There has been a lot of talk about the main character in the movie "The Martian" shoveling piles of Mars dirt into his greenhouse and successfully growing potatoes until he was rescued. Is this really possible on Mars? And what did the movie NOT tell you.
Firstly, let's clear up some misleading data from scientists using crushed volcanic rock from Hawaii as a "Martian Soil Simulant" to prove that we could grow plants on Mars. Of course they can grow plants and vegetables (and bacteria and earthworms) in Hawaiian volcanic rock dust -- it's from right here on Earth, in the Earth's atmosphere and environmental conditions. Sheesh. Sometimes I think these "scientists" are just going through the motions. They aren't even using data from NASA rovers and ESA. Data from 1970s and more recently in 2008 and 2012, completely ignored by these "experts."
The truth is that Martian "soil" has been shown to contain highly toxic oxidizing compounds called "perchlorates" -- chemical compounds that will interfere with Thyroid function in high enough concentrations. And, yes, NASA and ESA measurements say two things: 1) Perchlorates are found in high concentrations and 2) Perchlorates seem to be evenly distributed globally on Mars. Worse, even right here on Earth, is that perchlorates have a tendency to contaminate drinking water and gain entry into your body mainly through drinking contaminated water.
Is Mars Habitable?
Even though perchlorates are used here on Earth in fireworks, rocket fuel, explosives and a host of other things that one would never consider eating it is possible for an adult to survive short term exposure to perchlorates, especially if they can take an iodine supplement to counteract the adverse effects such as permanent thyroid malfunction. So Hollywood gets a pass on this one, it would appear, but only because the astronaut was a male and not a pregnant female or a child. Perhaps the movie ended before Matt Damon's thyroid would have shut down, or perhaps it's just movie magic: making an inconveniently toxic chemical disappear so the hero could survive (at least long enough for the box office returns to come in anyway).
Short term exposure might be ok, what about long term? Well, that would not be so good. Symptoms of perchlorate toxicity include eye irritation, skin rashes, coughing, nausea, vomiting, diarrhea, disruption of the thyroid function and hypertrophy of the thyroid gland, and weight loss. These are known problems caused by perchlorates right here on Earth by the way.
The good news is that perchlorates can be used to create rocket fuel and can be processed to produce oxygen. Calcium perchlorate is CaClO4 (calcium, clorine and 4 oxygen) and aluminum perchlorate is AlClO12 (aluminum, clorine and 12 oxygen). All that is needed is some clever techno-gadgetry to separate the oxygen. At between 0,5 and 1 percent concentration in the Martian regolith it might be that perchlorates are a resource more than a danger. And drinking water can be filtered using standard methods such as reverse-osmosis filtering, ion exhange membranes or even bacteria.
Soil contaminated with perchlorates can be thoroughly rinsed to reduce the levels to what is considered "safe" here on Earth. That would waste lots of water otherwise needed for humans to safely drink and bathe. But it is possible.
Now that we've covered the bad news, let's get on to the good news. From what I've read the soil on Mars does contain nearly all the necessary components for healthy plant growth. CO2 and Nitrogen are found in the Martian atmosphere (Nitrogen concentration is about 2,7 percent on Mars). Nitrogen is also found in Martian soil at a lower concentration of 0,1 percent. Future Mars inhabitants will probably need to find a source for zinc, molybdenum and copper, but only in very small quantities of perhaps 1 kilogram per person per year combined. But that's only a back of the napkin guesstimate. And it is possible that these elements exist on Mars but we have yet to find them. Copper is mined here on Earth after all, not just lying around mixed in with the dirt.
Who can say what the first humans will find once they start living on Mars.
Edited for: actor's name in the movie.