Saturn
Size and mass:
This gives a density of 95/(9)3 * (density)E
= 0.1 (density)E. That amounts to 690 kg/m3, less
than that of water.
The density suggests that Saturn is mostly made of hydrogen and helium gas,
with some water and other molecules that would have come from ``ices'' in
the early solar system, plus some molten rock. This is similar to Jupiter.
Why less dense than Jupiter? Saturn has 1/3 the mass of Jupiter (recall
that Jupiter's mass is about 320 ME. Thus one expects the
gas to be less compressed.
Visible atmosphere: bands but not so colorful as Jupiter.
Saturn's rings
Saturn has a famous ring system.
- They were first noticed by Galileo, but all he could see was that
Saturn wasn't round.
- Christian Huygens, The Hague, 1629 - 1695, made telescopic observations of Saturn and explained why sometimes one could see the bulges and sometimes not. He deduced that the bulges
were thin rings that are sometimes seen edge on.
- James Clerk Maxwell deduced in 1857 that the rings couldn't be solid or they would break.
Let's look at the rings.
- Here are Saturn's rings.
- Here they are as seen from in back .
Note that they are partly transparent.
- Here they are as seen edge on
but the Hubble Space Telescope. Note that they are very thin.
- In a
close-up view with some color
enhancement, you can see that there are lots of large and small
divisions among rings, as well as transient "spokes."
Other planets have rings too.
What could they be?
- Not solid. (Too weak; and we can see through them.)
- Not a gas. (They would just spread out.)
- Many small particles seems OK.
- Ice and rock are easily available.
- (Indirect) size measurements by Voyager spacecraft suggests that most of the particles are snowball size (10 cm), with a range from snowflake size to Willamette Hall size.
Why rings?
What would be wrong with just an unorganized swarm of particles?
Why not moons?
ASTR 121 Home
Davison E. Soper, Institute of Theoretical Science,
University of Oregon, Eugene OR 97403 USA
soper@bovine.uoregon.edu
