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1. Introduction; why quarantines? Mars
and Europa
Quarantine is from the Latin quadragina,
forty. The original definition is “…a period of forty days
during which an arriving vessel suspected of carrying contagious
disease is detained in port in strict isolation…” (Guralnik,
1970). Quarantines have been used throughout history to
protect against disease spread: smallpox, bubonic plague, or
rabies, and they are still applicable today.
Human history is filled with instances of
harmful plants, animals, and diseases being inadvertently or
deliberately introduced into a new locale with disastrous
results. The destructive effects of rabbits brought to
Australia or gypsy moths brought to North America are two
examples of good intentions gone awry. The deliberate use of
smallpox to exterminate native populations in the Americas is a
gruesome example of “germ warfare” (Diamond,
1997).
But what does this have to do with space
travel? A lot! While the Earth is the only known
place harboring life, there are locales in the Solar System that
have the potential for at least microbial life. The growing
appreciation of the hardiness of life on the Earth makes it
quite possible that Mars and Europa, in particular, may be home
to life. It is now known that microbial life on Earth can exist
at exist at extremes of temperature from above 1000 C
to far below zero. Life forms can live in highly acidic or
alkaline conditions and be resistant to very high pressures and
extreme radiation levels (Gross,
2001).
Life is very unlikely on Mercury, Venus,
comets, asteroids, the gas giants, and most of their frigid
moons. Titan and Enceladus are interesting because Titan has a
dense atmosphere and contains large amounts of organic compounds
but is extremely cold. Enceladus has cryovolcanism with
potential subsurface liquid water. The conditions existing on
Mars or in the subsurface ocean of the Jovian satellite Europa
could probably support many hardy terrestrial life forms (Rummel,
2001). Mars has considerable polar ice and subsurface ice,
probably once had liquid water on its surface, and even today
may have subsurface water that occasionally briefly flows onto
the surface (Rummel, 2001).
The composition of Europa and other Jovian and Saturnian
satellites is still being debated, but it is quite possible
there is a large subsurface ocean on Europa that occasionally
breaks through a thin surface crust of ice. It is an exciting
place to look for life (Lunine,
2004). Thus, it is not unreasonable to expect alien life
may exist in a limited number of places in the Solar System.
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