MACROSCOPE
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.
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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