might be a Scientist if you are able to hold in your mind two
opposing ideas at the same time. Then again, if you can
do that, you can excel at any number of human endeavors.
Science above all requires this kind of flexibility of
thinking, because there isn't always sufficient
evidence to completely cut off one
of two opposing possibilities. In the past we've
discussed scientific questions about which there is
substantial, decisive evidence. This time, we discover
something new about how Science works while we're still in the
process of finding things out.
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There is not now and never has been any life on Mars.
There may have been or may still be microbial life on
Mars. How can I say both? Because that is what the
evidence says. Most scientific facts begin this way -
with two or more distinct possibilities that are both
completely plausible, and often contradictory.
When we entered Space in the 60's, we soon figured out that
Mars was not inhabited by little green men bent on conquering
and enslaving Earth. The Viking mission in the mid 70's
and many subsequent missions to Mars gave us huge amounts of
data to digest. A clear picture of a sterile, lifeless
Mars emerged from that mountain of information.
But then someone picked up a rock on Earth and studied
it. It was not an Earth rock, but careful analysis
revealed, improbable as it was, that it was actually a
piece of Mars. Sometimes when a meteor hits a planet,
pieces of the planet get blasted way out into space.
That happens to Mars as well, and occasionally some of those
pieces of Mars land on Earth.
The unusual thing about this particular piece of Mars was
that it contained microscopic shapes in the rock that looked
like tiny spheres. Tiny spheres can occur any number of
ways, but the most provocative possibility was that they might
be fossilized micro-organisms - once living cells which atom
by atom have been replaced by lifeless minerals that preserve
the original shape.
The discovery of this evidence was widely publicized and
criticized. It was impossible to rule out the many ways
that these shapes might have come to
exist independently of "life" on Mars.
More recently, the Spirit
and Opportunity rovers discovered rocks on Mars
containing Calcium Carbonate or Limestone. This
has re-opened the question of life on Mars and is one
more piece of evidence in favour of it. Living organisms
on Earth have in the past (1 - 3 billion years ago) been
responsible for producing this mineral. It is still
happening today at two locations in Western Australia.
in the Peel region and the Stromatolites
near Shark Bay are two examples of "Living Rocks" in which
microbes suck up carbon dioxide and burp out oxygen while
forming an ever- growing fortress of limestone around
them. That is, we hope they burp, and not . .
Although Life is not the only way that limestone
could have been formed on Mars, the possibility can't be so
easily dismissed either. For the moment, both
possibilities - that life never existed and that life did or
still does exist on Mars - seem roughly equally "true," or in other words, "that for which evidence exists."
Do other worlds in our solar system hold out the
possibility of microbial or even animal life? Only
one. Europa, the fourth largest moon of Jupiter (the
smallest Galilean moon, just visible with a backyard
telescope), is covered by a layer of ice 60 miles thick, under which an ocean of
liquid water lies hidden. Planning is underway for a
future mission to tunnel down to that ocean and find out once
and for all if it contains living creatures.
I invite you to read more about Water
and the Search for Life on Mars. Also, a new book explores the
intriguing possibilities that are hidden under the ice on
Europa: The Search for Life on Jupiter's Ocean Moon is another that I recommend to you
personally. I hope you enjoy reading these!