Geology Reference
In-Depth Information
(b)
Figure 4.1. (cont.)
showed a continuum of crater sizes right down to the
moment of impact. They also included views of features
that were correctly attributed to volcanism
(Fig. 4.5)
,add-
ing fuel to the debate regarding volcanism versus impact
cratering as agents of lunar surface evolution.
The Surveyor project involved
“
soft
”
landers (
Fig. 4.6
),
five of which were successful. These missions demonstra-
ted that the surface was suf
ciently solid to support land-
ers and provided engineering data for the lunar soils. They
also returned compositional information showing a pre-
dominance of iron-rich materials in mare regions, re
ect-
ing their basaltic lava composition, and revealed craters
only tens of centimeters across. Surveyor landers also
showed that the surface of the Moon is covered with
debris of a wide range of sizes from boulders to
ne
dust. The term regolith was borrowed from terrestrial
soil sciences and applied to this material, most of which
is generated by impact processes. At about the same time,
experiments using the impact facility at NASA
'
s Ames
Research Center (
Fig. 2.2
) were conducted to gain some
idea of the amount of fragmental material that can result
from impact. As shown in
Fig. 4.7
, even a pea-size object
can yield abundant rock fragments when impacting at
high speed.
The Lunar Orbiter (LO) series consisted of
ve space-
craft designed to return images for choosing Apollo land-
ing sites. The primary payload consisted of a medium-
resolution camera and a high-resolution camera that took
frames nested within the medium-resolution frames at ten
times higher resolution. The cameras used
film systems
that enabled on-board chemical processing, after which
the
film was scanned, and the data returned electronically
to Earth for reconstruction. LO frames can be identi
ed by
the
“
strips
”
of images, re
ecting the way in which the data
were reconstructed (
Fig. 2.20
).
The
first three LO spacecraft were placed in equatorial
orbits to photograph the surface at resolutions as high as
2m on the lunar near side. These orbits were chosen
because the Apollo landings would have to occur in the
near-side equatorial band to allow communication with
