A Nitpicker's Review of the Movie The Martian

I watched the movie last weekend, and I have to say that, overall, I was impressed by its technical correctness.

That said, I have to pick a few nits.

Martian Surface Gravity is Not One Gee
(For obvious reasons, such as expense) the movie depicts Mars' surface gravity at one gee (one Earth-normal gravity). In fact, Mars pulls about one-third gee. Movements would be different, and things would fall more slowly than here on Earth.

Cumulus Clouds
In one of the opening shots of the movie, Mars' sky is depicted with a row of cumulus clouds down near the horizon. That's a no-no. Clouds on Mars are wispy cirrus and quite high up.

The Dust Storm
Okay, there's a couple of things wrong here. Point one: a Martian dust storm approaching from a distance would not produce thick rolls of dust, as we see cascading down the mountainside towards the camp. Point two: it would not blot out the sky and make everything dark, as Mars' atmosphere is too thin for that. Point three: although the wind speeds are high in a Martian dust storm, Mars' atmosphere is so thin that it would be like a gentle summer breeze on Earth, with no catastrophic damage to infrastructure and human beings.  Point four: Martian dust is silt-fine, yet the movie featured particles the size of snowflakes. You don't even get that on Earth.

"I'll Implode"
While the protagonist records a log entry, he states that if the habitat lost pressure, he would implode. Quite the opposite, actually; his body would try to explode from the steep drop in pressure.

Items Dangling and Flapping in the Wind
See The Dust Storm, above. In one of the penultimate scenes in the movie, he's shown hauling a tarpaulin over the nose cone of the escape rocket. Said tarpaulin is strongly lifted by the breeze, flapping away like on Earth.  No.

Consumables
It's not clear where he's getting all that extra oxygen for long trips into the Martian desert.

The Spare Pathfinder
The movie depicts this as activating along with the one actually on Mars. Sorry, but this just wouldn't happen in real life. That said, I experienced a whoop of joy when he dug it up (something that could conceivably happen in future).

Takes More than Plastic and Duct Tape
In one scene, after losing pressure in the airlock, he's seen sealing the blown-out habitat with sheet plastic and duct tape and then re-pressurizing. Any high-school kid can tell you that it'd take a lot more than that to hold in the twelve pounds of pressure it's inflated to. The actual total pressure there would be many tons (about twenty-four, from a quick back-of-the-envelope calculation, assuming the diameter of the entranceway to be about six feet).

That said, it was a fun and inspiring movie, and I can only hope it's inspired the next generation of aerospace engineers.
-Bill