Space Physics, Mars, and Life

摘要

The ultimate challenge of astrobiology to-day is to seek and find recognizable signs of life on solar system planets and moons, whose surface environments are generally hostile to the survival of life and its biosignatures. The controversial case in point is the Mars Viking Lander experience, which "produced ambiguous results that failed to establish the presence of life, identified unusual oxidative soil chemistry not anticipated during the experiment design, and left a lingering controversy over some of the results" (NRC-COEL, 2002). Future missions to icy worlds such as Europa, Enceladus, and Titan, all of which show the potential for either liquid water or prebiotic chemical precursors, will inescapably need to contend with the radiation products of space physics environment. Dusty Mars and icy Europa have in common the presence of abundant surface oxidants respectively produced, directly or indirectly, by irradiation. The dominant forms of life on Earth either produce or utilize molecular oxygen, and astronomical investigations for life on extrasolar planets will search for atmospheric oxygen in the form of ozone, another space irradiation product. Europa and Mars might conceivably have subsurface ecologies supported by naturally produced oxygen in different forms from the surface irradiation environment. The same radiation-induced chemistry produces oxygen radicals and peroxides that destroy exposed organic materials, so the oxidants are both potential blessings and curses for any life and associated signs of life in these environments.