The quest for habitats in the outer Solar System and how to protect exotic pristine environments

The search for life within our Solar System and beyond has been a key motivation for space exploration since its inception. These efforts have focused on specific celestial bodies located within the "habitable zone". Mars has long been a primary target for exploration, but the large moons of the gas giants Jupiter and Saturn have also emerged as fascinating astrobiological candidates, offering promising conditions for habitability and the potential for life to emerge and persist. To ensure safe and sustainable exploration of these bodies, the 114 countries that signed the Outer Space Treaty in 1967 assigned the Committee on Space Research (COSPAR) the task of creating planetary protection guidelines. These guidelines are designed to align with the Treaty and prevent the harmful effects of both forward and backward contamination. While the planetary protection policy established by the COSPAR Panel on Planetary Protection (PPP) is not legally binding, it is internationally recognized and accompanied by implementation guidelines for all stakeholders. The PPP focuses on the biological exchange that occurs during solar system exploration, including the chemical evolution and the origin and development of life forms. It examines the potential impacts of contamination from Earth-based organisms on the environments of planets other than Earth and natural satellites, and also considers the risk of contaminating Earth with materials returned from space that may carry extraterrestrial life (cosparhq.cnes.fr/scienti_c-structure/panels/panel-on-planetary-protection-ppp/). The COSPAR Policy is grounded in the latest scientific understanding and adheres to the principle that COSPAR's planetary protection guidelines should facilitate, not hinder, Solar System exploration by being regularly reviewed and updated in line with new scientific discoveries and the evolving demands of space exploration. In this paper, we review our current knowledge of the possible habitats in the outer Solar System and their current and future safe and sustainable exploration (for example, with missions like Juice, Europa Clipper and Dragonfly) to secure access to unique and primordial information on the origin and evolution of life on our own planet. • Planetary protection enables scientific space exploration and protects the Earth. • A Planetary Protection (PP) Policy has been developed by the COSPAR Panel on PP. • It is an agreed international standard with guidelines for compliance with the OST. • It is based on the most recent scientific knowledge. • The Policy allows to safely explore possible habitable worlds in the solar system.