The most shocking pictures ever taken of another planet soon arrived. They involved the great Martian equatorial canyon. A canyon with a width of a hundred kilometers and a depth of 6 000 meters extending for more than 5 000 kilometers along the Martian equator: a structure that makes the Grand Canyon on the Earth look like a tiny cut. The axis of this depression probably formed as a result of the movements of the Martian crust. However, its borders are criss-crossed by many canals which, seen from the Earth, would certainly be recognized as river beds flowing towards the main artery. They have all the right features. If there are still any doubts about the origin of these structures, for others the analogy with Earth rivers is well beyond any doubt: winding courseways, well-defined banks, even river islands within the beds, with the characteristic droplet shape caused by the flow of the current. The presence of some freely flowing fluid in the past on the surface of Mars would thus seem to be beyond discussion. But we are on Mars, whose very thin atmosphere consists mainly of carbon dioxide and does not seem to be able to provide the abundant rainfall necessary to justify the presence of such massive structures. Therefore, scientists are still debating about what fluids were involved. If it were water, where did it go? The importance of providing an answer to this question is related to the fact that for the Earth, the presence of water was the key factor for the creation and evolution of life.
The most shocking pictures ever taken of another planet soon arrived. They involved the great Martian equatorial canyon. A canyon with a width of a hundred kilometers and a depth of 6 000 meters extending for more than 5 000 kilometers along the Martian equator: a structure that makes the Grand Canyon on the Earth look like a tiny cut. The axis of this depression probably formed as a result of the movements of the Martian crust. However, its borders are criss-crossed by many canals which, seen from the Earth, would certainly be recognized as river beds flowing towards the main artery. They have all the right features. If there are still any doubts about the origin of these structures, for others the analogy with Earth rivers is well beyond any doubt: winding courseways, well-defined banks, even river islands within the beds, with the characteristic droplet shape caused by the flow of the current. The presence of some freely flowing fluid in the past on the surface of Mars would thus seem to be beyond discussion. But we are on Mars, whose very thin atmosphere consists mainly of carbon dioxide and does not seem to be able to provide the abundant rainfall necessary to justify the presence of such massive structures. Therefore, scientists are still debating about what fluids were involved. If it were water, where did it go? The importance of providing an answer to this question is related to the fact that for the Earth, the presence of water was the key factor for the creation and evolution of life.
