Viking: the
Search for Life
In 1976 the Viking 1 and 2 landers undertook searches on the Martian
surface for the chemical evidence of present or past life on Mars. The
images shown below give a picture of one of the backup landers, and
two different views of the Martian surface as
photographed from Viking 1.
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Viking lander
(Ref)
and two views of the Martian surface from Viking 1
(Ref)
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In addition to photgraphing the surface, the Viking landers undertook a series
of experiments at two points on the surface to find evidence for life.
The Experiments
The 4
basic experiments that the Vikings carried out to search for evidence of life
were:
- Gas Metabolism: look for changes in the atmosphere induced by
metabolism in the Martian soil.
- Labeled Release: Look for release of radioactive carbon dioxide by
metabolism from organic material labeled by radioactive carbon.
- Pyrolytic Release: Search for radioactive compounds in soil
by heating soil exposed to radioactive carbon dioxide.
- Mass Spectrometer: Search directly in Martian soil
for organic compounds known to
be essential to Earth life.
These experiments were built around the hypothesis that if there were life on
Mars it would have a similar metabolism to life on Earth, and that it would
have a similar biochemistry based on the same organic compounds important to
life on Earth.
The Results
The results of these experiments were complex. The first three gave positive
results, but the complete absence of any organic compounds in the Martian soil
according to the mass spectrometer experiment suggests that the positive
results for the first three were not evidence for life, but rather evidence for
a complex inorganic chemistry in the Martian soil. Thus, the Viking verdict
was that there was no evidence for present or past life on Mars.
Renewed Interest in Martian Life
This issue has been given renewed impetus by the
recent claim
(see also
this and
this)
that a meteorite
found on the Earth was once part of Mars (because of detailed chemical
composition), and that there may be evidence in this rock for past organic
activity. However, this is a very open topic at the moment, since there
potentially are other explanations of the meteorite's content.
We will have to wait on further evidence to clarify this issue.
The Newest Martian Missions
-
Pathfinder which explored the Martian surface last year.
The image to the left is from Pathfinder on Mars.
-
Mars Global Surveyor: arrived in Martian orbit September 12, 1997.
Here is a summary of its trajectory from Earth to Mars.
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