As many scientists said before humans existence is not linked only by this planet but with its continuation to other locations in space. There are disturbingly numerous causes of total annihilation for human specie as giant meteor/comet collision, unstoppable pandemics, nuclear wars and others. This is just one of the reasons that humans would have to consider leaving planet Earth in the future, not only for survival but for massive expansion through out the Universe. Colonizing planets or even Terra-forming them would be an important asset in this mission, as planets or other space objects can be used as base operation for in depth space expansion and exploration.
Without doubt the first two space objects which humans will have to use to build space stations on them are Mars and Earth's Moon. But Mars although more distant than Earth would probably provide the biggest assets as it is the most closely related planet to Earth in our Solar System. Its atmosphere is more dense and provide more protection from radiations and micrometeorites, its gravity is more powerful than Moon and more similar to Earth, at its poles on Mars was discovered ice and from this maybe in future missions water will be extracted. There are scientists that also think to transform Mars into a second Earth using for example greenhouse gas such as carbon dioxide to increase the temperature of the atmosphere. So Mars will be surely the first candidate on Terra-forming.
But more difficult tasks rise from the lack of space technology humans have and also their weakness in front of the enormous physical and psychological challenges a mission to Mars would demand. Also there are enormous costs for equipments and research. On space there are dangerous radiations that can endanger human life. In a mission outside our atmosphere an astronaut said that he could not sleep due to the radiations and micro-particles that interact with his retina and so even when he was trying to rest he saw sparks and lights. On Mir cosmonauts chose to sleep near some lead batteries to shield their head from radiations.
And this can be just a clue of how much quantity of radiations can exist in space. So the ships would surely have to use some extra space for radiation shielding, fact that will complicate the things even more. The psychological issues can arise when people are stuck in small places and even for large periods of time as a Earth-Mars travel. From past experiences astronauts can become anxious, nervous and can even start fights between them.
After spending a lot of time in just a single cramped place astronauts can simply became eager to finish their mission or escape some how from there which can lead to superficial work. They tend to skip important details and this can be detrimental for their activity. Even more bones and muscles tend to get weak losing mass during zero gravity so after a few months of space flight they can find themselves useless on the arrival on Mars.
Those are just a few of the colossal requirements that people must fulfill in their mission to Mars. But although almost impossible to achieve, this task would be surely completed in the future due to humans incredible resilience in face of challenges, as they proved this a long their entire history.
