LIFE ON MARS? |
Sean Henahan, Access Excellence
HOUSTON (August 7, 1996)
Analysis of a small meteorite that landed on Antarctica some 15
million years ago has sparked what may be the greatest
scientific discovery ever, possible evidence of life on Mars.
Graphic: False-color backscatter electron (BSE) image of
fractured surface of a chip from ALH84001 meteorite showing
distribution of the carbonate globules.
A team of researchers at NASA's Johnson Space Center have
identified organic compounds on the Martian meteorite, the first
ever such discovery. Details of the research will appear in the
August 16, 1996 issue of the journal Science. The embargo was
lifted after the news began to leak out. NASA held a press
conference today describing the findings.
"Scientists have made a startling discovery that points to the
possibility that a primitive form of microscopic life may have
existed on Mars more than three billion years ago," announced
NASA administrator Daniel Goldin.
The researchers looked for complex, carbon-based molecules and
other mineralogical and textural indications of past life within
the pore space and fractures of the meteorite known as Allan
Hills 84001 (ALH84001), one of only a dozen meteorites
identified as having come from Mars. ALH84001 is the oldest of
these, having crystallized from molten rock about 4.5 billion
years ago, early in the planet's evolution. It is the only
Martian meteorite to contain significant carbonate minerals.
The meteorite was flung across space following a major asteroid
impact some 15 million years ago. The scientists believe it
landed in an ice field in Antarctica about 13,000 years ago. The
meteorite was found in 1984 but only recently identified as
coming from Mars.
The researchers were amazed to discover the existence of
polycyclic aromatic hydrocarbons in fractures in the meteorite.
resulting primarily from impacts that occurred while the rock
was on Mars. The concentration and location of the PAH's led the
scientists to conclude that they are the remnants of bacterial
life forms. The scientists conducted exhaustive precautionary
procedures to confirm that the samples had not been contaminated
PAH's can form one of two ways: non-biologically, during early
star formation; or biologically, through the activity of
bacteria or other living organisms, or their degradation
(fossilization). On Earth, PAHs are abundant as fossil molecules
in ancient sedimentary rocks, coal and petroleum, the result of
chemical changes that occurred to the remains of dead marine
plankton and early plant life. They also occur during partial
combustion, such as when a candle burns or food is grilled.
The researchers examined the chemistry, mineralogy, and texture
of carbonates associated with PAH's in the Martian
meteorite. Under the transmission electron microscope, the
carbonate globules were seen to contain fine-grained
magnetite and iron-sulfide particles. From these and other
analyses, the team developed a list of observations about the
carbonates and PAH's that, taken individually, could be
explained by non-biological means. However, as they note in the
Science article, "when considered collectively...we conclude
that [these phenomena] are evidence for primitive life on early
Some of their key observations include:
The new discovery could not have happened at a better time for
NASA, which has been a subject of budget cuts recently. NASA
will be launching an unmanned spacecraft to Mars this Novemeber
called the Mars Global Surveyor. Another mission, the Mars
Pathfinder spacecraft will launch in December. NASA has
established an innovative program, "Live From Mars"
specifically designed for science teachers and their students.
- The highest concentrations of PAHs were found associated
with the carbonates.
- The carbonates formed within the rock fissures, about 3.6
billion years ago, and are younger than the rock itself.
- The magnetite and iron-sulfide particles inside the
carbonate globules are chemically, structurally and
morphologically similar to magnetosome particles produced by
bacteria on Earth.
- High-resolution scanning electron microscopy revealed on the
surface of the carbonates small (100 nanometers) ovoids and
elongated features. Similar textures have been found on the
surface of calcite concretions grown from Pleistocene
groundwater in southern Italy, which have been interpreted as
- Some earlier reports had suggested that the temperature at
which the ALH84001 carbonates formed was as high as 700�C --
much too hot for any kind of life. However, the isotopic
composition of the carbonates, and the new data on the
magnetite and iron-sulfide particles, imply a temperature range
of 0� to 80�C, cool enough for life.
- The magnetite -- a mineral which contains some ferric (Fe3+)
iron, perhaps indicating formation by oxidation (the
addition of oxygen) -- and iron sulfide -- a mineral that can be
formed by reduction (the loss of oxygen) -- were found in
close proximity in the Martian meteorite. On Earth, closely
associated mineralogical features involving both oxidation
and reduction are characteristic of biological activity.
"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. If this discovery
is confirmed it will surely be one of the most stunning insights
into our universe that science has ever uncovered. Its
implications are as far-reaching and awe-inspiring as can be
imagined,'' said President Clinton in a statement.
Clinton has directed Vice President Al Gore to convene a
bipartisan space summit' at the White House later this year to
discuss the future of America's space program including how to
pursue scientific questions raised by the Mars meteorite.
The new findings are certain to shake up the research community.
Some researchers are already suggesting it may be possible to
extrapolate the findings to outside of our solar system:
"It makes it very promising there may be life in other solar
systems. What it really does show is the formation of life on a
planet can take place rather easily,'' noted biochemist Stanley
Miller at the University of California at San Diego. Miller, who
specializes in the study of the origins of life is most well
known for his 'creation of life in the test tube' experiments.
Related information on the
Article: Search for Past Life on Mars: Possible Relic Biogenic
Activity in Martian Meteorite ALH84001, David S. McKay et al.
"Live From Mars"
NASA web site
Johnson Space Center
tion on Shergotty-Nakhla-Chassigny (SNC) Meteorites
Clues to The
Origins of Life