Geology Reference
In-Depth Information
CHAPTER 9
The Saturn system
9.1 Introduction
to make a close pass by Saturn
'
s giant moon, Titan,
Voyager 1 also took high-resolution pictures of Mimas,
Dione, and Rhea. The path of the Voyager 2 spacecraft
was designed so that it would
y past Uranus and Neptune
with a trajectory that nicely complemented that of Voyager 1
and provided close views of Saturn
'
s moons Iapetus,
Hyperion, Enceladus, and Tethys. In addition to spacecraft
observations, the Hubble Space Telescope has provided
critical new information, especially on Saturn
Saturn is an enormous planet, second in diameter only to
Jupiter. From the discovery of rings around Saturn nearly
400 years ago until the last three decades when rings were
found around the other giant planets, Saturn was thought
to be unique in the Solar System. Saturn has at least 62
satellites, including Titan, which has global clouds and an
atmosphere denser than that of Earth, and the moon
Enceladus with its actively spewing geysers. Titan is the
only outer planet moon on which a spacecraft has landed.
Consequently, the Saturn system holds a special place in
our view of the Solar System.
'
s clouds.
Huygens mission is a joint project that
involves the NASA Cassini orbiter and the ESA Huygens
probe of Titan. This mission is a
“
“flagship-class”
”
project
and is the largest and most complex planetary spacecraft
launched to the outer Solar System. Launched in 1997, it
followed a trajectory similar to that of the Galileo Jupiter
spacecraft by looping around the Sun to gain suf
cient
momentum to
“
sling-shot
”
into the outer Solar System.
This involved two
flybys of Venus (in 1998 and 1999)
and one past Earth (later in 1999), during which some
instruments were calibrated using Earth
The Cassini
-
9.2 Exploration
When Galileo viewed Saturn through his telescope for the
first time in 1610, he apparently thought he was seeing three
separate objects, but later observations led to his publishing
a sketch in 1616 that clearly showed Saturn and its ring
system. Rapid improvements in telescopes and their appli-
cation to planetary observations resulted in more detailed
descriptions of Saturn and prompted wide speculation on
the origin and characteristics of its system of rings.
Exploration of the Saturn system by spacecraft began
with the Pioneer 11
flyby in 1979, followed by Voyager 1
and Voyager 2 in 1980 and 1981, respectively. Pioneer 11
data yielded new insight into the magnetic
field generated
by the planet and enabled the discovery of the F Ring. The
Voyager spacecraft returned the
first clear images that
revealed the great geologic diversity of Saturn
'
s satellites.
The paths of Voyagers 1 and 2 were planned to use a
gravitational
“
boost
”
from Jupiter to speed them on their
way to Saturn. Voyager 1
flew closer to Jupiter and received
a greater boost in speed that allowed it to arrive at Saturn in
November 1980, nine months earlier than Voyager 2.Aimed
s Moon as a target.
During its
fly-through of the asteroid belt in early 2000,
images were taken of asteroid 2685 Masursky to determine
its diameter of 15
-
20 km. Later that same year, the Cassini
spacecraft
flew past Jupiter and obtained new data on the
atmospheric structure of the planet and some characteristics
ofitsrings,aswellasimagesofIo
'
s volcanic eruptions
from which movies were made.
The Cassini orbiter and attached Huygens probe reached
Saturn in mid 2004. Later that year, on December 25, the
probe was released from the orbiter, and it reached Titan
'
s
surface on January 14, 2005. As it descended through
Titan
'
s atmosphere, various measurements of its temper-
ature, pressure, and composition were made, as well as
obtaining descent images. On reaching the surface, some
instruments continued operation, including the cameras that
returned the
first images from the surface of an outer planet
satellite.
'
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