Abstract :
The surface of Europa may hold biochemical evidence of life in the ocean below. Plans for the analysis and return of samples containing organics from the surface of Europa are well developed; for example, the Ice Clipper Mission. Planetary protection issues must be considered in planning for a returned sample from Europa. Previous studies for sample return from Mars and the return of comet dust by the Stardust mission provide a basis for comparison for a Europa sample return mission. The extreme radiation environment on the surface of Europa would kill even the most radiation resistant microorganism present to depths of many tens of meters in the ice. The Ice Clipper mission would impact sample the upper 1.2 to 3.4 m of the ice depending on the surface hardness. At these depths the radiation dose is expected to be 500 and 40 rads/year, respectively. These dose rates would kill dormant cells in less than 36,000 and 450,000 years even for the most radiation resistant strains. It is therefore likely that a Europa sample return mission such as Ice Clipper can be treated using the Stardust mission as a model for planetary protection, that is, the returned material can be assumed to pose no biological risk.
