Our neighbouring planet Mars has always exerted a powerful pull on the human imagination. Its reddish brightness in the night sky, combined with its relative proximity and the idea that it might be a near-twin to Earth, has singled it out as a potential destination for Earth colonists. But such endeavours are not without risk. This article takes a look at three stories, each of which imagines a single Earth astronaut stranded alone on the Martian surface, and considers what they tell us about changing conceptions of Martian habitability.

For those who want a more visual experience, this blog is broadly based on a talk I prepared for National Astronomy Week 2020 and a recorded video version (18 minutes) can be found here.

 In the late 19th and early 20th Century it was still possible for writers to imagine an Earth-like environment on Mars. While astronomers were already establishing that the planet was arid, cold and likely geologically older than Earth, sufficient ambiguity remained to allow for planetary romances such as the Barsoom books of Edgar Rice Burroughs (1912-1946, starting with A Princess of Mars). In these stories an Earthman arrives on Mars through a form of astral projection, but finds a thriving ecosystem, more than one native sentient species, and no problem breathing or surviving in the Martian environment. These are fantasies rather than true science fiction, but they paved the way for more serious consideration of Mars-survival as our understanding developed.

One of the earliest stories to seriously consider the understood conditions on Mars and the life that might result from it was Stanley Weinbaum’s “A Martian Odyssey” (novella, 1934). In this story a chemist, Dick Jarvis, becomes separated from the first human expedition to Mars when his survey vehicle crashes. Salvaging what he can from the ship, he is forced to trek across 800 miles of Martian landscape, encountering a variety of interesting life forms. These range from an intelligent bird-like creature with a knowledge of astronomy to a silicon-based organism which excretes material in the form of small pyramids.

Jumping forward to 1964, we encounter the fantastic feature film Robinson Crusoe on Mars (based on Defoe’s 1719 novel [1]). In this story, astronaut Commander Kit Draper (played by Paul Mantee) crash lands on the Martian surface. His colleague, in another landing craft, is killed, and he is left to try and survive by making the most of his resources. For company, he has a trained chimpanzee he has brought with him from Earth and later he is joined by an alien companion who has escaped from enslavement by other, hostile (and, it should be noted, non-Martian) aliens. Ultimately these hostiles attack the planet in their hunt for the fugitive, forcing a daring escape plan.

Notably, this film’s advertising (as shown on the image to the right) makes the striking claim that “This film is scientifically authentic.. is only one step ahead of present reality!”, and - as we will see - until the arrival of the alien flying saucers, this does not seem an unrealistic claim.

More recently still, the 2015 blockbuster motion picture The Martian was based on a 2013 novel of the same name by Andy Weir. In this story, botanist Mark Watney (played by Matt Damon) is accidentally left behind when extreme weather forces the evacuation of a crewed mission to Mars. While his colleagues believe him dead, he too is forced to utilise what resources he has available in order to survive an extended period alone on the Martian surface. Eventually, his crew-mates learn of his ordeal and turn back to attempt to rescue him through a risky orbital manoeuvre. While the film detailed many of his efforts, the original novel goes into far more technical detail, and explores issues the film didn’t get a chance to focus on, providing a thoroughly-researched contemporary view of survival on Mars.

These sources span 80 years of evolution in both storytelling and our understanding of Mars [1a]. So why am I lumping them together? Well, the common theme element (of a stranded astronaut) poses some fairly fundamental questions about the concept of habitability - what does it take to survive on another planet, and how has our understanding of those needs changed over time?

Air to Breathe

Perhaps the most fundamental need of any human being is for air to breathe, and securing a supply of oxygen, as well as management of carbon dioxide build up, would be an urgent priority.

Here, “A Martian Odyssey”s Jarvis has a decided advantage. In the early twentieth century it was believed that Mars’ atmosphere was thin, but not necessarily beyond the range of human adaptability. After all, settlements on Earth exist at altitudes of up to 5000m, where the atmospheric pressure is less than half that at the surface. Thus Weinbaum speaks of “months spent in acclimatisation chambers”, but otherwise frees his explorer from the needs of atmosphere management [2].

By the mid-1960s, Earth-based observations and the first of the Mariner probe missions had removed any doubt about the hostility of Mars’ atmosphere. Robinson Crusoe on Mars’ Kit Draper was reliant on bottled oxygen to survive, and this was initially a serious threat to his survival. Fortunately he stumbled across abundant scattered rocks which released oxygen and flammable gases when heated. He was able to use these to recharge his oxygen cylinders and ultimately to pressurize a cave habitation. In all honesty, though, this is best treated as a narrative convenience. While a variety of chemical processes do give up free oxygen, these rarely involve baking. Oxygen bonds strongly to other elements and it is rarely energetically favourable to break these bonds. The process of heating materials generally involves the process of oxidation in which oxygen is consumed and tied up chemically in the products, rather than the reverse. There is also no discussion of how Draper avoids excessive carbon dioxide build-up - a perpetual problem in a CO2-rich Martian atmosphere.

However, while simple heating is not likely to be sufficient, that does not mean oxygen cannot be released from Martian rocks. Experiment has demonstrated that oxygen can certainly be released from moon rock with a careful arrangement of electrical currents, and this would be feasible on Mars with a more advanced technology than the simple methods of Robinson Crusoe on Mars. Similar electrolysis of water is used to generate oxygen on the International Space Station, and NASA has recently demonstrated oxygen generation on Mars using a small device on the Perseverance rover.

By 2015 this was well understood, and The Martian’s Mark Watney is fortunately supplied with an abandoned habitation module fully equipped with an “oxygenator”. This is an electrolysis-based device which is indeed capable of splitting oxygen from carbon dioxide, rocket fuel or other materials. As a result, oxygen supply is relatively low on Watney’s list of survival concerns.

Water to Drink

Perhaps the next most urgent demand for any human in a new environment is securing fresh water.

 Here again, Weinbaum’s stranded Jarvis had a distinct advantage. His shuttle is equipped with a water tank, which survives the crash, and he has only an 800 mile journey rather than an indefinite future to provide for. Without needing to deal with the weight of an oxygen supply, and benefitting from the low Martian gravity, he is able to simply take this water with him:

“Weighed about two hundred and fifty pounds earth-weight, which is eighty-five here. Then, besides, my own personal two hundred and ten pounds is only seventy on Mars, so, tank and all, I grossed a hundred and fifty-five, or fifty-five pounds less than my everyday earth-weight.” - Jarvis, A Martian Odyssey.

It’s also worth noting though that in 1934, the prospect of surface water on Mars - the famous canals - was far from abandoned. In addition to Jarvis’s personal supply he encounters a “a yellow trickle of water” flowing through the base of a canal, and also realises that his alien companion’s weapon was based on evaporation of a minute quantity of water stored inside it.

 By 1964, the Martian canals had been well and truly confined to the realm of myth, and the crash landed Kit Draper had a far more significant problem to overcome. Fortunately he landed near a mountainous region and here we see a possibility that was popular amongst areologists of the time and is still discussed: that substantial aquifers may still exist under the Martian surface. Draper struggles to eke out his limited water supply, until he follows his chimpanzee companion through a fissure in the rock and discovers pools of liquid, and apparently fairly warm, water deep in a cave system.

Unfortunately for our astronauts, we now know that while Martian caves are indeed a promising source of water, it is likely to be frozen solid. Liquid water may exist at high pressure beneath the frigid Martian icecaps but over the bulk of the planet the sheer cold will penetrate deep underground, and unlike Earth, Mars appears to have no residual volcanism capable of melting it. As a result, 2015’s Martian Mark Watney must resort to more technical means. Initially collecting and filtering his own urine, when he requires larger volumes of water he is able to generate it by a chemical process. Oxygen (O2) from his oxygenator is burnt together with a stream of hydrogen (H2) generated by a simple room temperature electrolysis from a supply of hydrazine (N2H4) rocket fuel. The result is an abundant rain of water (H20) in his enclosed habitation module. As ingenious and plausible as this procedure is, it has to be acknowledged that Watney was fortunate in his resources: both a supply of spare rocket fuel and the chemical knowledge required. Given the explosiveness of both pure oxygen and pure hydrogen, he was also very fortunate not to destroy himself entirely!

Food to Eat

Equipped with air and water, our astronauts next needed to consider food to eat.

The idea doesn’t seem to have bothered Weinbaum’s Jarvis, who had the good fortune of a well-stocked supply base to which to return [3]. Our other astronauts, on the other hand, faced a bigger challenge. Having located warm water pools, it should perhaps not be too surprising that 1965’s Robinson Crusoe on Mars was fortunate enough to locate a floating bladder-like plant which proved edible, first to the chimpanzee and then to Draper himself. Showing a little more enterprise, and imitating his earth-bound predecessor, he quickly creates a series of shallow pools and begins to successfully farm the plant, using its fibrous stems as rope and for fabric as well as its bladders for food, and thus exhibiting an essential trait for survival in marginal environments: utilisation of every aspect of a resource rather than permitting waste. The nature of the plant is never really discussed, but it is interesting to speculate: by the 1960s it had long been realised that only very simple life, such as algaes or lichens might exist on the planet, and the weed resembles a form of kelp or similar algal sea-weed. As a cave-dweller, it cannot derive its energy directly from the Sun but might plausibly have utilised a form of chemical energy production, such as that seen in ocean vents on Earth, based on its underground thermal pool environment. Again, this now seems implausible, and would already have been considered speculative by the mid-1960s, but it is not beyond the realms of even modern scientific speculation and shows consideration given to telling the story in a scientific context.

(Image above: Draper's successful cave-protected aquaculture using natural thermal spring water in Robinson Crusoe on Mars (1964). Left: Watney's effort at Martian potato agriculture, showing also the fuel-burner which generates water inside the Hab, from The Martian (2015).)

Again, The Martian’s Watney has the toughest draw in this lottery. But as a botanist, he was perhaps uniquely suited to maximising the potential of his resources. With native vegetation of any sort on Mars now considered implausible, the only plausible source of food is the limited supply brought from Earth, and this was unlikely to sustain him until rescue. While most of that food was highly processed, Watney identified viable growth buds (eyes) on a supply of potatoes carried for special occasions. He collected Martian soil, fertilising it and supplying it with a microbiota from human waste, and was able to begin farming a crop of potatoes which will keep him supplied with food:

“They grew even better than I had expected. Mars has no insects, parasites, or blights to deal with and the Hab maintains perfect growing temperature and moisture at all times. They were small compared to the taters you’d usually eat but that’s fine. All I wanted was enough to support growing new plants. I dug them up, being careful to leave their plants alive. Then I cut them up into small pieces with one eye each and reseeded them into new dirt. If they keep growing this well, I’ll be able to last a good, long time here.” - Watney, Sol 65, The Martian.

While this venture ultimately ends in failure, it significantly extends Watney’s possible stay on the planet. Potatoes are well known as a good pioneer crop - capable of breaking up and enriching a soil while tolerating low light conditions. Indeed, they have been grown in Mars-simulation environments, such as the Arthur Clarke Mars Greenhouse in northern Canada. However this scenario is not without its problems: potatoes tolerate low light but grow better in bright sunlight. They are also tender plants, sensitive to temperature swings which would be a constant problem on the planet. As writer Weir has acknowledged since, Watney would also need to use some of his now-abundant water to wash toxic chemicals (perchlorates) from the Martian soils before attempting his experiment. Nonetheless, the fiction here was both inspired by and has inspired in turn ongoing work on feeding a Martian settlement with in-situ resources.

Heat and Shelter

With the basic needs of our astronauts supplied, it is perhaps time to consider their need for heat and shelter.

 Curiously enough, it’s possible that 1934’s Dick Jarvis has the short end of this deal. Stranded on the planet’s surface he seems to be singularly ill-equipped in this respect. While he appears able to exist on the surface during the day time with little or no protection, at night, he: “got into my thermo-skin to sleep. The fire hadn't kept me any too warm, but that damned sleeping bag did. Got stuffy five minutes after I closed myself in. I opened it a little and bingo! Some eighty-below-zero air hit my nose, and that's when I got this pleasant little frostbite to add to the bump I acquired during the crash of my rocket.”

 Of course, by 1965, it was clear that conditions, even in the Martian daytime, were far beyond the limits of human survival. Commander Kit Draper was equipped with a thermal pressure suit, but ultimately lucked out and benefited from the same cave system that supplied him with food and water. The thick walls of the cave provided insulation, areothermal energy provided heat, and ultimately Draper was able to pressurise a cave to provide a permanent residence.

This was both a harder and an easier struggle than 2015’s Mark Watney. Watney was left with a fully-equipped, solar powered habitation module (“The Hab”, see image left) designed to support six astronauts for 31 Martian days (or sols). As the rest of the crew had evacuated after 18 days, and the equipment was designed with spare capacity and lifetime, heat and shelter was not really a challenge for Watney. On the other hand, the Hab was a surface habitation, relatively small, fragile, subject to storm damage, pressure imbalances, and thermal fluctuations during the day/night cycle. Although it has thick walls, as can be seen in the image, which presumably also provided thermal insulation, it would also be exposed to the substantial flux of radiation which penetrates Mars’ thin atmosphere. Given the need for transparent panels overhead in the Hab, this radiation threat might be significant.

As a long term habitation therefore, it would have significant drawbacks and would potentially leave Watney vulnerable to cancer or other dangers of the Martian environment. Indeed, many researchers are now seriously considering underground or cave settlements as preferred sites for human settlement on Mars. For all the difficulties of pressurising fissured rock, Draper’s cave walls would provide far more radiation protection, and hence long-term viability, than Watney’s more technically advanced habitation!

This has just been a quick look at a few of the many examples of astronauts stranded in hostile environments in science fiction. It by no means covers all the many and varied resources that a long term human settlement would require to survive. But it does give a little insight into the ways in which science fiction can capture our changing scientific knowledge of our neighbouring planet, and the ways in which it can act as a thought experiment which may ultimately inform the science of the future.