Your body hosts roughly 100 trillion microbes, which makes every human a walking contamination risk for any pristine world. This episode explores planetary protection, the field dedicated to preventing forward contamination of other planets and back contamination of Earth. We trace the idea from a 1956 astronautical congress in Rome, before Sputnik, through the 1958 National Academy of Sciences push for sterilization, to Article IX of the 1967 Outer Space Treaty and how customary international law makes it binding even on non-signatories.

We then break down COSPAR's five mission categories, from the Sun and Mercury where anything goes, to Mars special regions and restricted sample returns from Mars, Europa, or Enceladus. You will hear how the Coleman-Sagan equation tries to keep contamination probability below one in 10,000, why critics cal ...