The Saturn system - Introduction to Planetary Geomorphology - page 188

Figure 9.21. This mosaic of Cassini images is
centered on the south polar region of
Enceladus and shows the so-called “ tiger-

stripe terrain consisting of huge, parallel

fractures (NASA PIA12783).

”

and on-board compositional analysis of materials col-
lected by the orbiter during its passage through the
plumes provide critical information on the nature of the
cryovolcanic eruptions. The components in the plumes
are ice grains containing salt, water vapor, nitrogen,
carbon dioxide, ammonia, methane, and other organic
compounds.
The eruptive jets are associated with the “ tiger-stripes, ”
which consist of four parallel fractures, each of which is
~130 km long and 2 kmwide and flanked by ridges as high
as 0.5 km and as wide as 4 km. Remote sensing of the
terrain indicates the presence of chucks of ice as large as
10 m and coarsely crystalline ice grains not seen else-
where on Enceladus. Because coarse ice grains are short-
lived in the Enceladus environment, these deposits are
estimated to be younger than 1,000 years. Cassini meas-
urements over the fractures show temperatures as high as
157 K, considerably elevated over the average for the
surface of 68 K. Coupled with plume observations, most
planetary scientists consider the eruptions (or geysers) to
be derived from one or more subsurface pockets of high-
pressure liquid water. A compelling argument has been
made by Dennis Matson and other Cassini scientists that
Enceladus seawater contains dissolved carbon dioxide

and other gasses that exsolve close to the surface, produc-
ing explosive plumes much like zzy soda water once the
cap is taken off.
Enceladus, along with Europa and Titan, is a future
target in the exploration of life in the outer Solar System.
The presence of a rich organic soup, the likelihood of
liquid water (either in pockets in the icy crust or in a larger
subsurface ocean), and the presence of internal heat com-
bine to suggest an environment, or habitat, favorable to
astrobiology. Regardless of the outcome of its astrobio-
logical exploration, Enceladus remains important for geo-
logic study.

9.7 Intermediate-size satellites

For the following moons we have suf cient data to
describe their geology, and they are listed in order of
distance from Saturn, beginning with Mimas.

9.7.1 Mimas

Mimas, like Enceladus, was discovered by Herschel in
1789. This heavily cratered object ( Fig. 9.22 ) orbits Saturn