Geology Reference
In-Depth Information
(a)
Figure 4.1. Full-disk charts of
(a) the near side and (b) the far
side of theMoon. Darkmaria are
smooth, sparsely cratered
surfaces indicative of their
relatively younger age in
comparison with the heavily
cratered, bright highlands, or
terrae. In addition to selected
named features, landing sites
are shown (A, Apollo;
S, Surveyor;L,Luna;R,Ranger).
suggested that the craters were formed by gasses bubbling
up from the interior and bursting on the surface, like a pot
of boiling mush. Strange as this and some other ideas
might seem, the study of lunar craters served as the initial
steps in trying to understand the geology of extraterrestrial
surfaces. Eventually, two competing ideas emerged for
lunar craters, origins by impact and origins by volcanic
processes. These and other hypotheses would not be put to
rest until the Space Age.
When President Kennedy set the goal of sending
astronauts to the Moon and returning them safely to
Earth through the Apollo program, the newly formed
National Aeronautics and Space Administration formu-
lated an extensive set of exploration projects to learn
everything that would be needed in order to achieve
this national goal. Early on, it was recognized that we
knew very little about the characteristics of the Moon
that were critical for a successful landing. Debates raged
about the engineering properties of the surface, with
some scientists advocating that landers would sink out
of sight in a deep layer of
fluffy dust. To address these
and other concerns, a series of robotic spacecraft was
designed to collect much-needed engineering data. This
was also the time of the
“
space race
”
with the Soviet
Union. The Soviets also hoped to send men to the Moon
but, unlike the Apollo program, they did not formally
announce their goal, and it was only after the collapse of
the Soviet Union that their program was of
cially
revealed. Nonetheless, the Soviets had a highly success-
ful series of unmanned missions to the Moon, returning
data leading to many
“
rsts,
”
including views of the far
side of the Moon from the Luna 3 spacecraft. These and
later images showed that maria are mostly absent on the
far side (
Figs. 4.1(b)
and
4.4
).
NASA
'
s unmanned missions involved three projects,
Ranger, Surveyor, and Lunar Orbiter. Ranger spacecraft
were designed to crash on the surface but, on the way
down, to return a series of progressively higher-resolution
images to give close-up views of the surface. Although not
all of the missions were successful, Ranger images
