Why Mars?

Its very common for people who are unfamiliar with the arguments for space colonisation to suggest that its ridiculous on the face of it that humans can move to Mars and live there. They typically cite the fact that there are no permanent residents in Antarctica as proof of this.

Here is a good recent example of the argument, from an international affairs columnist.

The CEO in question is obviously Elon Musk and this refers to his intention to establish a city on Mars. This tweet is presented as if its an irrefutable knock-down argument. The rather condescending tone of it, as if this were the most obvious thing in the world and space advocates were simply dumb for not having thought of it, is a hazard when you don't bother to check if there is already a response to your argument before you publicise it. I don't mean to pick on this one person - but his argument is so very common it is worth having a rebuttal to hand.

There are many good personal reasons to go to Mars - exploration, adventure, the opportunity to start a new branch of human civilisation - but that isn't really the question at hand here. What I think it boils down to is why building a Mars settlement is rational (or not) from a civilisational perspective. It very much is, and I can explain why.

Antarctica is Poor

The Earth presents to Sun a surface of 128 million square kilometres, allowing it to capture 174 million gigawatts of energy continuously. We harvest a significant portion of this - about 30% of the ice free land area of the planet - through agriculture in order to drive our civilisation. We collect some through solar power, recover ancient solar energy through fossil fuels, and harness winds driven by the Sun's power. Three forms of energy not directly dependent on the Sun - geothermal, nuclear and tidal - are very marginal in comparison to agriculture. We are to a good approximation a solar power civilisation.

Antarctica is incredibly poor in solar energy. The Antarctic Circle fairly approximates the continent of Antarctica, and the surface area the Antarctic circle presents to Sun at equinox 1.8 million square km, less than 2% of the total cross section area of Earth. At the southern summer solstice that briefly rises to around 6%, whereas at the winter solstice it receives no direct sunlight at all. The equinox approximation is good enough as a time averaged value for this calculation though.

The Earth as seen from the Sun at equinox, with the Antarctic Circle marked

Solar flux at Earth's average orbital distance is 1.36 gigawatts per square kilometre, whereas at Mars it is only 0.59 GW/km2, with Mars varying more than Earth due to the eccentricity of the planet's orbit. Even taking this lower insolation into account, Mars gathers about 10 times as much energy as Antarctica, and crucially for most of the planet the intermittency of this energy isn't nearly so bad. As on Earth, at most latitudes the night lasts hours rather than the months of darkness experienced in Antarctica.

Mars captures about 12% the energy of Earth - or about 40% of the energy of Earth's land area. This would represent a significant boost to our potential civilisational capacity, even though we would not use it all. It might be tempting to think that unused areas of Earth besides Antarctica might provide a similar energy harvest, but the problem there is with the notion of what is really unused.

Seasteading may allow more energy capture without leaving Earth - but it suffers from a lack of raw materials besides those found in seawater, and its questionable how much independence such settlements would really have. Such independence they do have may legitimately be questioned if seasteaders start to have an impact on the marine environment - because the energy that falls on the sea is already in use, by the biosphere, and much of the Earth's population think that is the best use for it.

Sometimes the Sahara or Gobi deserts are cited as alternative locations. These deserts are all in existing countries, and therefore not really subject to new human settlement without either submitting to the authority of these countries or fighting them. Also, like the sea, these places are ecosystems and not blank slates that the rest of humanity will automatically be happy with settlers exploiting.

In one respect, we are already a Kardashev type I civilisation - one that uses all the energy available to a planet - because we place nonzero value on the natural environment and thus, to a less or greater extent, use every photon of sunlight that falls upon the Earth to support it - and because when we do not divert this energy to industrial purposes it is purely by our choice and has been so since the mid 20th century, when all of the surface of the planet became reachable.

Mars and Beyond

I can thus summarise what the unique appeal of Mars is, from a dispassionate economic perspective:

Mars offers lots of unused energy impinging on raw materials we can easily use, at a location where accessing more energy is much easier.

This latter part is important because Mars is not the final destination. Thinking in terms of energy capture as I do leads to an O'Neillian conclusion that humanity should ultimately live in free floating habitats. The total surface area of solid bodies in the solar system is just too small if we want to really start exploiting our home star. However, in the near term, we need to live near the resources that we require. The industrial revolution started near the coal supplies for a good reason, and the costs of transporting raw materials must figure into our plans for space settlement. Our current technology, more or less, will let us work with the materials present on Mars to continually expand our presence there, and problems such as gravity and radiation shielding are easier to solve on a planetary surface.

Once a branch of human civilisation is established on Mars, it can much more easily access the remaining energy of the solar system - the escape velocity of Mars if only 5km/s compared to 11.2km/s for Earth. Placing our industry in a shallower gravity well thus has substantial material benefits that cannot be found anywhere on Earth.

Looking at Mars this way also explains why other colonisation targets should not be as high priority - Ceres has an even lower escape velocity than Mars, but is far from the Sun and small so is energy poor. Venus gathers more energy than even Earth, but the part we could possibly inhabit, the tops of the clouds at 50km altitude, lack many resources and the escape velocity is almost as high as Earth's, never mind the extra velocity required to then get out of the deeper part of the Sun's gravity well. Our Moon has a low escape velocity and captures a fair amount of energy - but the two week nights for most of its surface make it challenging to exploit, and it seems to be short of some key volatile elements. For that killer combination of energy, raw materials, and ease of access - Mars is the place.

This shows Mars is a promising prospect for expanding our energy capture and material resources. There are some making the case that this in itself is a bad thing - but if people are making such a case they should do so openly, and admit what it really means for human wellbeing, rather than throwing around cavils about Antarctica.

For the rest of us, who wish to see humanity continue forward, improve our material well-being and accomplish ever greater technological feats, there is no reason to wait, and certainly no net benefit in carving settlements out of the remaining wildernesses of Earth. The sunlight that does not strike the Earth outweighs the sunlight that does strike it by a factor of 2 billion, so even if we ultimately could not capture more than 0.1% of this, it would still support a population of 16 trillion humans with a per capita energy consumption (including supporting biospheres) 1000 times greater than we currently have. The smallness of current terrestrial civilisation compare to a potential solar civilisation means that this planet will ultimately diminish in significance, and all of its history will be a mere prologue to the larger history of humanity. The day when we establish our first settlement on Mars will be the beginning of Chapter One.