anyone watch it. I think it’s funnier than the book - in some parts anyway - partly because you have the whole realm of visual gags, audio gags, and joke timing that you just can’t get with the written word.

P.S. I'm late to the party, but I recently got a twitter account that you can follow here.