The dispatch of unmanned spacecraft to the planets and their moons is, however, only the first step in our exploration of the solar system. Just as astronauts followed satellites into Earth orbit and, later, to the Moon, so will they one day venture towards the planets. Indeed, the Moon has often been mentioned as an ideal environment for an astronomical observatory because of its limited atmosphere, surface stability, lack of erosion or wind loading, and the availability of natural radiation shielding.41

The problem, as our limited experience of manned lunar exploration has shown, is that explorers take their equipment, their infrastructure, and their habits with them. And if no binding, anticontamination or nonpollution agreements are in place, the explorers could leave an indelible and irreversible imprint on the environment they are attempting to study.

The history of exploration of terrestrial wilderness areas provides a useful analogy to this new phase of exploration. In the early days of Himalayan exploration, for example, Earth's highest mountain was considered a challenge for human endurance, an obstacle to conquer, and even as a result of failed attempts a killer. Attempting to reach the summit of Mount Everest was considered the laudable occupation of true heroes.

The fact that the slopes of the mountain have been littered with empty oxygen cylinders and other detritus as a result of the many attempts was accepted, for a long time, as a necessary prerequisite for conquest. It was also the case that, although ordinary hill walkers were encouraged...