Planetary Protection Starts Before a Spacecraft Launches

The first sample may come from Earth

A mission searching another world for signs of life faces an awkward possibility: some of the material it detects could have travelled there on the mission itself. That does not make exploration pointless. It means that a convincing discovery requires information about the spacecraft, its preparation and its contact with the environment, as well as information about the sample.

NASA's planetary protection office describes control of forward contamination as protecting other worlds and the integrity of life-related investigations. It also addresses backward contamination when material is returned to Earth. These are related responsibilities, but they involve different directions of movement. For a reader, separating them prevents a common misunderstanding: rules for preparing a departing spacecraft are not identical to rules for handling a returned sample. Both belong to the design of the investigation.