Though NASA has no confirmed plans for a Europa orbiter mission, NASA and the international space science community are exploring possibilities for a mission that will meet the science challenges posed by this unique Jovian moon, as recommended by the National Research Council’s Decadal Strategy for Solar System Exploration. This mission would be intended to build on the Galileo mission’s observations of Europa, Ganymede, and Callisto, by conducting more in-depth orbital investigations of Europa, which may have a subsurface liquid ocean and significant energy sources. Planetary protection considerations are thus a key component of planning for a Europa orbiter, and possibly for a lander that may accompany the mission. Planetary protection requirements for this mission will focus on ensuring that the spacecraft will not inadvertently crash into one of Jupiter’s moons and thereby risk melting ice and possibly contaminating liquid water. Planetary protection standards recommended by the National Research Council’s Space Studies Board for missions to Europa (Preventing the Forward Contamination of Europa) would limit the probability of contaminating liquid water on Europa with a viable terrestrial organism to less than 10-4 per mission.
If properly employed, current NASA methods of spacecraft cleaning and sterilization, as well as the natural influence of Europa’s harsh radiation environment, appear to be adequate to prepare a Europa orbiting spacecraft. The mission as currently conceived appears to require a NASA Category III planetary protection classification, with a lander being a Category IV addition. Nonetheless, any new knowledge about Europa or the boundary conditions for microbial life will be taken into consideration in finalizing planetary protection requirements for the mission. Specific planetary protection measures that are likely to be imposed on the mission include: reduction of spacecraft biological contamination, focused on cleaning the spacecraft from the inside out, constraints in spacecraft operating procedures such as adoption of fail-safe long-term orbits, spacecraft organic inventory and restrictions, documentation of spacecraft trajectories, and spacecraft material archiving.