Congratulations to the great Elon Musk, whose Dragon capsule has successfully docked to the Space Station for the second time. SpaceX is moving along in leaps and bounds. Musk has long since stated that his ultimate goal is to successfully land people on the planet Mars. I fully believe he will accomplish that goal. He has even said that he would like to get the cost down to around half a million dollars, which would make moving to Mars a realistic goal for millions of people. I know that if I had the money, and he had the spacecraft, it’d be a tempting offer.
So when humans get to Mars, obviously the first priority would be survival. Mars is a hostile place. It is a freezing -60°C, there is no oxygen, and the atmosphere is only 1% the pressure of Earth’s. Clearly, we will be living indoors. Moving around outside would be possible with the use of pressure suits and oxygen tanks, but the cold would present a real challenge. Most of the energy produced would be used in just keeping us warm.
Once the first colonies are established, what should the next focus be upon? I think that attention should be turned to making the planet more hospitable; more amenable to life. The reason Mars is so cold is simply that it is further from the Sun. Obvious it can’t be moved closer, but that’s not the only way a planet can be warmed. Everyone is aware of the crisis currently facing Earth – global warming. This is a problem here because we are already at an ideal temperature for life. But on Mars there is plenty of room for warming!
Contrary to what you may think, global warming on Earth is driven largely by water. The water vapor in the atmosphere keeps the earth around 30°C warmer than you would expect for its orbital dimensions. Water is a very weak greenhouse gas, but there is such an enormous amount of it that the overall effect is powerful. Carbon dioxide is much stronger, but there is much less, and so the effect is weaker (but still significant!) Following on, CFCs are very powerful greenhouse gases, but are present only in tiny volumes.
Now this is understood, and we want to go about warming Mars, what greenhouse gas would we use? Obviously, on a newborn world, we have limited resources. We simply don’t have the volume of water or carbon dioxide that we need to replicate the effect as it happens on Earth. What we do have are rocks. Lots of rocks. What can we make from the available resources? If we put some figures to the global warming potential (GWP) of the candidate substances, a clear choice emerges. Giving carbon dioxide a reference GWP of 1, water has a GWP of less than 0.1, methane has a GWP of around 25, nitrous oxide around 300. Impressive, but still not efficient enough. CFCs pack a powerful GWP of around 5000. We can still do better. A substance called sulphur hexafluoride (see videos of its amazing properties here and here) has a GWP of 23,000. That is, for every 23 tonnes of carbon dioxide in the air, you would need only a kilogram of sulphur hexafluoride. Much more efficient!
Moreover, sulphur hexafluoride is easy to produce. All you do to produce it is heat sulphur and fluorine together. Sulphur and fluorine are widely available all over Mars. Sulphur hexafluoride is non-toxic, unreactive and stable, and is a very dense gas at -60°C, so will cling to the surface, where heating is needed most. As Mars warms, the huge amounts of frozen carbon dioxide and water will both melt and enter the atmosphere. Mars will become warm and with a comfortable pressure. Our colonists will be much more comfortable.