Mars > Moon

I was going to wait until next week to write this one, but I got too excited.  So, here is post number two, a full four days early.

Some people will almost certainly wonder:  Why go to Mars?  If the main purpose is to get leibensraum, then the Moon offers a lot of good space to live, and is much cheaper and closer to home.  People on the moon might even be able to go vacationing on Earth!  Surely the moon is the logical first step.

Well, there are arguments either way, I suppose, and I fully approve of building moon cities as well as Mars cities, but I do think that Mars cities will be easier to build, easier to live in, and above all else, easier to sustain.  There is one very big reason for this: Air.

The moon has no atmosphere of any kind.  It is empty space straight down to the rock.  This presents a few unique challenges for colonists.  First, as a colony ship was descending to the surface, it would need to use thrusters (and therefore fuel) to control its descent.  There can be no airbraking, since there is no atmosphere.  That means that the landing craft will have to be designed far differently than our current aircraft, and have an increased fuel capacity, which will make them heavier, and thus more expensive, offsetting some of the cost difference between Mars and the moon.

Once landed, with no air on the moon, a colony will need to import its own atmosphere.  This is possible, of course, but difficult, and, as before, expensive, further offsetting the cost differences between Mars and the moon, but this will really cause problems when it comes to colony expansion.  Every time a settlement on the moon gets overpopulated, the people will need to get an air delivery from Earth before they can build a new settlement.  This means colonial development will be tied intrinsically to Earth, and population expansion thus strictly limited.  If the lunar colonies wanted to produce air of their own, they would have to mine it, and then chemically separate the various components from the rocks they dug up, a time consuming, and expensive process, and less effective than it would be even on Earth, since lunar soil is less oxidized, and has no organic nitrate contributions.  In short, just getting air to breathe would be a problem for generations.

Another issue is that on the moon, there could never be an aerodynamically based travel system.  No air, no airlines.  If ever the Moon reached a stage of development where there were multiple cities, all transit between them would have to be by train, or lunar buggy, because airplanes and helicopters simply wouldn't work, and travel by rocket is likely to be prohibitively expensive on a world where oil and accessible chemical fuels don't exist.  Hydrogen fuel would be possible, but creating it would have to be done at the expense of destroying the already relatively small lunar water supply (more on that later).  Not that trains are bad; they might, in fact, be better for the colony.  But the point is that flight on the moon would be limited only to rockets leaving, and landers coming in.

Mars, on the other hand, has an atmosphere.  This means that landing spacecraft can use drag chutes, airbrakes, and aerodynamically controlled flight to get where they want to go without needing extra fuel.  It means that Mars Airlines is someday going to be a possibility, and flying in to remote areas for exploration or rescue will be something that can be done quite cheaply.  The Martian atmosphere will need refining, but all the gases needed for Earth atmosphere are present, so making ourselves some breathable air will mostly involve mixing, not mining.  The atmosphere does lack oxygen, but it has abundant CO2 for plants, which can then synthesize the oxygen we need.  Turning rocks into air won't be very necessary.  As a result, a Mars colony could grow much more easily.

The issue of water will also come into play eventually.  Mars has substantial water reserves in the form of polar ice caps and there is also evidence of water permafrost, and even geological evidence of flowing water at some time in the past.  We can access water there by simply digging up and thawing the soil, and if we melted the ice cap we could cover the whole surface of Mars 5 meters deep (only the area, mind you; elevation was not included in this calculation).  The moon, by comparison, is extremely dry.  There is some water present, recently discovered in the deep shadows of polar craters, but the total estimates are only 500-700 million tonnes (I will assume that these are metric tonnes, though the article I was reading didn't specify), which is 500-700 billion liters.  For comparison, Earth currently uses about 6 trillion liters of water per day just to support humans (not including the water used by animals and non-crop plants), which means we would go through the entire water supply of the moon ten times daily.

Water can be recycled, but not quickly; much is trapped in the living organisms necessary to maintain a viable biosphere.  In short, we could expect, by harvesting all the easily available water on the moon, to supply drinking and irrigation water for a good sized city, perhaps even a few million people, with stringent water conservation laws.  The most water rich areas of the moon, even with the recent discoveries, are roughly as wet as the Gobi, a little wetter than the Sahara or Atacama deserts.  Whereas, on Mars, we could have swimming pools, showers, and hot tubs, and probably support a billion people comfortably with sustainable conservation measures.

On Mars, two of the biggest problems are expected to be the lack of a magnetic shield from solar radiation, and possibly dust storms.  As for the first, the moon has the same problem; either place, we will have to create a magnetic field of our own, or else develop some other sort of radiation shielding.  As for the dust, on that point the moon is a clear winner.  Mars sometimes has planet wide dust storms, which would frankly be terrifying.  However, the lunar victory on this point is not unqualified; solar wind does blast some dust up off the surface to play havoc with instruments and filters.  And, worse than that, lunar dust is electrically charged due to constant exposure to solar radiation, and will statically cling to any uncharged thing it touches, a habit which could cause problems.  So, while the moon won't have dust storms like Mars, a lunar colony will still have dust to deal with.

Lastly, the temperature.  On Mars, average temperatures range from -87 C (spit is ice) to 0 C (still cold, but bearable with a good stout coat).  You wouldn't want to go out and play, since you can't breath the atmosphere, but the variation is tolerable for most machines without too much redesign.  We've even measured -89 C on Earth, so life on Mars would roughly equate to life in Antarctica.  On the moon there is no air, so of course there is no air temperature.  But the surface temperature of the moon varies hugely, over 250 C, from above boiling on the light side to dry ice on the cold side.  Any equipment would have to withstand huge and rapid temperature fluctuations.

Now don't get me wrong, I think that colonizing the moon is a great idea.  In general, I am enthusiastic about colonizing pretty much any rock we can fly to, since the more places we go, the more we discover, and the more humanity can grow and learn.  Even today, I spent a good couple hours trying to figure out if kite colonies on Saturn, Neptune, and Uranus are feasible (All three planets have atmospheric regions where the temperature and gravity are roughly Earthlike, and the pressure is high (10-50 bar), but survivable with modern technology.  Neptune seemed especially promising, with a potential water belt right in the temperature zone I wanted.  However, the winds (1200 mph in some cases) made me conclude that though a giant kite or plane could fly there permanently, the turbulence would make the life of colonists very uncomfortable.).  But, whenever I think about where to go first, I think that Mars will be the easiest colony to land, the easiest to make permanent, and the easiest to expand using only local resources.

In short: Mars wins.