Objections to Mars Colonisation

A summary of bad arguments that keep being repeated

When people who are either uninterested in space colonisation, or actively opposed to it, comment on the prospects of travelling to Mars they often make the same or very similar arguments, unaware that these arguments were either ill-formed to begin with or have already been convincingly refuted.

What I want to do here is have a quick, easy to reference list of such arguments that can be shown to those who make them. There are other resources for more detailed answers - such as Casey Handmer’s blog which cover some of the same ground as these questions, and my own posts elsewhere on this blog.

I welcome corrections and submissions to this page. Please comment below or contact me on Twitter.

A future page will cover objections to space colonisation in general; to get this and other space content in your inbox, please consider subscribing:

“Humans can’t live on Mars because it lacks a magnetic field”

The core of Mars no longer produces a significant magnetic field the way the Earth’s does. The Earth’s magnetic field deflects some of the particle radiation coming from the Sun and from outside sources (galactic cosmic rays) and protects our atmosphere from being stripped away by the solar wind.

The lack of such a field on Mars is by no means a showstopper for colonisation, however. The main protection we have from cosmic rays on the surface of Earth is not our magnetic field, it is our atmosphere. For ballpark figures, the shadow of the Earth screens about half the radiation out for us, and the magnetic field stops about a third of what’s left. Most of the remaining two thirds is attenuated by the atmosphere. So astronauts at the ISS experience an annual dose around 200mSv, around 100 times typical surface levels.

The lack of a magnetic field on Mars does mean that its atmosphere is being constantly stripped into space. This is commonly cited as a reason that terraforming can’t be done (see question below) but the rate of atmospheric loss is very slow. Far slower, in fact, than the rate we currently add mass to the Earth’s atmosphere through our carbon emissions.

The measured loss rate of Martian atmosphere is 1-2kg per second. Each year, the UK alone emits 405 million tonnes equivalent CO2, of which 79% is actual carbon dioxide. Taking the carbon content of that alone (3/11 of the total mass) that means the UK is adding around 2,700 kg of mass to the Earth’s atmosphere per second. Replenishing Mars’ atmosphere, if necessary, would thus be fairly trivial.

“Humans can’t live on Mars because terraforming is impossible/impractical/takes too long”

It’s a fairly common argument to try and equate Mars settlement with terraforming. That nobody can or would want to live on Mars if it were not perfectly Earthlike. From this jumping off point, its fairly easy to criticise terraforming the planet; if possible it would be the grandest endeavour of humanity by a large margin.

Realistically, the choice to terraform and how to do it would require a great deal of knowledge of the planet as well as technology, and thus is best left to the residents of the planet to decide on. So almost by definition a colony is required before terraforming can even be contemplated. Certainly sending humans, even permanently, isn’t going to wait on the planet being transformed.

We simply don’t know enough to say if it can be done, anyway. Recent studies about the projected CO2 inventory of the planet do not restrict the final atmospheric pressure because oxygen from rocks can be used as a substitute. Post terraforming temperature can’t be guessed from this CO2 inventory either because it doesn’t consider the use of space mirrors or manufacture of stronger greenhouse gasses. It’s too soon to declare terraforming impossible, and in any case its not required for colonisation.

“Humans can’t live on Mars because they have to live underground and would go crazy”

This argument notes the lack of a thick atmosphere to stop galactic cosmic rays (GCR), notes that the surface dose exceeds what is considered safe for adults on Earth at the moment and definitely exceeds what is safe for children, and concludes that any Martians would have a miserable existence living in a cave for the rest of their lives.

What this argument fails to consider is the geometry of the atmosphere. GCRs entering at shallower angles have to pass through significantly more atmosphere than those entering at steeper angles. A NASA study of surface radiation showed the atmospheric shielding at zenith is about 20g/square centimetre, which does very little. Towards the horizon however it is over 300g/square centimetre, which is more than you get at zenith on Earth when flying in an airliner. A thick, overhanging roof on a building or habitat can reduce radiation inside to safe levels, whilst allowing thin windows at the sides to allow in plenty of natural light, and not requiring excavation.

Some underground areas might be useful - I used a mix of underground and surface habitats in my proposal of the Mars Society city state competition - but this is far from the cave dwelling envisioned by critics.

“Humans can’t live on Mars because perchlorate in the soil will poison them”

This is another objection that seems to stem from the proposer imagining an intentionally badly designed Mars colony. The notion is that people will come in from EVAs, tread regolith through their habitat, and just toss their dirty space suit in a corner somewhere. On Earth we already have a mature technology for clean rooms, and we regularly use foot washing stations to stop biological contamination being spread to farms during outbreaks of disease such as foot and mouth. It is a stretch to imagine that its beyond our capability to prevent raw regolith getting into our Martian farms.

There is also the implicit assumption in this objection that perchlorate is a persistent chemical that is hard to get rid of. It is not - its incredibly reactive, so much so that it is the oxidiser component of solid rocket fuel. Experiments on Earth have found that water alone can be used to remove these highly soluble salts, and scientists have successfully grown and eaten plants produced in soil decontaminated in this way.

“Humans can’t live on Mars because 38% Earth gravity has such terrible effects”

We do not really know what impact Martian gravity has on humans, and to be fair this is probably the biggest potential problem for colonisation. However, when this argument is presented as a definite and impenetrable barrier to colonisation, it usually refers to the effects of weightlessness on humans, and just assumes that these will also manifest on Mars.

No human has ever been exposed to Martian gravity. 12 white American males with very similar careers, ages and backgrounds have been exposed to lunar gravity for a day or two each, which in terms of medical studies of the impact is essentially useless for multiple reasons. We have effectively zero data on what happens to humans between 0g and 1g. There are ongoing animal studies in a centrifuge on the ISS, and we await the results

“Humans will never settle Mars because we haven’t settled Antarctica”

I have done an entire post on this - but here is the short version. Compared to Mars, Antarctica is energy poor, has a very difficult day/night cycle, is protected by treaty from serious colonisation, and does not give advantages for reaching other places.

Mars, with its relatively weak gravity well, allows easier access to the rest of the solar system than the surface of Earth. This also applies to the Moon - but the lunar environment is very harsh even compared with Mars.

It has also been pointed out to me that Antarctica has, in fact, already been colonised - albeit at small scale. So the objection is incorrect in its basic premise.

“A Mars colony cannot work, because Biosphere 2 shows that we can’t create an artificial biosphere”

Biosphere 2 was an attempt at a closed-cycle bio-regenerative habitat which in the early 1990s conducted two experiments where crews were sealed in the facility for an extended period of time. The first experiment suffered problems maintaining sufficient oxygen levels and growing enough food, which led to them needing to introduce oxygen from the outside to keep the crew healthy.

The argument goes, roughly, that ecosystems are so complex that this kind of event is inevitable, and that it being inevitable means that any attempt to create a closed cycle life support system on Mars is doomed to failed - alongside the whole enterprise of Mars colonisation. This argument falls down on several levels

• The second Biosphere 2 experiment went a lot better from a technical perspective. It was terminated early due to management issues in the company unrelated to the content of the experiment itself. Its a complicated story, and Steve Bannon ends up in charge at one point. Yes, that Steve Bannon.

• The standard of a life support system being 100% is not a sensible target. So what if a Mars colony has to introduce additional oxygen? Oxygen is not hard to manufacture through industrial processes. It can even be made on Mars - we know, because its already been done.

• The experiment was overly complicated and poorly designed. The creators were not scientists, and were following ideas about ecosystems that were even at the time not really taken that seriously. Biosphere 2 contained different biomes matching the biomes of Earth, and contained thousands of species of plant and animal. Early Mars colonies will take a simpler approach, and build up from there.

• Even if 100% closure of the life support system on Mars cannot be achieved with a combination of biology and chemistry, It doesn’t need to be. So long as whatever Mars exports (and this can include stuff like patents and real estate titles) can pay to import the deficit from Earth, the colony is as sustainable as any other nation on Earth that relies on trade (i.e. almost all of them)

• There have been better designed and far more successful closed cycle life support system experiements. BIOS-3 in Russia and the more recent Lunar Palace experiment in China - which despite being still dependent on some elements being imported due to its evolving design, was able to achieve over 98% closure and manage gas levels well.

Overall, Biosphere 2 is being used in this argument as a sort of fable about the dangers of scientific hubris, without much knowledge of what actually happened there, what its salience was, or how other experiments in regenerative life support systems have turned out.

“We cannot colonise Mars because it would be impossible/unethical to raise children”

Firstly, it should be made clear that having children on Mars is not a priority immediately after landing. As well as requiring a well shielded habitat due to the higher sensitivity of children and pregnant women to radiation, a settlement would have to reach a level where it could spare the large amount of labour require to raise a child - and for a while after landing it will likely require everyone engaged fully in the tasks of survival and base building.

The main challenge would be the impact that reduced gravity would have on a child. I’ve addressed this objection for adults above - but its an extra concern for children as there is the question of how their muscles, bones and circulatory system would develop under reduced load. I’ve heard this described as an unethical scientific experiment to perform on children - but realistically, many people’s children are born into what could be considered suboptimal conditions. Some children spend too long sitting in front of a computer, or don’t have gardens to run around in. Some children eat too much junk food. The idea, though, that a persons decision to have a child or not could be vetoed by some ethics committee is deeply illiberal. Occasionally a politician may float the idea that this can be applied on Earth, but its rightfully rejected by almost everybody when they do.

We definitely should do animal experiments to discover these effects beforehand, and likely will both on the surface of Mars and in Earth orbit using artificial gravity. Martians will only have children with some understandings of the risk, and the choice to become parents or not in the context of these risks is theirs alone.

“There are better places in the Solar System to colonise”

Some of those who are in favour of space settlement in general oppose Mars in particular for various reasons. This may combine with the objections above. Generally the answer to each of these would be the same, but its also worth reviewing why other proposed locations are not better

1. The Moon is a much more hostile environment than Mars, with no atmosphere at all, huge temperature variations, a long day-night cycle and a shortage of resources for life and civilisation. Its merit is its proximity - real time communication is just about possible (with a noticeable delay of about 3 seconds round trip) and return to Earth is possible at any time in a few days. These properties may make it an appealing test site, but not a long term colony

2. Titan is very, very cold and energy poor due to being far from the Sun. Its surface atmospheric pressure is about 50% higher than Earths which means that a full spacesuit might not be needed - just an oxygen supply and really, really good insulation from the cryogenic temperatures. It does have interesting chemistry - lots of carbon compounds - but its hard to understand how a world so far from the Sun can be a viable near term target for colonisation

3. The upper atmosphere of Venus, at about 50km above the surface, has Earth-like pressure and temperatures close enough to that of Earth to be considered friendly by solar system standards. In the dense atmosphere of the planet, the oxygen/nitrogen mix we breathe is a lifting gas, and therefore our colonies can float at this altitude. The gravity there is also almost the same as that on Earth, and very likely would have no ill health impacts. On the face of it, a very promising location. Alas, floating in the atmosphere leaves such a colony stranded from resources - no metals to mind for instance. It also places them at the bottom of a very steep gravity well, which is hard to get out with and thus trade with the rest of the solar system for what they need. Such colonies would thus never be self sufficient and probably be limited to being scientific outposts.

4. Free space colonies such as O’Neill cylinders are very strong contenders - and indeed in the long term I do agree that these would be better places to live than the surface of Mars. They can have an entirely customised environment including gravity levels, and the scope for expanding them is limited only be the resources of the solar system. However, they are very massive - basic designs start at millions of tonnes - and require infrastructure in place on planets before they can be built. In The High Frontier Gerald O’Neill proposed building an industrial base on the Moon to construct these. Mars can be colonised as a single step, without any preliminaries and without needing millions of tonnes of space resources under our control before humans go there. We have to start on planets, and Mars is the best planet besides Earth.