Mars, Pluto,
and an array
of icy moons offer
possible places
where microbial
life might have
existed — or
might yet exist
today.
BY DAVID J. EICHER
THE SOLAR
STANDING UNDER A STARRY
sky and gazing up at its wonder, it’s easy
to believe that we’re alone in the cosmos.
The distances are vast, and, after all, we
know of only one planet in the universe
that hosts life — ours. But it’s possible
we may not be alone even in our own
solar system. Consider the facts.
What exactly is life, anyway?
Biologists define life as self-replicating
molecular systems that contain DNA
and RNA and use energy, reproduce,
and undergo Darwinian evolution.
There are other characteristics, but
those are the primary ones. And the
possibilities for life are actually pretty
intriguing. Spectroscopy tells us that
chemistry is uniform throughout the
cosmos. We know that basic organic
molecules are spread liberally through-
out the universe, even in the one andonly comet sample to be returned
to Earth.
It’s also a big universe out there. We
know of at least 10,000 billion billion
stars in the cosmos. And exoplanetary
systems near us in the Milky Way dem-
onstrate that most, if not all, stars should
also harbor planets. It’s exciting to think
of other sophisticated creatures we could
run into one day, or at least communi-
cate with from afar. That’s the basis of
the whole genre of science fiction. But
what about more commonplace life?
Biochemistry suggests that for every
place you might find sophisticated life
like us — hold the jokes — you would
probably witness many more places
hosting microbial life.
Some of those places might exist right
under our noses. Our most storied plan-
etary neighbor, Mars, has a long historyAre we alone in
Life in the
SOLAR
SYSTEM