- The Cassini Orbiter is transforming our knowledge of Saturn.
- Launched in 1997, Cassini arrived at Saturn in June 2004.
- Cassini fired a rocket engine to slow down and was captured into orbit about Saturn.
- During its four year mission Cassini will complete about 70 orbits, touring the Saturnian system using the various moon's gravity to adjust its
- Cassini is exploring the circulation and composition of Saturn's atmosphere and the structure and composition of Saturn's rings.
- It has passed near Saturn's various icy moons multiple times with a focus on Titan.
- Saturn is similar to Jupiter in size and composition (mostly
Hydrogen and Helium -- no solid surface).
- Like Jupiter, Saturn's atmosphere has a banded structure due to
rapid rotation and cloud decks of the same materials (ammonia,
ammonium hydrosulfide, and water).
- Not as much cloud contrast is apparent. The
clouds are deeper in the atmosphere and there is
a larger separation between the cloud decks. The
clouds are thus obscured by the higher altitude methane
- Saturn's atmosphere has more Hydrogen relative to
Helium than both Jupiter and the Sun???
- Has the helium begun to differentiate
out of Saturn's atmosphere and fall toward the center?
- Like Jupiter, Saturn radiates more energy than
it receives from the Sun.
- It should, however, have cooled completely
at this point due to its smaller size compared with Jupiter.
- Differentiation would provide a source of
energy to explain Saturn's internal heat source.
- Prominent rings distinguish Saturn from the other Jovian worlds.
- The rings are composed of billions of chunks of water ice ranging in
size from millimeters to meters.
- The rings are exceptionally thin. A sheet of paper is thicker relative to its size.
- Lumped together this material would
only produce a tiny moon tens of kilometers in diameter - a fact which may betray the origin of the rings.
- The particles do not collect to form a single small satellite
because they lie inside Saturn's ``Roche Limit''.
- On close examination the rings of Saturn are
composed of thousands of tiny concentric ringlets.
- The satellites clear out small gaps due to a phenomenon called ``orbital resonance.''
- A particle in a gap, for example, would orbit Saturn
3 times for every 2 orbits of one of the satellites.
- Feeling a consistent tug the particle is
removed from the gap.
- The mutual gravitational attraction of the individual ring
particles also creates ``density waves" which produce some of the
- Saturn's rings are a transient structure. They are gradually
being eroded by cosmic rays, sunlight, and solar wind.
- At the present rate of erosion they will survive only about 100 million years - suggesting that they were only recently formed.
- A small satellite being disrupted within the
Roche limit 100 million years ago may be responsible for
today's temporary rings.
Revised December 1, 2003