On August 7, 1996, an historic press
conference was held at NASA Headquarters in Washington DC.
News that scientists had found evidence of life in a Mars meteorite
had leaked out, and NASA had to make an announcement. A few
minutes before, President Clinton made these remarks at the
White House before heading out on a trip to California:
"This is the
product of years of exploration and months of intensive
study by some of the world's most distinguished scientists.
Like all discoveries, this one will and should continue to
be reviewed, examined and scrutinized. It must be confirmed
by other scientists... I am determined that the American
space program will put its full intellectual power and
technological prowess behind the search for further evidence
of life on Mars."
At the press conference, several
scientists from NASA and Stanford University announced their
findings -- they confirmed that they had found evidence of
ancient, fossilized, microscopic life from a Martian
meteorite, known as ALH84001. The meteorite was catapulted
away from Mars fifteen million years ago when a huge comet or
asteroid impacted the surface. The meteorite travelled through
space for millions of years and then encountered the Earth. It
entered Earth's atmosphere about thirteen thousand years ago
and landed at Antarctica. The meteorite lay there until 1984,
when a team from the NASA Johnson Space Centre found it while
exploring the Allan Hills ice field, and brought it back to
Houston. It was initially classified as a lunar meteorite, but
in 1993 was correctly identified as from Mars. It is one of
only twelve "SNC" meteorites, which match the unique
chemical signature of Mars.
The scientists talked their reasoning
for the discovery -- they had four independent lines of
evidence which, when taken together as a whole, ancient life
on Mars is the logical conclusion.
Do these orange carbonate globs contain the remains
of millions of ancient Martian life forms?
(Courtesy Science Magazine)
The carbonate patterns form a unique signature of life, and
the density and composition of the carbonate patterns is
consistent with how terrestrial bacteria operate. Carbonate
by itself, however, is abundant in non-living materials.
aromatic hydrocarbons (PAHs)
Organic compounds usually created by bacteria were present
in the meteorite. There has been much controversy about
whether or not the PAHs are contaminants from the Antarctic
environment, or are present from Mars.
These globules are created by bacteria on Earth as well as
some chemical processes. However, the distinctive tear-shape
in the Martian evidence is only created by bacteria. Some
scientists are still not convinced.
The most dramatic evidence of all, pictures were shown at
the press conference of worm-like structures present in the
meteorite. While they are much smaller than terrestrial
bacteria, they look very similar, but could also just be
mineral structures. More pictures have been created since
then. The initial scepticism about them has partially been
silenced by recent discoveries of similar terrestrial
fossils of similar (nanobacterial) scale.
All of these features occur within a few
hundred-thousandths of an inch together. The most logical
conclusion is that it's ancient bacteria (life!). Immediately,
other scientists disputed the findings, and a grand debate
continues to this day. Neither side has convinced the other
and there is abundant evidence both for and against Mars life
in the meteorite.
Are these worm-like structures fossilised Martian
bacteria? (Courtesy NASA/JSC)
While the life they talked about was only microscopic, it has
several implications for us macroscopic creatures. If life on
Mars is ever proven to to exist (or have existed at some point
in time), it would mean that the creation of life is not
something that happens because of freak chance or divine
influence, but is in fact a probable occurrence given the
right conditions. Even further, if all that life requires is
an aqueous solution like liquid water to grow and thrive
(which is the current theory), then the universe is literally
teeming with life. The suspected liquid water oceans on some
of Jupiter's moons (Europa and Callisto) could be filled with
life, and life could still be present underneath the Martian
surface, where liquid water and thermal energy are still
Experiments: More Evidence for Life?
Apparent evidence for life on Mars has been found before, and
it's worth a second look now. The Viking Landers, which
were sent to Mars in the 1970s, carried several experiments
designed to detect organic materials and organisms on the
Martian surface. However, the experiments were designed with
limited knowledge of Mars because at that point, no spacecraft
had ever successfully landed on the Red Planet. When the
Viking Landers arrived on Mars, the results were ambiguous.
While one experiment detected no organic compounds in the
soil, another -- the Labelled Release experiment (LR) -- found
positive results. The LR was designed to drop a nutrient
solution into a soil sample from Mars, and then measure the
changes in the gaseous sample container to determine if the
changes were organically induced (if bacteria were multiplying
because of the nutrients they'd been given). When the
experiment was conducted on both Viking Landers, it gave
positive results almost immediately.
Most scientists on the Viking mission
came to the conclusion that the positive results were
attributed to the discovery of oxides in the soil, and that a
chemical reaction occurred when the nutrient solution was
mixed with the oxides. However, the LR's designer and
principal investigator, Dr. Gilbert Levin, was convinced that
his experiment found life. He remains convinced to this day
and has recently published a paper with additional findings.
However, his conclusions have been rejected by mainstream
scientists (which is not surprising considering their
Levin also says that the experiment
which did not find organic materials in the soil were not
sensitive enough to detect it in small amounts. This has been
confirmed by NASA as possible, since ALH84001 clearly contains
organic materials (which may not necessarily have been created
by living organisms). The experiment in question was tested in
Antarctica and found negative results, which is definitely
wrong because there are organic materials there!
Search for Life Question
The debate continues. Future missions to Mars will address the
question of Life on Mars. In 2005, a Mars Sample Return
mission will attempt to bring back likely candidate samples of
minerals in which these kind of fossils would occur. If
successful, and similar evidence is found, the critics will be
silenced. However, it's a long-shot that a suitable sample can
be found by a remote-controlled rover. The best thing would be
to have a trained field geologist with a rock hammer. A human
explorer would offer on-site experience, better mobility
(presumably he'd have his own rover to drive around in), and a
much better chance of finding evidence for life. So, in the
end, the best way to settle the debate is to send people to
Mars. In the opinion of the Mars Society and many experts,
this question alone is enough to justify a Humans
to Mars program.