Astronomy a beginners guide to the universe 8th CHaisson mcmillan chapter 08

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Lecture Presentation

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Chapter 8 Moons, Rings, and Plutoids

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Units of Chapter 8

• The Galilean Moons of Jupiter

• The Large Moons of Saturn and Neptune

• The Medium-Sized Jovian Moons

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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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• This image shows Jupiter with two of its Galilean moons

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• The Galilean moons and their orbits

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• Their interiors

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• Io is the densest of Jupiter’s moons, and the most geologically active object in the solar system

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• 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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• 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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• 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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• 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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• Infrared image of Titan, showing detail

and possible icy volcano

• There are few craters, consistent with

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• The Huygens lander took these images of the surface of Titan.

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• Trace chemicals in Titan’s

atmosphere make it chemically

complex

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• 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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• Moons of Saturn, in natural color

• Note the similarities, as well as the large crater on Mimas

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• Moons of Uranus and Neptune

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• 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 rings are not solid; they are composed of small rocky and icy particles

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• Our view of Saturn’s rings changes as the planet moves in its orbit

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• All observed ring systems are within this limit

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• 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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• Jupiter has been found to have a small, thin ring

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• Uranus has nine thin rings The inset (top) shows the Epsilon ring

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• Two shepherd moons keep the Epsilon ring of Uranus from diffusing away

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• Neptune has five rings, three narrow and two wide

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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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• Charon’s orbit is at an angle of 118º to the plane of Pluto’s orbit

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• 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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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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