Chapter 14 Jupiter and Saturn:
Jupiter is the largest planet in the solar system. It is larger than all the other planets put
together. It has more than 60 moons. Four of which would be considered large. Jupiter is
about 5Au from the Sun.
Saturn is the second largest planet in the solar system. It is about 80 percent the diameter
of Jupiter and 1/3 of Jupiter’s mass. Saturn has one large Moon (Titan). Saturn is about
10 AU from the Sun. Saturn’s rings are composed many thin rings each orbiting at its
own speed. The closer the ring is to the planet, the faster the material in that ring is
orbiting.
Jupiter and Saturn exhibit differential rotation.
1) Why is the best month to view Jupiter different from one year to the next? Jupiter is a
superior planet (what does that mean?) so it is best seen at opposition. As Jupiter moves
around its orbit it takes about 13 months for the Earth to come around and “lap” Jupiter
(get into opposition again). So Jupiter is best seen about a month later each successive
year.
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3) What is going on in Jupiter’s red spot? Jupiter’s red spot is a rotating storm that is like
a wheel between two bands of air moving in opposite directions. Jupiter’s red spot is at
least several hundred years old.
5)What does the chemical composition of Jupiter’s atmosphere imply about the planet’s
origin. The chemical composition of the atmosphere indicates that it has about the same
percentages of hydrogen and helium as the Sun does. This supports the nebular
hypothesis that they formed fro the same cloud.
6) How do astronomers know about the deep interiors of Jupiter and Saturn? The
oblateness of Jupiter and Saturn are indicators of the sizes of their rocky cores. Their
densities also give information about this. Finally, the magnetic fields indicate they have
liquid metallic hydrogen.
7) How do Jupiter and Saturn generate their intense magnetic fields? Both planets are
rotating very rapidly (they rotate in approximately 10 hours), and they both have liquid
metallic hydrogen in their interiors.
8) Why would it be dangerous for humans to visit certain parts of the space around
Jupiter? Because Jupiter’s enormous magnetic fields trap dangerous amounts of high
energy particles that would kill a human very quickly.
9) How was it discovered that Saturn has rings? First Galileo saw lumps on Saturn, then
several decades later Christiaan Huygens used a better telescope to determine the lumps
were rings.
10)Are Saturn’s rings solid bands that encircle the planet? No they are rings of small
particles (snowball sized on average). The rings do not intermingle very much.
11) How uniform and smooth are Saturn’s rings? Actually Saturn’s rings are composed
of many thin ringlets that do not interact much, so the rings are not smooth or uniform.
12) How do Saturn’s Moons affect the rings? Some of the Moons cause gaps in the rings.
In other places the Moons shepherd the rings around the planet. The Cassini division is a
gap in the rings caused by the Moon Mimas. The F ring, however, is being shepherded
by 2 Moons that keep the ring isolated.
Reviews Questions:
1) Which planet, Mars or Jupiter, passes closer to the Earth? Mars passes closer—it
orbits between Earth and Jupiter. On which planet is it easier to see details? Well, Jupiter
is so much larger that it appears about twice as big in a telescope even though it is farther
away.
3) In what ways are the motions of Jupiter’s atmosphere like the motion of water in a
stirred pot? Jupiter’s atmosphere exhibits differential rotation in which the air at the
poles takes about 5 minutes longer to complete a rotation than the air at the equator.
4) Compare Jupiter’s chemical composition with that of the Sun. They are about the
same. This supports the nebular hypothesis.
6)Is the chemical composition of Jupiter as a whole the same as that of its atmosphere?
No, because Jupiter as a whole has heavy elements in its rocky core that are too dense to
float in its atmosphere.
7) On a warm humid day water remains in the atmosphere. If the temperature drops, the
water begins to condense out and rain to the ground. Relate this to the relatively small
amounts of Helium in Saturn’s atmosphere. Saturn’s atmosphere is cool enough that the
Helium is condensing and raining out of the atmosphere.
8) What are the belts and zones in the atmospheres of Jupiter and Saturn? The belts are
the darker areas and the zones are the lighter areas. The belts are areas where warm air is
rising, the zones are areas where higher cool air is sinking.
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11) Compare and contrast the source of energy for the motions of air in the atmospheres
of Jupiter and Saturn to that of Earth. Earth gets energy for its atmosphere from the Sun.
Jupiter and Saturn get most of the energy for their atmospheres from the internal energy
of the planet.
12) Both Jupiter and Saturn emit more energy than they receive from the Sun. Compare
the internal energy sources of the two planets that produce this emission. Jupiter and
Saturn are still warm internally from the energy they gained (from gravitational
contraction) during their formation. So both planets generate heat this way. Saturn gets
additional heat from the condensation of helium in its atmosphere. Because of this
Saturn actually produces a little more heat (“pound for pound”) than Jupiter does.
17) Why is Jupiter oblate? Because it is rotating quickly. What do astronomers learn
from the value of its oblateness? They can determine the size of the rocky core from the
planet’s oblateness.
18) What is liquid metallic Hydrogen? It is hydrogen that has been compressed enough
that it liquefies—it then takes on the characteristics of a metal. What is its significance
for Jupiter? It provides the liquid metal conductor that carries the current that produces
Jupiter’s magnetic field.
22) Explain why Saturn is more oblate than Jupiter even though Saturn rotates a little
more slowly. Saturn has less mass and so a weaker gravity so when it spins it bulges out
more at the equator.
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26) Why is Saturn’s magnetosphere less extensive than Jupiter’s? Because Saturn is
smaller, has less liquid metallic hydrogen, and is rotating a little slower.
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What effect do Saturns moons have on the rings? Saturn’s moons cause a variety of
features in the rings including gaps.
Key Words:
Belts, Brown oval, Cassini division, differential rotation, Great Red Spot, liquid metallic
Hydrogen, oblateness, oblate, ringlets, shepherd satellite, tidal force, Roche limit