Geoscience Reference
In-Depth Information
planet from potentially life-threatening cosmic rays. The probe was able to calculate
the atmospheric pressure on the planet to be about 0.6 kPa (compared to Earth's
101.3 kPa), meaning that liquid water could not exist on the planet's surface. After
Mariner 4, the search for life on Mars changed to a search for bacteria-like living
organisms rather than for multicellular organisms, as the environment was clearly
too harsh for these.
8.3.9.3
Mariner 9
The images acquired by the Mariner 9 Mars orbiter, launched in 1971, revealed the
first direct evidence of past water in the form of dry riverbeds, canyons (including
the Valles Marineris, a system of canyons over about 4,020 km (2,500 mi) long),
evidence of water erosion and deposition, weather fronts, fogs, and more. The
findings from the Mariner 9 missions underpinned the later Viking program. The
enormous Valles Marineris canyon system is named after Mariner 9 in honor of its
achievements.
8.3.9.4
Viking Program
Viking Orbiters
Liquid water is necessary for known life and metabolism, so if water was present
on Mars, the chances of it having supported life may have been determinant. The
Viking orbiters found evidence of possible river valleys in many areas, erosion, and,
in the southern hemisphere, branched streams.
Viking Landers: Biological Experiments
The primary mission of the Viking landers by mid-1970s was to carry out experi-
ments designed to detect any moisture and microorganisms in Martian soil because
the favorable conditions for the evolution of multicellular organisms ceased some
4 billion years ago on Mars. The tests were formulated to look for microbial life
similar to that found on Earth. Of the four experiments, only the Labeled Release
(LR) experiment returned a positive result, showing increased
14
CO
2
production on
the first exposure of soil to water and nutrients. All scientists agree on two points
from the Viking missions: that radiolabeled
14
CO
2
evolved in the Labeled Release
experiment and that the GCMS detected no organic molecules. However, there are
vastly different interpretations of what those results imply.
By discovering many geological forms that are typically formed from large
amounts of water, the two Viking orbiters and the two landers caused a revolution
in our knowledge about water on Mars. Huge outflow channels were found in
many areas. They showed that floods of water broke through dams, carved deep
Search WWH ::
Custom Search