The foremost question for Martian exploration is where to find environments favorable for pre‐biotic chemistry or the growth of primitive life. Hydrothermal systems are the most sought after targets because terrestrial life probably originated in such systems, while lake deposits provide another good environment for preservation of clues to astrobiological processes. Craters can be filled with surface water from outflow channels and valley networks to form lakes with accompanying sedimentation. The great depth of impact craters, up to several kilometers relative to the surrounding terrain, can also result in a source of water for lakes and hydrothermal systems from local aquifers. Therefore, large craters may represent giant Petri dishes culturing preexisting life on Mars and promoting biogeochemical processes. Landing sites must be identified in craters where processes, such as erosion, or excavation by later cratering events has provided access to the buried lake sediments and impact melt deposits.

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