SYSTEM
of speculation about its potential for life.
Space missions put an end to science fic-
tion thoughts about martian creatures,
but ample evidence of past and recent
liquid water on the surface — and of
subsurface water and water ice — have
fueled ideas about microbial life on past
or present-day Mars.
Interestingly enough, research on the
icy bodies in the outer solar system has
led to a f lood of ideas about possible
microbial life out there. Before New
Horizons flew by Pluto in 2015, no one
really would have talked about the pos-
sible existence of microbes in slushy, icy
reservoirs beneath the frozen crust of
Pluto. But team members now talk about
that as a distinct possibility.
For a long time, dating back to the
Voyager missions, scientists have con-
templated icy moons of the solar systemas possible homes for microbes, past or
present. The poster child has been
Europa, one of the four Galilean moons
of Jupiter. Europa undergoes tidal heat-
ing from its large planet and has either a
subsurface liquid ocean or an icy, briny
layer of warm convecting ice underneath
its outer shell. Either one might make a
comfy place for organic chemistry to do
its magic and eventually produce some
self-replicating molecules.
And Europa isn’t the end game —
saturnian satellites also offer intriguing
prospects. Titan, the largest, has a dense
atmosphere and an exotic environment
consisting of methane and ethane lakes.
It is sometimes half-jokingly called the
“gasoline planet.” This might sound like
a strange place for microbes, but as
researchers have learned more about
microbial life on Earth, they have foundit to be hardier than ever dreamed of
before. If so-called extremophiles exist in
the most awful environments imaginable,
microbes could have evolved to thrive
in a methane-rich environment, too.
Saturn’s Enceladus also could offer
a rich environment for tiny life.
Cryovolcanoes on this icy moon shoot
watery geysers high above the moon’s
surface, and scientists have discovered
complex organic molecules in the moon’s
composition. Even farther out, Triton,
Neptune’s largest satellite, could also be
an icy abode for small living organisms.
This special report examines the pos-
sibilities for life existing elsewhere in
the solar system. It will take you on a
journey of the mind that, if you’re lucky,
will reshape slightly how you see life on
Earth, around you, every day of the year.
What do you think?WWW.ASTRONOMY.COM 23
?
JUPITER’S
MOON EUROPA
— which hosts an
ocean of liquid water
or slushy ice below its
hard, frozen surface —
is an enticing possible
abode for microbial
life. NASA/JPL-CALTECH/SETI
INSTITUTE