Most of the oxygen in the Martian atmosphere is present as carbon dioxide (), the main atmospheric component. Molecular oxygen (O2) only exists in trace amounts. Large amounts of oxygen can be also found in metal oxides on the Martian surface, and in the soil, in the form of per-nitrates. An analysis of soil samples taken by the Phoenix lander indicated the presence of perchlorate, which has been used to liberate oxygen in chemical oxygen generators. Electrolysis could be employed to separate water on Mars into oxygen and hydrogen if sufficient liquid water and electricity were available. However, if vented into the atmosphere it would escape into space.