The view was much improved with the 1976 Viking mission
(a pair of orbiters and landers). The images returned showed
an ancient surface covered with:
- craters
- a giant rift valley
(Valles Marineris)
- huge volcanic peaks (including
Olympus Mons,
with a height of
25 km above the mean surface making it the largest in the Solar System)
- winding valleys resembling dried up river beds: liquid water did
exist on the surface on Mars in the distant past.
The CO2 atmosphere was probably much thicker in the past; now most of the
CO2 is locked in carbonate rocks and sub-surface ices
(also water in permafrost).
The landers returned images of a
rock covered plain.
The Martian soils are
similar in composition to iron-rich clays (just like Georgia).
