One of the fundamental challenges facing the scientific community as we enter this new century of Mars research is to understand, in a rigorous manner, the biotic potential both past and present of this outermost terrestrial-like planet in our solar system. Urey: J.L. Bada ( ) Scripps Institution of Oceanography, La Jolla, CA 92093-0212, USA e-mail: [email protected] P. Ehrenfreund Leiden Institut...