Mars has always fascinated the humanity, who has sent many sounding lines with the purpose of knowing him better. Some years ago, Curiosity, a spacial sounding line sent in 2012 with the purpose of investigating of what it is composed, discovered evidences of water in the red planet.
This discovery indicated that, millions of years ago, Mars was a very good candidate for the alien live. During a long period of time, Mars would have been a planet with oceans that recovered the hole Martian surface with some meters of depth. But now, this water has been lost and the planet is formed by big quantities of sand and rocks. It has a very arid surface on which there are normally very big sand storms that can arrive to recover the hole planet.
Nevertheless, other sent sounding lines show us images in which we can see big frozen water surfaces, whereas in the poles and in the subsoil, that, how the Curiosity found out, it could have a 20 kilometres lake made of liquid water. But, apart of this small lake, there are many others with frozen water. This water could have, if we defrost it, a similar water volume of the Earth, which could be used in different finalities.
One of this could be provide a future civilisation that would live in Mars from this water, and like this, there would be no reason to send rockets to Mars filled with water.
Another one would be decompose the water into hydrogen and oxygen. The hydrogen could be used for the production of combustible for spacial ships that would go to further planets. By doing it this way, the spacial ship that leaved the Earth would only carry combustible to arrive to Mars, and then, from the red planet, we would fill again the deposit.
The oxygen could also be used, we could fusion it to form dioxygen, which it is two atoms of oxygen which have been fusioned. This is what we breath in the Earth. First we should fusion the oxygen, and then we could breath, because, the oxygen alone, is a very bad gas for our health, but, if it is fusioned, it is essential for us to live.