SME:
John Connolly and Chuck Lloyd
Mars has always made us wonder.
Why is it red? Was there ever water on its surface? Will
we find life there? Answers to these questions and others
will come from studying and traveling to Mars.
Mars is called
the “red planet” for a very good reason -- its surface looks
red to our eyes. The soil is rusty, containing iron, the
same chemical as rusty metal. Long ago, parts of Mars may
have been covered in blue – blue oceans. Robot
landers and
other space probes show evidence that parts of Mars were
once covered with liquid water.
Since 1997, NASA’s Mars Global Surveyor spacecraft has taken
pictures of the Martian surface. Parts of its surface look
like a flash flood has washed over the land, similar to flooding
seen in the western United States. Some pictures from its
high resolution cameras seem to show signs of past major
flooding along Mars’s equator.
In 2004, NASA landed two robot rovers called Spirit and
Opportunity on Mars. These rovers investigated rocks and
soil and took pictures of features that seem to prove Mars
was very wet in the past.
Water already has been found on Mars in the form of ice
in the polar ice caps. The Martian ice cap in the north is
about 4 kilometers (2.5 miles) thick. Another place on Mars
that probably contains a lot of frozen water is in the permafrost
that is buried just below the surface. The Martian permafrost
may be several kilometers thick all over the globe and
may be as much as half ice.
Based on what we have observed so far, Mars today is a frozen
desert. It's too cold for liquid water to exist on its surface
and too cold to rain. The planet's atmosphere is also too
thin to permit any significant amount of snowfall. You cannot
breathe on Mars because its atmosphere contains so little
oxygen.
Finding evidence that helps prove Mars had liquid
water in the past supports the ideas and beliefs that life
could have existed on Mars. Many questions about the history
of water on Mars are likely to remain unanswered until samples
are returned from the red planet for examination on Earth.
In 1976, NASA landed two Viking spacecraft on Mars. Viking
tested the soil to see whether any life was present. Using
a small scoop, Viking dug into the Martian soil. It picked
up small samples, dropped them into a bin, and looked for
signs of life.
What kind of life did the scientists expect
to see? They based their experiments on the idea that life
on Mars would be very simple, something like the bacteria
found on Earth. They looked to see if anything in the Martian
soil seemed to be “eating” organic
materials or giving off
gases like carbon dioxide.
What did the scientists discover? There seemed to be some
interesting chemical activity in the soil but no clear proof
of any living things.
We can find more clues about Mars by
studying meteorites.
We have discovered about a dozen meteorites on Earth that are thought to be from Mars. All are igneous
rocks that formed from molten magma. They have a similar
form of oxygen and higher concentrations of iron and water
than other meteorites. Gas bubbles trapped in one meteorite
match the current Martian atmosphere as measured by the Viking
Landers.
And, they contain some evidence that points to possible
life. High-resolution scanning electron microscopes show
the presence of tiny “ovoids” that may be the fossil remains
of very tiny bacteria. If so, they are 100 times smaller
than any bacteria microfossils found on Earth. Perhaps there
was once simple bacterial life on Mars.
Mars is almost certain
to have been warmer and wetter in its distant past, so the
existence of simple life has been a tantalizing possibility
for some time. The real search may be just beginning.
Future
NASA missions will land on Mars, collect rock and soil samples,
and return them to Earth. We hope to learn much more about
the red planet and, perhaps one day, send people there to
explore firsthand |
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