Categorization of the Planetary Protection Policy for Planetary Ring Microparticles

Concepts of future sample return missions can include microparticles originated from planetary rings and gravitationally temporary captured objects around the planets of the Solar System. The current COSPAR Planetary Protection Policy has not determined baseline recommendations of forward and backward contamination categorizations for such planetary rings, apart from generic cases of interplanetary dust and fragments of known origins of asteroids and comets. Origins of planetary rings can vary from one to another. Most prominent and relatively long-lived rings around the giant gas planets may be generated through the formation and evolution processes of the planet's satellites with original constituents of the local planet-satellite system. Some other rings might have formed by dynamical interactions such as mutual collisions or/and intruder impacts of satellites and planetary tidal disruption of past satellites or gravitationally captured objects. In these cases, the ring particles should be fragments of the target bodies and impactors. Yet the other class of planetary rings may be formed by materials ejected from plumes of nearby satellites. It is thus important to scientifically evaluate both formation processes and subsequent alteration processes of respective planetary ring particles in order to propose their planetary protection categorization. For a case of backward contamination in sample return missions of such ring samples originated from sub-surface ocean plumes, sterilization processes by both natural and artificial means should be evaluated at the best of current scientific knowledges to see if they can be proposed as unrestricted Earth return samples. This study discusses all the above to set the latest scientific logics and to identify enabling technologies for categorization of the planetary protection policy for major types of planetary ring microparticles that may be subject to possible sample return missions in the near future.