Geology Reference
In-Depth Information
Figure 1.7. The
rst
successful landing on
Mars was the Viking 1
lander, shown in this
diagram with its
principal components.
planetary objects, such as their size and density, and the
presence or absence of atmospheres.
The first exploratory missions are usually
Spacecraft in polar or near-polar orbits can obtain remote
sensing data for the entire planet, enabling assessments of
the surface complexity, collection of geophysical data,
and measurements of topography. Thus, one of the pri-
mary advantages of orbiters is the collection of global
data.
Once a planet has been surveyed from orbit, the mis-
sions that follow can include landed spacecraft. Landers
enable
“
ground-truthing
”
of the remote sensing data
obtained from orbit. Such data include in situ measure-
ments of surface chemistry and mineralogy, determina-
tions of the physical properties of the surface enviroment,
and geophysical measurements, including seismometry.
Landed missions are signi
cantly enhanced by surface
mobility as afforded by robotic systems, such as the
Mars Exploration Rovers (
Fig. 1.10
). The advantage of
in
which spacecraft zoom past planetary objects and, over a
period of only hours or a few days, collect data. Although
limited, these data provide the
first glimpses of the object
up-close and are far better than those obtained from Earth-
based telescopes. For example, in 1979 and the 1980s the
spectacular Voyager 1 and 2 spacecraft (
Fig. 1.9
) revealed
the complexities of the moons of Jupiter, Saturn, Uranus,
and Neptune during brief
“
ybys,
”
flybys of
those planetary
systems.
Next in exploration comes the use of orbiting space-
craft. Remaining in orbit for days, months, or even years,
orbiters provide the opportunity for more complete map-
ping and observations of potential seasonal changes.
