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Infecting Other Worlds

B. Randall Tufts, Richard Greenberg

Space Ethics

The basis for any evaluation must be a moral or philosophical principle. The one introduced by Sagan and Coleman could be applied to Europa with appropriate calculations. But their standard is self-serving, in that it does not address the well-being of life on another planet, except that it should survive long enough to satisfy human curiosity.

Figure 2. Just as astronomers took . . .Click to Enlarge Image

At the opposite extreme would be another principle—that preventing any interference with life on other planets should take absolute priority. We call this concept the "prime directive," borrowing this term from the television series Star Trek, which was contemporaneous with Sagan and Coleman's work and the COSPAR resolution. Actually, in Star Trek the prime directive usually applied only to protecting alien societies, and even then it was readily discarded as needed to advance the plot line. Yet the phrase seems appropriate here because it conveys a certain absolutism. The problem with this principle is that, if rigorously applied, it would likely bring exploration of some of the most interesting moons and planets to a halt.

Is there another moral principle that might provide a rational basis for developing a standard of planetary protection, one more objective than the principle of Sagan and Coleman and less constraining than the absolute isolationism of the prime directive? We recently proposed the following candidate principle, which is objective but not absolute. It is based on the idea that there is already a process of natural cross-contamination, something so far mostly quantified in the context of the terrestrial planets, which are thought to exchange chunks of crust from time to time after a large meteorite or comet hits and sends ejecta off into space at escape velocity. Living cells could conceivably survive such a journey: After all, many kinds of delicate organic molecules (including, perhaps, the very molecules that allowed life to develop here in the first place) are regularly carried to Earth within meteorites.

As long as the probability of people infecting other planets with terrestrial microbes is substantially smaller than the probability that such contamination happens naturally, exploration activities would, in our view, be doing no harm. We call this concept the natural contamination standard.

On one hand, the natural contamination standard for Europa may seem nearly as strict and confining as the prime directive, because the natural transport of viable organisms from Earth may be so difficult that it provides an impossibly stringent criterion. On the other hand, it may be equally difficult for organisms from southern California or Florida, where most planetary spacecraft are built and launched, to survive the voyage and proliferate in the cold, icy environments of Europa. One will not know until after careful scientific study.

We believe the natural contamination standard has considerable merit, but there may be other good candidates as well. The point is that before anyone can establish rules for the sterilization of planetary probes in a meaningful way, some fundamental principle, based on ethical and philosophical considerations, is needed.

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