aSOC: Plant physiology (on Mars?)


Hubble Space Telescope image of Mars

Several months ago Andy Weir’s The Martian showed up on the feed of personalised advertisements for Kindle books on my account. No surprise, I read tons of sci-fi. Preferably no magic or dragons, as I can only tolerate so much “any sufficiently advanced technology is indistinguishable from magic.” So-called “hard” sci-fi tends to be the what I like most, and I gravitate to authors that have a propensity for characters on “the spectrum” or that are artificial intelligences (::ahem::). In any case, I read the sample from Amazon for the ebook, and I didn’t get into it.

Then last Wednesday Randall Munroe mentioned it was a cool story on xkcd. So I read it, and it was awesome. It’s a story about a guy fixing things in space. The flippant personality of the protoganist (Mark Watney, aka Matt Damon) is actually a tried-and-true literary device used to explain technical concepts to readers without being patronising. There’s a specific name for it that my exocortex is failing to bring me right now, but in any case, Andy Weir goes a long way to make sure his story is technically legit.

But this is aSOC, and I have to mention at least one thing I think was a mistake. And that thing is: space potatoes. Watney’s official job description entailed two roles on the mission to Mars: botanist and mechanical engineer. These are bascially the two skill sets most likely to enable someone to survive after being abandoned on another planet, which is a convenient coincidence for our buddy Mr. Damon. He grows potatoes and (oh sorry, spoiler alert starting a few sentences ago) at one point he worries about “suffocating” the potatoes by leaving the space house for a few days, thus not providing the plants with the CO2 they need to “breathe.” One problem: plants don’t breath CO2.

Don’t get me wrong, plants definitely need CO2 to make triose phosphates, sugars, starches and cellulose, etc., but this isn’t what they “breathe” on a cellular level. Plants need to respire just like we do to power aerobic metabolism. Plants need CO2 for photosynthesis, not respiration. A metabolically active plant doesn’t photosynthesize at night, but in general it will still need a low level of oxygen to survive. And I sure would have liked to see an energy balance for his indoor Mars farm. Photosynthetically active radiation on old Terra is about 300 Watts per square meter, and I’d be surprised if the reading lights in his space house are up to the task of meeting that level of output.

In any case, I can recommend that you go ahead and read the book, maybe watch the movie later, and think about space some more.