The two Viking probes were launched from Earth in 1975 and
entered Mars orbit in 1975. Each Viking consisted of two space craft, an
orbiter and a lander. Each orbiter had a pair of cameras and instruments for
mapping surface temperature and atmospheric humidity. Each lander included a
weather station, a seismometer for detecting "marsquakes,"
instruments for analyzing soil, and a stereo TV camera.
The Viking 1 lander touched down on the Chryse Planitia in
the northern lowlands on July 20th,
1976, exactly seven years after the first Apollo moon landing. Its
video cameras took the first pictures of the Martian surface. Its landing site
was a desolate plain of dark, rounded rocks, probably volcanic, and red dust
under a pink sky. Though Viking 1 landed at about the equivalent latitude of
the Sahara Desert, temperatures ranged from a high of -10°C (14°F), and to a
numbing low of -90°C (-130°F). Winds were light, at about thirty kilometers an
hour.
The Viking 2 lander touched down on Utopia Planitia, closer
to the Martian North Pole about two months later. The Viking 2 landing site is
rockier than that of Viking 1; it is flat with a few low, crater hills in the
distance. Its winter night temperatures dropped to -120°C (-184°F). In winter,
a thin layer of water frost was present for several months.
The Viking landers discovered no life, even microbial. The
robot arms of the landers scooped up some soil for analysis with instruments
designed to detect signs of life. The instruments cooked the soil, soaked it,
and fed it nutrient broth. Although the soil contained no organic material, a
few experiments seemed to indicate signs of living organisms. However, after
years of debate, most scientists now agree that the life signs came from
unusual minerals in the soil, and that Mars' surface, at least around the two
Viking landing sites, is lifeless.
In the meantime, the two Viking orbiters mapped the Martian
surface and analyzed its surface temperature and atmosphere. The orbiters’ instruments discovered an
abundance of water in the Martian atmosphere. Over 5200 images were taken of
the Martian surface, mapping the red planet in greater detail than ever before.
Insights into Mars’ volcanoes, water, and ancient history are being studied to
this day.