Devout
exobiologists fervently believe that life may exist, or could have existed, on
four other worlds in our solar system. The
candidates are Mars, Europa, (a moon of Jupiter), Titan, (a moon of Saturn),
and now Enceladus. Like Titan, Enceladus
is a small moon that orbits the planet Saturn.
All four worlds to varying degrees possess the attributes that could support
life as we know it: liquid water,
carbon, nitrogen, and a source of energy.
Mars
has failed to show any signs of even microbial life, past or present, despite
its near Biblical standing as a kind of Promised Land for extraterrestrial
organisms. It is also lacking in
nitrogen, important in the formation of amino acids and proteins.
Enceladus
is in the news this week. Analysis of
the data sent back by NASA’s Cassini spacecraft suggest the presence of an
underground body of water the size of Lake Superior. The small sea is perhaps 20 to 25 miles
beneath the moon’s icy face. Cassini
flew by Enceladus three times between 2010 and 2012, snapping pictures of the frozen
surface; changes in its speed and trajectory were studied in order to develop a
map of the moon’s gravitational field.
Geysers of ice crystals had also been observed at the moon’s south pole.
Just
over 300 miles wide, Enceladus is a shiny, smooth faced world that reflects
nearly 100% of the sunlight that strikes it.
It is a very cold place, being negative 330 degrees Fahrenheit on the surface. Its terrain is broken up by fissures, hilly
regions, and plains, but relatively few craters, which suggests that the moon
has been geologically active in the recent past. Heat energy in its core is generated by tidal
forces—its orbit is affected by gravitational forces from Saturn and
neighboring moons. It is thought to have
a liquid interior as well as a slight atmosphere containing water vapor.
Evidence
for an underground sea has not been directly observed but inferred from analysis of the satellite’s gravitational field,
which is weaker at the south pole.
Scientists speculate that liquid water has the requisite density to
account for what should otherwise be a weaker gravitational force at the pole. Thus, there must be an enormous underground
body of liquid water near the south pole.
Several scientists are proposing a mission to Enceladus. If samples of ice crystals from the geyser
sites can be brought back to earth—with suitable precautions—they can be
examined for extraterrestrial microbes.
Exobiologists
have reasoned metaphorically that because life can exist in such extreme Earth
environments as deep undersea volcanic vents and the Antarctic wastes, it must
also exist in similar locations on other worlds. Elaborate mathematic formulas have been used
to infer the presence of optimal conditions for extraterrestrial life, when
direct observation is not possible.
These
speculative methods have been used to locate over a thousand “exoplanets”, circling
nearly as many stars. Of these planetary
systems, nearly 200 have multiple planets.
Out of all these worlds, at least nine exoplanets and possibly 30
planetary moons lie in the habitable orbital zone of a star—defined as at a
sufficient distance from the star to allow liquid water to exist. It seems that every month or two a few more
exoplanets are discovered using this methodology; typically these are “gas
giants” like our own Jupiter and Saturn.
(See also How Many Extraterrestrials Are There? )
Besides
watching, we have also been listening for
signs of life in the cosmos. SETI has
turned its enormous ear to the heavens since 1961. Alas, no identifiable signal has come to
Earth—it has been very quiet out there.
My hunch is that it probably will remain so.
Strictly
speaking, none of this is really science, since it involves more inference than
actual evidence. The reporting about
Enceladus is another example of reason in the service of a persevering faith. It verges on science fiction—entertaining,
intriguing, perhaps even good public relations—but not verifiable. Based on the evidence so far, collected over
decades, it would seem that the only life that exists in the universe is on Earth, where it was created. Yet the
stars and planets out there were also created—and for us.
Despite
my criticism of efforts to find extraterrestrial life, your humble blogger
supports aggressive space exploration and colonization of the moon and nearby
planets. This is not so much to aid in
the search for life on other planets, but for business. Imagine the
natural resource wealth available to us in the asteroid ring between Mars and
Jupiter! Colonies could serve as mining
and refining stations to enrich our planet’s store of valuable metals, and our
environment can improve as energy production and manufacturing are moved off
our home and onto nearby locations in space.
Good old business will take us beyond our home world, and help bring
life to an empty cosmos.
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