Water and Life On Earth, life requires water, therefore our search for life beyond the Earth is a search for water. For this reason we target Europa, a moon of Jupiter that may have a liquid ocean beneath a thick icy crust, and also Mars where huge erosional channels suggest the flow of fluids across the surface in the geological past.
Many scientists believe that rivers and lakes existed in the past on Mars, and perhaps even oceans.
However, this search on Mars may be ill-founded. Despite intense research, the evidence for water on Mars is scarce. Canals Over a century ago astronomers peered at the blurred image of Mars, and thought they saw faint lines marked across its surface. There is also water on Mars, or at least H2O - but this is almost exclusively in the solid form in the permanent Northern polecap, and perhaps also in polar permafrost. Much of the surface of Mars is revealed by orbiter and flyby images to be heavily cratered, rather like the Moon or Mercury.