The novel
The Martian
It was a thought experiment that led software engineer Weir to write his 2011 novel, also titledThe Martian. The book is written mostly from the point of view of American astronaut Mark Watney, who is accidentally left for dead on the Martian surface. He has limited supplies and resources and, initially, no way to contact Earth. In effect, Weir’s novel figures out how an astronaut could survive under these conditions and get himself rescued.
The book is a breezy, easy read. Although the author concedes a couple of scientific flaws in the foreword, on the whole, the book was surprisingly accurate and enjoyable. To some degree, its scientific accuracy shouldn’t surprise us. Weir’s father was a particle physicist and it’s also clear that Weir diligently researched the book’s details. As a novelist, he could, and did, choose not to depict in detail the futuristic equipment that the astronauts take to Mars.
When it was announced that 20th Century Fox had bought the movie rights and that Ridley Scott had signed on as director, expectations were high among the book’s avid fans that the movie retain the book’s scientific realism. I’m happy to report that this is indeed the case, with a few reservations. I’ll intersperse my limited criticism of the science with my assessment of what is done well.
The movie
Because the book starts on Mars, the book’s readers learn little about the voyage to Mars itself. The same is true of the movie. With current technology, the trip to Mars would take at least 150 days. There are a number of ways by which a spacecraft can be sent to the red planet. The most energy-efficient routes put the spacecraft in a highly elliptical orbit that takes the spacecraft far beyond Mars once it deposits the astronauts on the planet’s surface. This energy saving is offset by the fact that if something happens to the astronauts on the planet, there’s no option for a prompt return to Earth.
A colleague at Physics Today asked me whether the spaceship in the movie required aerobraking to get into orbit and therefore needed thermal shielding for the maneuver. The answer is probably not, but the astronauts’ landing craft might need shielding, depending on with what speed it departs the main craft (relative to the planet), and on how much fuel is needed for landing and returning. You can also always use parachutes to retard a descent, although they would have to be fairly large because of Mars’s thin atmosphere.
The Hermes spacecraft
Radiation is a serious problem for a Martian mission. Once astronauts leave Earth’s magnetic field, they risk receiving large doses of radiation from solar flares and cosmic rays. Much of the radiation can be stopped with a few sheets of plastic, but the more potent particles would require a lot more shielding. One solution is to build a protective cabin for the crew by using either metal or water to absorb most of the radiation. Deflecting charged particles with a compact and powerful superconducting magnet is another feasible solution.
The movie spacecraft is spacious, with lots of windows. Unless a new way of shielding the crew from radiation had been discovered, this design seems unfeasible. In fact, in an interviewin Science magazine, Weir admits that radiation shielding is one of the problems skipped over in the book and movie. “I just said that in the intervening time they'd invented some kind of material that takes care of it,” he admitted.
Radiation remains a problem for a Martian crew when it arrives on the surface of Mars. That’s because the planet’s magnetic field is too weak to serve as a shield against solar and cosmic radiation. For that reason, some designs for Martian habitats propose covering dwellings with dirt or tunneling into the side of a hill.
Another scientific criticism of the movie is the violence of the weather on Mars. Granted, the planet has massive sand storms, but the atmosphere is too thin and the pressure is too low to blow satellite dishes off their support structures and into the crew members. In addition, there’s a scene late in the movie in which a tarp blows in and out with the movement of the storm to indicate how fragile Watney’s habitat has become. That couldn’t happen on real life Mars. Again, Weir readily acknowledges this flaw in his book.
Artistic license in the movie—but not in the book—is that Mars looks too bright in the daytime. Mars is roughly 50% further away from the Sun than the Earth is, yet the Martian surface in the movie looks like a bright day on Earth. I suspect that the Sun would appear smaller on Mars than it does in the movie. Also, both Martian moons should move quickly across the sky, but instead they seemed sluggish—though that could be an artifact of the “3D” print I was watching. On a more positive note, the color of the sky is spot on.
The film visualizes Watney’s habitat remarkably well. Apart from the airlock, there’s not much detail about the interior in the book, so it’s clear that the filmmakers had consulted closely with NASA or other experts to make the habitat look realistic. Some of the equipment could have come from the International Space Station. For example, Watney breathes oxygen manufactured from Mars’s carbon dioxide atmosphere, and that’s also how astronautical engineers conceive it would be done.
Most of the geology is extremely accurate. One of Watney’s main problems is procuring enough food to survive, so he attempts to grow it on Martian soil. That’s an interesting challenge in its own right. We know that Martian soil is fine and resembles Martian atmospheric dust. The soil contains several metals and is rich in sulfur and chlorine compared to terrestrial soils (see "The Enigma of the Martian Soil," Science 309 888 2005). As both the book and movie presumes, Martian soil lacks organic matter and water, which Watney has to supply and add himself.
On the plus side for Martian gardeners, depending on location conditions and additional artificial sunlight, the planet’s soil is either slightly alkaline or fairly acidic, the latter of which is good for growing potatoes. But the soil is also highly reactive. Any organic matter that comes into contact with it could decompose unless the soil was treated first. A biologist could explain better than I the likelihood of growing food using the techniques described by Weir (and in fact,there's an experiment on to try exactly that). As for eating Martian crops, the heavy metal and sulfur content would eventually make you sick. Watney does indeed suffer a number of diet-related medical issues by the end of the movie, though (apart from starvation) the reason for these is not detailed.
Most of the time the filmmakers got gravity right. When Watney walks across the surface, it looks like he performs little hops, as you would do on a planet with gravity less than the Earth’s (0.38 Earth gravity). Low gravity also accounts for Watney’s ability to move heavy equipment. Some other parts of the movie didn’t convey the planet’s lower gravity as effectively. Liquids, like the ketchup Watney uses on his food or the water in his cultivation system, flow more quickly in the movie than they would in real life.
Watney is shown to be sweating a lot in his spacesuit, which seems realistic. He also gets cold easily, and this too seems right. Heat dissipates quickly on the Martian surface, with an outside temperature ranging from −67°C to 20°C around the equator.
The meetings at NASA and the Jet Propulsion Laboratory on how to save Watney hark back to the near disaster that befell Apollo 13 in 1970. They strike me as very realistic. One exception is a scene in which the NASA director and a scientist discuss orbital mechanics. Its presence in the movie presumably serves to provide an opportunity to tell a less-informed audience about the rescue mission’s trajectory.
The movie skips one of the major forays that Watney makes in the book. The omission is understandable, given that the movie, cannot include everything in the book despite its 141-minute running time. I was pleased to see that the filmmakers generally got the sand right. Martian dunes consist of large sand grains, which appeared true to life in the movie. I would not be surprised if some of the images were taken directly from surface footage of the planet.
The final dramatic act of the book has some neat orbital mechanics, partly artistic in nature, which I’m not going to divulge in this review. The movie successfully (though not entirely faithfully) reproduces that dramatic moment from the book.
In summary, although there are some minor scientific details that are glossed over, on the whole the film is pretty accurate. In terms of realism, The Martian is a worthy successor to2001. Surprisingly, unlike Stanley Kubrick's masterpiece, Ridley Scott's movie is a great one for families. There is minimal swearing, little violence, and a wry sense of humor. Matt Damon is great as Watney, and he successfully captures how lonely and isolated such a person would feel and how determined he would be to survive. The rest of the cast ably support the story, particularly Chiwetel Ejiofor as NASA engineer Vincent Kapoor and Jeff Daniels as NASA director Teddy Sanders. Of all the movies I've seen about the red planet, only Roving Mars, a 40-minute documentary released in 2006, delivers as much fun.
One final note: The version of the movie I saw was in 3D. For some scenes, the viewer’s experience might be better in standard high-definition film. Confirming that hunch will give me another excuse to watch this movie again.
Acknowledgements: All images courtesy of 20th Century Fox.
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