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 call its inputs guesswork, and the alternatives from Richard Greenberg’s natural contamination standard to the Space Studies Board’s decision trees. On the practical side we cover Class 100 clean rooms, the Viking landers baked at over 112 degrees Celsius for 30 hours, supercritical carbon dioxide snow, the polyextremophiles that clean rooms accidentally breed, trajectory biasing, the Mars Climate Orbiter unit mix-up, and the BSL-4 paradox of containing Martian samples while keeping Earth dust out.

• How a 1956 conference and the 1967 Outer Space Treaty turned a scientific suggestion into enforceable law
• COSPAR categories I through V and why Ganymede, Titan, and Ceres sit in provisional category II
• The Coleman-Sagan equation, the one in 10,000 target, and the debate over whether the math is an illusion of safety
• Why the Viking dry heat standard can’t be repeated on modern electronics and what replaces it
• The meteorite argument from Zubrin and others versus the National Research Council rebuttal, plus Christopher McKay’s biologically reversible exploration