Who Are the Space Invaders? Planetary Protection and the Role of Biological Interactions between Extraterrestrial and Terrestrial Biospheres.

Exploring our solar system and returning pieces of it to Earth is a central part of the existential quest to search for life beyond our home planet. Understanding the biosafety and biocontamination implications of landing on a planetary body or in bringing pieces of our solar system back to our home planet are the two themes that are central to planetary protection, a discipline that is unique to spacefaring nations. The nature of planetary protection is twofold: (1) to ensure that we minimize our own terrestrial microbial footprint on other planets and moons (planetary bodies) in our solar system (forward contamination), and (2) to ensure that we minimize the potential impact of returning samples from another planet or moon to Earth (backward contamination). The discipline of planetary protection focuses on who is the biological "invader" and when does their arrival indicate an "invasion"? The degree to which there is potential for biological or organic interactions that result in biocontamination or changes in biosafety posture is the central topic of this work.