Transcript 8. Moons, Rings, and Plutoids: Small Worlds Among Giants

Astronomy
A BEGINNER’S GUIDE
TO THE UNIVERSE
EIGHTH EDITION
CHAPTER 8
Moons, Rings, and Plutoids
Lecture Presentation
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Chapter 8 Moons, Rings, and Plutoids
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Units of Chapter 8
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The Galilean Moons of Jupiter
The Large Moons of Saturn and Neptune
The Medium-Sized Jovian Moons
Planetary Rings
Beyond Neptune
Summary of Chapter 8
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8.1 The Galilean Moons of Jupiter
• All four Jovian planets have extensive moon
systems, and more are continually being discovered.
• The Galilean moons of Jupiter are those observed
by the astronomer Galileo in 1610: Io, Europa,
Ganymede, and Callisto.
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8.1 The Galilean Moons of Jupiter
• This image shows Jupiter with two of its Galilean
moons.
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8.1 The Galilean Moons of Jupiter
• The Galilean moons and their orbits
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8.1 The Galilean Moons of Jupiter
• Their interiors
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8.1 The Galilean Moons of Jupiter
• Io is the densest of Jupiter’s moons, and the most
geologically active object in the solar system.
– It has many active volcanoes, some quite large.
– Io can change surface features in a few weeks.
– Io has no craters; they fill in too fast. Io has the
youngest surface of any solar system object.
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8.1 The Galilean Moons of Jupiter
• Io is very close to Jupiter and also experiences
gravitational forces from Europa. The tidal stretching
is huge, and provides the energy for the volcanoes.
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8.1 The Galilean Moons of Jupiter
• Europa has no craters; surface
is water ice, possibly with liquid
water below.
• Tidal forces stress and crack ice;
water flows, keeping surface
relatively flat.
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8.1 The Galilean Moons of Jupiter
• Ganymede is the largest moon in the solar
system—larger than Pluto and Mercury.
• It has a history similar to Earth’s Moon, but with
water ice instead of lunar rock.
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8.1 The Galilean Moons of Jupiter
• Callisto is similar to Ganymede but with heavy
cratering and no evidence of resurfacing activity.
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8.2 The Large Moons of Saturn and Neptune
• Titan has been known
for many years to have
an atmosphere thicker
and denser than Earth’s;
mostly nitrogen and
argon.
• Titan’s cloudy
atmosphere makes it
impossible to see the
surface; the picture at
right was taken from
only 4000 km away.
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8.2 The Large Moons of Saturn and Neptune
• Infrared image of Titan,
showing detail and
possible icy volcano.
• There are few craters,
consistent with active
surface.
• Complex chemical
interactions occur in
atmosphere.
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8.2 The Large Moons of Saturn and Neptune
• The Huygens lander took these images of the
surface of Titan.
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8.2 The Large Moons of Saturn and Neptune
• Trace chemicals in
Titan’s atmosphere
make it chemically
complex.
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8.2 The Large Moons of Saturn and Neptune
• Triton is in a retrograde
orbit; its surface has
few craters, indicating
an active surface.
• Nitrogen geysers have
been observed on
Triton, contributing to
the surface features.
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8.3 The Medium-Sized Jovian Moons
• Densities of these moons suggest that they are rock
and water ice.
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8.3 The Medium-Sized Jovian Moons
• Moons of Saturn, in natural color
• Note the similarities, as well as the large crater on
Mimas.
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8.3 The Medium-Sized Jovian Moons
• Moons of Uranus and Neptune
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8.3 The Medium-Sized Jovian Moons
• Miranda shows evidence of a violent past, although
the origin of the surface features is unknown.
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8.4 Planetary Rings
• The ring system of Saturn is large and complex and
is easily seen from Earth. The other Jovian planets
have ring systems as well.
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8.4 Planetary Rings
• The rings are not solid; they are composed of small
rocky and icy particles.
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8.4 Planetary Rings
• Our view of Saturn’s rings changes as the planet
moves in its orbit.
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8.4 Planetary Rings
• The Roche limit is where the tidal forces of the
planet are too strong for a moon to survive; this is
where rings are formed.
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8.4 Planetary Rings
• All observed ring systems are within this limit.
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8.4 Planetary Rings
• Voyager probes showed Saturn’s rings to be much
more complex than originally thought.
• Earth is shown on the same scale as the rings.
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8.4 Planetary Rings
• “Shepherd” moons
define the edges of
some of the rings.
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8.4 Planetary Rings
• Jupiter has been found to have a small, thin ring.
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8.4 Planetary Rings
• Uranus has nine thin rings. The inset (top) shows
the Epsilon ring.
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8.4 Planetary Rings
• Two shepherd moons keep the Epsilon ring of
Uranus from diffusing away.
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8.4 Planetary Rings
• Neptune has five rings, three narrow and two wide.
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8.5 Beyond Neptune
• Pluto was discovered in 1930. It was thought to be
needed to explain irregularities in the orbits of
Uranus and Neptune, but it turned out that there
were no such irregularities.
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8.5 Beyond Neptune
• Pluto’s moon, Charon, was discovered in 1978.
• It is orbitally locked to Pluto, and about a sixth as
large.
• Pluto also has four
smaller moons: Nix,
Hydra, Styx, and
Kerberos.
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8.5 Beyond Neptune
• Charon’s orbit is at an angle of 118º to the plane of
Pluto’s orbit.
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8.5 Beyond Neptune
• The first Kuiper belt objects were observed in the
1990s, and more than 1200 are now known. Some
of them are comparable in size to Pluto.
• These images show Eris and its moon Dysnomia.
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8.5 Beyond Neptune
• This figure shows several of the largest known
trans-Neptunian objects, now collectively called
plutoids.
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Summary of Chapter 8
• The outer solar system has 6 large moons, 12
medium ones, and many smaller ones.
• Titan has a thick atmosphere and may have flowing
rivers of methane.
• Triton has a fractured surface and a retrograde orbit.
• Medium-sized moons of Saturn and Uranus are
mostly rock and water ice.
• Saturn’s rings are complex, and some are defined
by shepherd moons.
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Summary of Chapter 8, cont.
• The Roche limit is the closest a moon can survive
near a planet; inside this limit, rings form instead.
• Jupiter, Uranus, and Neptune all have faint ring
systems.
• Pluto has five moons: Charon, Nix, Styx, Kerberos,
and Hydra.
• Dwarf planets beyond Neptune (including Pluto) are
now known as plutoids.
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