How high a priority should we have for sending people to Mars? This seems to be a big question these days. NASA is developing the Space Launch System (SLS) and the Orion capsule specifically to have the capacity to send people to Mars. Elon Musk has stated that the real purpose of SpaceX is to colonize Mars.

The public imagination has also been sparked by movies such as The Martian (which was excellent). I also recommend National Geographics’ series “Mars” which is a combination of interviews with current scientists and engineers about the problems that a Mars colony would face, with a narrative about a future colonization mission.

The one fact that everyone agrees on is that colonizing Mars will be extremely difficult. Mars has an atmosphere about 1% that of Earth. This makes it just thick enough to be a problem but not thick enough to help with breaking while landing on Mars, and not thick enough to make the surface any more livable. A 1% atmosphere is effectively a vacuum, but it is enough to cause planet-wide dust storms that would make life on Mars challenging.

Transfer to Mars would take about 8 months with current rocket technology. Depending on the relative position of the planets and the transfer speed, 130-260 days are the figures most often cited. That means supply lines would be very difficult, and don’t expect any rescue missions.

If there is life on Mars, it is microscopic and would not help sustain a colony. Colonists would have to jump start a greenhouse ecosystem. They would also need water, oxygen, and energy. There is also the problem of radiation exposure, which would require highly shielded or underground facilities.

Can we create an atmosphere?

Many of the challenges of colonizing Mars would be solved if we could just thicken its atmosphere. An atmosphere close to the density of Earth’s would make facilities easier to build, since they would not need to be pressurized as much. Leaks would not be as catastrophic (no explosive decompression). An atmosphere would also warm the surface of Mars and protect the surface from radiation. It might be theoretically possible for colonists to walk on the surface of Mars under an atmosphere without a spacesuit, just with a supplemental oxygen supply.

Creating an atmosphere on a planet, however, seems like a daunting engineering problem – and it is. We know that Mars had a thick atmosphere in the past. Under the ancient Martian atmosphere, Mars was warm enough to have flowing water on its surface. However, over the intervening billions of years Mars lost most of its atmosphere due to solar winds.

There is a constant wind of ionized particles coming off the sun. The Earth is protected from this wind by our magnetic field. The ionized particles move along the magnetic field lines around the Earth. Occasionally, if they are strong enough, they dive down into the atmosphere at the magnetic poles, resulting in the Northern or Southern lights.

Mars lacks a planet-wide magnetic field. (It has small regional magnetic fields which are too weak to protect the atmosphere.) For this reason, over the years, the solar wind has slowly eroded away its atmosphere. The crust of Mars has also long since solidified, so there are no more volcanic eruptions to replenish the atmosphere.

If we are going to seriously terraform Mars, and give it back an atmosphere, there are therefore two things we can do – we can find a way to add gases to thicken the atmosphere, and we can find a way to increase Mars’ magnetic field. The former may be easier than you think. The poles of Mars contain frozen water and carbon dioxide. Raising the temperature on Mars would have a runaway effect because it would start to melt the poles, which would add more CO2 to the atmosphere, raise the temperature, which would melt the ice at the poles even more.

We don’t know exactly what Mars would be like at this point. We do know the water would cover vast areas of Mars meters thick, but that is substantially less than the water content of Earth. The atmosphere would be almost entirely CO2. There would likely still be some ice at the poles during winter. We could start converting CO2 into biomass and oxygen, but getting a breathable atmosphere would take about 1,000 years.

Adding additional volatiles to Mars could help. We could, for example, redirect icy asteroids to collide with Mars. Ideally we would complete this process before putting any colonies on Mars, and such a project could take centuries.

All of this would be temporary, however, as long as Mars still lacks a magnetic field. The water and CO2 would eventually get blown away by the solar wind. Even still, if we could make Mars livable for a million years, we can worry about the the long term effects later.

There are those, however, who think that if we could find a way to create a magnetic field on Mars that would help with everything. It would protect the surface from radiation to some extent, and protect any atmosphere we release on Mars. Creating a planet-wide magnetic field, however, is no easy task.  NASA, however, is thinking about doing just that:

At The Planetary Science Vision 2050 Workshop at NASA headquarters, Jim Green – NASA’s Planetary Science Division Director – is proposing launching a magnetic shield to do just that.

This is in the pure speculation phase, but it is an interesting idea. Details are sketchy at this point. One idea is to create solar-powered magnetic coils in orbit around Mars. These would be huge, and there would have to a lot of them to surround the planet. This would be a non-trivial engineering feat.

Once in place, however, it would make it easier to build up an atmosphere on Mars again.

All of these ideas for Terraforming Mars are interesting, but they are for the long term. This century, if we are going to go to Mars, we will have to deal with its harsh environment. There is no reason why we cannot do it. It will just be expensive and difficult, but existing technology could theoretically get the job done.