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which meant it experienced seasons just as Earth does - but of nearly double the
length owing to its much longer year. These observations led to the increase in
speculation that the darker albedo features were water and the brighter ones were
land. It was therefore natural to suppose that Mars may be inhabited by some form
of life.
Spectroscopic analysis of Mars' atmosphere began in earnest in 1894, when US
astronomer William Wallace Campbell showed that neither water nor oxygen was
present in the Martian atmosphere (Chambers
1999
). By 1909, better telescopes and
the best perihelic opposition of Mars since 1877 showed a Martian surface without
extended traces of life forms, as vegetation.
8.2
Modern Mars Astrobiology Research
Why Mars is so special?
Let us try to answer this simple but profound question.
First of all, a definition of astrobiology. Astrobiology is the study of the origin,
evolution, distribution, and future of life in the universe: extraterrestrial life and
life on Earth. This interdisciplinary field encompasses the search for habitable
environments in the solar system and habitable planets outside the solar system,
the search for evidence of prebiotic chemistry, laboratory and field research into the
origins and early evolution of life on Earth, and studies of the potential for life to
adapt to challenges on Earth and in outer space. Astrobiology addresses the question
of whether life exists beyond Earth and how humans can detect it if it does. The term
exobiology is similar but more specific - it covers the search for life beyond Earth
and the effects of extraterrestrial environments on living things.
Serious searches for evidence of life continue today via telescopic investigations
and landed missions. Modern scientific inquiry has emphasized the search for water,
chemical biosignatures in the soil and rocks at the planet's surface, and biomarker
gases in the atmosphere (Fig.
8.1
).
Mars is of particular interest for the study of the origins of life because of its
similarity to the early Earth. This is especially so since Mars has a cold climate and
lacks plate tectonics or continental drift, so it has remained almost unchanged since
the end of the Hesperian period. At least two-thirds of Mars' surface is more than
3.5 billion years (Gyrs) old, and Mars may thus hold the best record of the prebiotic
conditions leading to abiogenesis, even if life does not or has never existed there
(McKay and Stoker
1989
; Gaidos and Selsis
2007
). It remains an open question
whether life currently exists on Mars or has existed there in the past (Sagan
1980
).
On January 24, 2014, NASA reported that current studies on the planet Mars
by the Curiosity and Opportunity rovers will now be searching for evidence of
ancient life, including a biosphere based on autotrophic, chemotrophic, and/or
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