By signing a contract today with Matra Marconi Space, Toulouse, the European Space Agency is giving Europe's space scientists a chance to find out. The contract is to build Mars Express which, when launched in June 2003, will carry a payload capable of conducting the most thorough search of the red planet yet for liquid water, which is essential for life as we know it. Features in the Martian landscape resembling valleys and dried-up river beds could only have been shaped by large quantities of flowing water, possibly mixed with other substances.
Some features even suggest catastrophic floods.
But sometime about 3.5 billion years ago, the Martian climate changed rapidly. The atmospheric pressure and temperature decreased very quickly. The water disappeared and Mars changed from a relatively warm, wet planet into a cold, dry one. One of Mars Express's tasks will be to assess these possibilities. If there is any liquid in the subsurface, then it's no more than a few kilometres down.