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Having recently seen Robinson Crusoe on Mars, I of course noticed how unrealistic it is. However given that it was released in 1964, before the first landing of any space probe on Mars, I wonder how realistic it was based on the state of knowledge about Mars back then.

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    "I wonder how realistic it was based on the state of knowledge about Mars back then." 'Not very'. I recall one of the Sci-Fi greats (Asimov?) commenting on (OK.. apologizing for) a story he'd written with WTE *"Yeah.. we already knew the chances of life on Mars were slim when I wrote that story (in the 50s) - but I chose to ignore that for the sake of the narrative". Commented Oct 17, 2015 at 10:47
  • @AndrewThompson: On the other hand, IIRC the only life forms he encounters on Mars are (1) visitors from another planet, and (2) some plants (which might not be originally from Mars, but also be brought there by those other visitors).
    – celtschk
    Commented Oct 17, 2015 at 13:20

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Although a great film from a stylistic viewpoint, Robinson Crusoe on Mars was unrealistic in many ways even by 1964 scientific standards. Even though it was released a few months before the Mariner 4 flyby in November 1964 when it took the first closeup photos of Mars, scientists already knew quite a bit about Mars even before then.

The biggest issue was the atmosphere. It is now known that the Martian atmosphere is roughly equivalent to Earth’s atmosphere at about 90,000 feet. But while that was not known to that level of precision in 1964, it was already understood that the atmosphere on Mars was very thin. In 1929 a French astronomer measured sunlight scattering on Mars and calculated that the pressure on Mars was no greater than the equivalent of 75,000 feet on Earth.

The problem is that atmospheric pressure this low without a pressure suit would be fatal. Just using an oxygen mask is not sufficient. The Armstrong Limit (named after the person who defined it, not Neil) sets this limit at about 60,000 feet on Earth. Above this altitude a person’s blood would literally boil and they would be dead in less than two minutes. That's why pilots who fly in high-altitude planes like the SR-71 wear pressure suits.

Crusoe spacesuit

The next issue is the oxygen level in the Martian atmosphere. It was also known by 1964 that there was only a trace amount of oxygen on Mars. In fact in 1934 an astronomer used spectral readings to determine that the oxygen level on Mars was less than 1% of Earth’s. In Robinson Crusoe on Mars Draper is able to breathe supplemental oxygen that he obtains by heating some rocks inside his cave. Somehow this rejuvenates him enough that he is able to get along just fine for periods of time in the Martian atmosphere without supplemental oxygen. And for longer duration explorations he brings oxygen with him in a canister, sort of like bringing a canteen of water for occasional sips. However the human body does not store oxygen the same way that it stores water and carbohydrates. You can’t just take a puff from an oxygen mask like an NFL lineman on the sidelines and then be good to go again in the 1% oxygen atmosphere. Survival at that low level of oxygen would be measured in minutes even if we disregard the problem with the low pressure.

Oxygen canisters

Now the oxygen pills that Friday turned Draper on to might actually work, at least in theory. The average person breathes about 6 liters of air per minute. About 1.25 liters of that is oxygen. But actually we only consume about one-fourth of the oxygen that we breathe in, so we consume about 0.3 liters of oxygen per minute. Oxygen weighs 1.42 grams per liter, so we consume about 0.4 grams of oxygen per minute. A typical vitamin pill weighs 1.5 grams. So if each of Friday’s oxygen pills weighed a similar amount then each oxygen pill would be good for about three and a half minutes, so Draper would need to pop about seventeen pills per hour. That number of pills would be doable, even if a bit of a hassle. Just make sure to not take a nap when outside the cave.

But we run into some other problems with the oxygen pills. It has only recently been discovered that mammals absorb some amount of oxygen through their intestines. So presumably humans do also. After all we have air in our digestive system which gets there by swallowing. But it is not known what percentage of the oxygen in the digestive system gets absorbed into the bloodstream. It’s doubtful that the intestines are as efficient as the lungs, but let’s go with that for now, so let’s say about one-fourth of the oxygen in the pills gets used. That means Draper has to take about one oxygen pill every minute, or sixty per hour. And it's not clear how fast it would be absorbed, or if you could take a handful of pills and be good for a while. It would take some experimenting, but one mistake and the experiment is permanently over.

Also you can’t just have a pill made up of 100% oxygen, because pure oxygen will only exist as a gas or as a cryogenically chilled liquid. So we have to assume that Friday’s pills contained some type of chemical that had oxygen as part of the makeup. Nitrous oxide as an example (N2O) is 36% oxygen by weight. But let’s say that the superbrain chemists on Friday’s planet came up with a pill that is 50% oxygen by weight. But that still doubles the number of oxygen pills needed. So basically Draper is going to have to be constantly popping oxygen pills into his mouth like peanuts.

A couple of items aren’t too problematic. One of them is temperature. In the 1920’s scientists estimated surface temperatures on Mars to be around −121 to 45° F. However once probes started going to Mars they found that while nighttime temperatures, or even just being in the shade can be frigid, in direct sunlight it can be quit comfortable depending on the season. As long as Draper stayed out in the sun or in his heated cave he should have been alright. But in some of the situations that he was in it wouldn’t have worked to just hang out in a T-shirt like he seemed to do all of the time. I guess he was just one tough dude.

Another one is gravity. Mars has 2/5th the gravity of Earth. So you would definitely feel lighter. And it would look a bit different when someone walked around in low gravity. But that is very difficult to simulate in a movie, so it’s understandable to not even try, which is the case with most sci-fi movies. If you want to see an example of how people look in simulated Mars gravity, Fran Blanche has a clip from her zero-g plane flight. Those flights usually do a combination of zero-g, Martian gravity and lunar gravity, in fact she has a clip of lunar gravity also in her video What Does Real Martian Gravity Look Like?

But we shouldn’t totally dump on the science of Robinson Crusoe on Mars, because they got one thing very right and that is the surface geology. Prior to the Viking Lander missions in 1976 no one knew what the surface of Mars was like. In fact the best Hubble Space Telescope image of Mars only has a resolution of 5 miles per pixel. Even Mariner 4 which flew close to Mars in 1964 only had a resolution of 2 miles. Scientists thought Mars would probably be similar to deserts on Earth, and it seems that the Robinson Crusoe on Mars art designer went with that. Since the Viking landings many Mars probes and rovers have visited the planet, including the recent photo on the right below which was taken by the Perseverance rover in 2021. It doesn’t look that much different than the photo on the left of Draper and Mona walking on Mars.

Mars comparison

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