Download 14. 1 A Travel Guide to the Outer Planets 14.2 Jupiter 14.3 Saturn

CHAPTER
14
COMPARATIVE PLANETOLOGY OF THE OUTER PLANETS
Topic Summaries
14. 1 A Travel Guide to the Outer Planets
What are the properties of the Jovian planets?
oblateness The flattening of a spherical body, usually caused by rotation.
liquid metallic hydrogen A form
• The Jovian planets-Jupiter, Saturn, Uranus, and Neptune-are large, low -d ensity w orlds rich in hydrogen and helium.
of liquid hydrogen that is a good
• The atmospheres of the Jovian planets are marked by cloud belts parallel to
their equators.
in the interiors of Jupiter and Saturn .
Jupiter and Saturn, usually called "gas giants;' are composed mostly of liquid hydrogen and might instead be called "liquid giants:' Uranus and Neptune contain
water in liquid and solid form and therefore are sometimes called "ice giants:'
All of the Jovian worlds have large systems of satellites and ring s that have had
complex histories.
electrical conductor, inferred to exist
magnetosphere The volume of
space around a planet within which
the motion of charged particles is
dominated by the planetary magnetic
field rather than the solar wind.
belt-zone circulation The
14.2 Jupiter
Jupiter's atmosphere contains three layers of clouds formed of hydrogen-rich
molecules such as ammonia and water.
atmospheric circulation typical of
Jovian planets in which dark belts
and bright zones encircle the planet
The clouds are in bands parallel to the equator called zones and belts. Zones
are high-pressure regions of rising gas, and belts are low er-pressure areas of
sinking gas.
parallel to its equator.
Models indicate that Jupiter has a core of eavy e emen · and a de p._man e of
liquid metallic hydrogen in which the pl anet's magnetic field is gener~ted .
origin I direction of the light's travel.
The magnetic field around Jupiter traps h1gh- ne gy pa, tides from the s
form intense radiation belts.
forward scattering The optical
roperty of finely divided particles
Roche limit The minimum distance
~between a planet and a satellite that
can hold itself together by its own
Jupiter must be very hot inside because heat is flowing out of it.
gravity. If a satellite's orbit brings it
Jupiter's ring is composed of dark particles that strongly forward-scatter light,
which means the particles are very small. They are probably composed of dust
resulting from meteorite impacts on moons.
within its planet's Roche limit, tidal
Jupiter's ring, like all of the rings in the solar system, lies inside the planet's
Roche limit, where moons would be torn apart or unable to form .
How do you know that some moons have been geologically active?
Grooves on Ganymede, smooth ice and cracks on Europa, and active volcanoes
on lo show that tidal heating has made th ese moons active.
14.3 Saturn
Saturn is less dense than water and contains a small core and less metallic
hydrogen than Jupiter.
• The cloud layers on Saturn occur at the same temperature as those on Jupiter,
but, because Saturn is further from the sun and colder, the cloud layers are
deeper in the hydrogen atmosphere below a layer of methane haze.
forces will pull the satellite apart.
tidal heating The heating of a
planet or satellite because of friction
caused by tides.
shepherd satellite A satellite that,
by its gravitational field, confines
particles to a planetary ring.
ovoid The oval features found on
Miranda, a satellite of Uranus.
occultation The passage of a larger
body in front of a smaller body.
dwarf planet A body that orbits
the sun, is not a satellite of a planet,
How are planetary rings formed and maintained?
is massive enough to pull itself into
•
a spherical shape but not massive
•
Saturn's rings are composed of icy particles ranging in size from boulders to
dust. In some regions the ice is purer than in other regions.
Grooves and other features in the rings can be produced by resonances w ith
moons or by w aves that propagate through the rings.
Narrow rings and sharp ring edges can be confined by shepherd satellites.
enough to clear out other bodies in
and near its orbit. For example, Pluto,
Eris, and Ceres.
plutino One of the icy Kuiper belt
objects that, like Pluto, is caught in a
3:2 orbital resonance with Neptune.
Topic Summaries
Review Guestions
1. How can Jupiter have a liquid
interior and not have a liquid
surface?
• The rings are short lived. They cannot be as old as their planet and must be
replenished now and then with material from meteorites and comets colliding with moons.
2. How does the dynamo effect
account for the magnetic fields
of Jupiter and the other Jovian
planets?
•
3. Why are the belts and zones on
Saturn less distinct than those
on Jupiter?
Titan has a cold, cloudy nitrogen and methane atmosphere. Sunlight entering
Titan's atmosphere can convert methane into complex carbon-rich molecules
to form haze and particles that settle out to coat the surface with dark organic goo. Methane lakes may have been detected on Titan's surface in radar
images made by the Cassini probe.
•
Enceladus has a light surface with some uncratered regions. Geysers of water
and ice spray from the south polar region and provide ice particles to theE ring.
4. Explain why geological activity
on Jupiter's moons varies with
distance from the planet.
14.4 Uranus
5. What makes Saturn's F ring
and the rings of Uranus and
Neptune so narrow?
6. What is the evidence that
Enceladus is geologically
active?
7. Why is the atmospheric activity
of Uranus unlike that of Jupiter,
Saturn, and Neptune?
How do the two smaller Jovian worlds-Uranus and Neptune-differ from
their more massive siblings?
•
Uranus is much less massive than Jupiter, and its internal pressure cannot
produce liquid hydrogen. It has a heavy-element core and a mantle of slushy
or solid ice and rock below a hydrogen-rich atmosphere.
• The atmosphere of Uranus is almost featureless at visual wavelengths with a
pale green-blue color.
•
The larger moons of Uranus are icy and heavi ly cratered, with some signs of
past geological activity.
8. What are the seasons o
Uranus like?
9. Why are Uranus and Neptune
greenish-blue and blue,
respectively?
10. What evidence is there that
Neptune's moon Triton has
been geologically active
recently?
11 . What evidence indicates that
catastrophic impacts have
occurred in the solar system's
past?
12. Two images of Uranus show
it as it would look to the eye
and through a red filter that
enhances methane clouds in
the northern hemisphere. Why
didn't Voyager 2 photograph
the northern hemisphere?
What do these features tell you
about atmospheric circulation
on Uranus?
M
14.5
Neptune is an ice giant like Uranus with little or no liquid hydrogen in
its interior.
The atmosphere of Neptune, marked by faint patterns of belt- zone circulation, is rich in hydrogen and colored blue by traces of methane.
•
Neptune's satellite system is odd in that Nereid has an extremely elliptical
orbit and Triton orbits backwards.
Triton is icy with a thin atmosphere and frosty polar caps. Smooth areas suggest past geological activity, and dark smudges mark the location of active
nitrogen geysers.
• The rings of Neptune are made of dark icy particles in narrow hoops. Neptune's rings contain arcs produced by the gravitational influence of one or
more moons.
14.6 Pluto
•
Pluto is a small, icy world with three moons, one of wh ich is relatively large.
The moons are in orbits highly inclined to Pluto's orbit around the sun. Pluto
has a thin atmosphere.
Why do astronomers classify Pluto as a "dwarf planet"?
•
Pluto is related to other icy objects in the Kuiper belt, some of which are
larger than Pluto.
Pluto does not meet all the IAU's criteria to be classified as a planet: though
spherical, it hasn't cleared its orbital zone of smaller objects, making it a
dwarf planet.