The protection of the planetary environments, which include the planets' moons, is generally led by the desires of planetary scientists to maintain the original "purity" of the environments they wish to investigate. The nub of planetary protection is encapsulated in the phrase "forward contamination," which can be defined as "the contamination of a planetary body other than the Earth, which may occur as a result of landing a spacecraft on that body,"15 or indeed allowing it to crash there. The contamination of the terrestrial environment, which may occur as a result of returning samples from another planetary body, is known as back contamination.

The history of exploration on Earth can quote several examples of explorers taking diseases to isolated societies that had no immunity and wiping out their civilizations. Some worry that a similar thing could happen to indigenous life-forms, however simple, as a result of our exploration of the planetary bodies. Even more disturbing is the possibility that a sample returned from, say, Mars or Europa could contaminate the Earth. At present, this reads like many a science-fiction tale, but history has also shown that space exploration has a habit of turning science fiction into fact.

Surprising though it might seem, given the relative insensitivity of early space explorers towards the space environment, the first international effort at dealing with extraterrestrial contamination came as early as 1956, when the International Astronautical Federation (IAF) attempted to coordinate efforts at its seventh Congress in Rome.

Following the launch of...