Advancing Astrobiology Beyond Viking, Spirit and Opportunity

Abstract

Habitable environments must provide key chemical ingredients, biologically utilizable energy sources, and clement conditions where life can be active at least intermittently and thus ensure its survival. To find evidence of life we must explore atmospheres and crustal deposits that could have retained biosignatures (objects, substances or patterns that require biological origins). Then we must identify those biosignatures definitively. Viking, Spirit and Opportunity revealed that, although habitable environments probably do not occur at the Martian surface today, they might have existed at least intermittently in the past. Opportunity discovered that liquid water once stood on the surface. Spirit found that volcanic rocks had been altered by water in ways that could have provided chemical energy to sustain life. Recent missions revealed that the Martian crust has diverse compositions and has probably preserved an ancient record of aqueous activity and environmental changes. To enhance ongoing exploration of this crustal record for evidence of habitable environments and life, astrobiologists must participate in landing site selection and flight instrument development. Future landers should seek and examine geologic deposits (e.g., clays, evaporites, silica, carbonates, hydrothermal deposits, etc.) that might have formed in habitable environments and also could have preserved biosignatures. We must develop our concepts of biosignatures further to address potentially confusing nonbiological features that will inevitably arise.