Download Rings, Moons, and Pluto The Jupiter System The Orbits of Jupiter`s

Rings, Moons, and Pluto
The Jupiter System
• All the giant planets have moons that orbit them
•
•
•
•
• Jupiter has 16 satellites
like planets in a miniature solar system
There are 60 satellites known in the outer solar
system
Several of the moons are larger than Pluto and
have atmospheres of their own
Pluto resembles these satellites more that it
resembles the other 8 planets
All the giant planets have rings
Q
Q
4 large moons discovered by Galileo
Callisto, Ganymede, Europa, Io
X Europa and Io are about the size of the Moon
X Ganymede and Callisto are bigger than Mercury
X
Q
Remaining 12 moons are much smaller
The inner 4 orbit inside the orbit of Io
X Of the remaining 8 small moons
X
+
Rings consist of billions of small particles or moonlets
+
+
ISP 205 - Astronomy Gary D. Westfall
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4 have highly inclined orbits
4 have retrograde orbits
May be captured objects
ISP 205 - Astronomy Gary D. Westfall
The Orbits of Jupiter’s Moons
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The Saturn System
• Saturn has 19 known satellites
• Simulation
Q
The largest is Titan, which is almost as big as Juptier’s
Ganymede
X
Q
Q
Q
Titan is the only moon with a substantial atmosphere (more
later)
6 other moons have regular orbits
Several moons orbit near the rings
2 distant, irregular moons, one retrograde
• The rings of Saturn are spectacular
Q
Q
ISP 205 - Astronomy Gary D. Westfall
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Broad, flat, few gaps
Rings are a collection of icy fragments with sizes
ranging from a ping pong ball to a basketball
ISP 205 - Astronomy Gary D. Westfall
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The Orbits of Saturn’s Moons
The Uranus System
• The ring and satellite system of Uranus is
• Simulation
tilted 98 degrees just like the planet itself
Q
11 rings
Only discovered in 1977
X Narrow ribbons with broad gaps
X Composed of icy, dark material
X
Q
18 moons
The 5 largest satellites are similar to the 6 regular
satellites of Saturn
X The 13 smaller moons are very dark
X
• Simulation
ISP 205 - Astronomy Gary D. Westfall
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ISP 205 - Astronomy Gary D. Westfall
The Neptune System
Q
Q
6 regular satellites close to the planet and two
irregular satellites farther out
Triton is a relatively large moon in a retrograde
orbit
Triton has an atmosphere and active volcanoes
• Neptune has rings
Q
Q
Narrow and faint
Composed of dark, icy material
• Simulation
ISP 205 - Astronomy Gary D. Westfall
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The Largest Satellites
• Neptune has 8 satellites
Q
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Name
Diameter
(km)
Mass
(Moon=1)
Density
(g/cm3)
Reflectivity
(%)
Moon
3476
1.0
3.3
12
Callisto
4820
1.5
1.8
20
Ganymede
5270
2.0
1.9
40
Europa
3130
0.7
3.0
70
Io
3640
1.2
3.5
60
Titan
5150
1.9
1.9
20
ISP 205 - Astronomy Gary D. Westfall
Lecture 13
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The Ice of Callisto
Callisto, an Ancient and Primitive World
• Callisto orbits Jupiter at a distance of 2 million
• The surface of Callisto is composed of water ice
• This ice is much colder than ice on Earth and does
km and circles Jupiter in 17 days
• Callisto has the same rotational period as orbital
period like the Moon
• The surface temperature of Callisto is -140
degrees centigrade
• Callisto is about the same size as Mercury but
with only 1/3 the mass of Mercury
Q
not flow like Earth’s glaciers
• The surface of Callisto is covered with impact
craters
Q
• Generally the craters on Callisto resemble the
crater on the Moon
Callisto has much less rocky materiel than Mercury
Q
• Callisto is undifferentiated
Q
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Results from sublimation of water leaving behind a dusty
material
ISP 205 - Astronomy Gary D. Westfall
Portrait of Callisto
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Ganymede, the Largest Satellite
• About 1/4 of the surface of Ganymede is cratered
• The remaining surface area was formed more recently
• Callisto was
a nymph,
beloved of
Zeus and
hated by Hera.
Hera changed
her into a bear
and Zeus then
placed her in
the sky as the
constellation
Ursa Major.
Q
Sparse, fresh craters
X
About 1 billion years old
+
Younger than the lunar maria or martial plains
• Ganymede is differentiated
Q
Q
Has a rocky core about the size of the Moon
Has a magnetic field
• The young surface is the result of tectonic and volcanic
forces
Q
Q
Q
Q
ISP 205 - Astronomy Gary D. Westfall
When one looks in detail at the crater, they show
erosion
X
Callisto was frozen solid before differentiation was
completed
ISP 205 - Astronomy Gary D. Westfall
There is no geological activity on Callisto
Lecture 13
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Some features formed when the crust cracked and water
flooded craters
Mountain ranges were formed from compression of the crust
Impact craters were split and pulled apart
May have been caused by tidal forces from Jupiter
ISP 205 - Astronomy Gary D. Westfall
Lecture 13
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Portrait of Ganymede
Europa, the Satellite with an Ocean
• Europa is similar to the Moon
• Ganymede
was a Trojan
boy of great
beauty whom
Zeus carried
away to be cup
bearer to the
gods.
Q
• Heat from the forming Jupiter combined with continuous
•
•
heating from tidal forces evaporated most of the water on
Europa
However, Europa retains an ice-covered surface
There are very few impact craters on Europa
Q
Q
there is liquid water under the surface
Heat is derived from tidal forces
Q
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Io, a Volcanic Satellite
• Io is the inner most satellite of Jupiter
• Similar to the Moon in size and density
• Io has the highest level of volcanism in the solar
• Europa was a
Phoenician princess
abducted to Crete by
Zeus, who had
assumed the form of
a white bull, and by
him the mother of
Minos.
•
•
•
•
•
Lecture 13
May be sufficient for primitive life
ISP 205 - Astronomy Gary D. Westfall
Portrait of Europa
ISP 205 - Astronomy Gary D. Westfall
Surface is younger than a few million years
Europa is better able to erase impact craters than Earth
• Cracks and long ridges on the icy surface suggest that
•
ISP 205 - Astronomy Gary D. Westfall
Predominantly rock
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system
Volcanic eruptions are visible on the surface of Io
The lava is similar to lava on Earth
Sometimes the lava comes in contact with frozen
layers of sulfur and sulfur dioxide and produces
huge plumes
The surface of Io is constantly changing
Tidal heating keeps Io active
ISP 205 - Astronomy Gary D. Westfall
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Portrait of Io
Titan, a Satellite with an Atmosphere
• Io was a
• Titan, the largest satellite of Saturn, was discovered in
maiden who
was loved
by Zeus
(Jupiter)
and
transformed
into a heifer
in a vain
attempt to
hide her
from the
jealous
Hera.
•
•
1655 by the Dutch Astronomer Christian Huygens, the
first moon to be found after Galileo saw the four large
moons of Jupiter
Titan is roughly the same size as Callisto and Ganymede
but its composition is unknown
Titan has a substantial atmosphere
Q
Q
Q
Has a pressure 1.6 times Earth
Mostly nitrogen
Contains other gases
X
X
X
ISP 205 - Astronomy Gary D. Westfall
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The Structure of Titan’s Atmosphere
Carbon dioxide, methane, ethane, propane
Hydrogen cyanide, cyanogen, cyanoacetylene
Active chemistry thought to be the progenitor of life on Earth
ISP 205 - Astronomy Gary D. Westfall
• In Greek
mythology the
Titans were a
family of giants,
the children of
Uranus and Gaia,
who sought to
rule the heavens
but were
overthrown and
supplanted by the
family of Zeus.
Titan
• The surface temperature is about 90 K
Methane can exist as solid, liquid, gas at these
temperatures
• Organic compounds are stable in Titan’s
atmosphere
Q
May hold chemical history dating back billions of
years
• Cassini and Huygens will try to find some
answers in 2004
ISP 205 - Astronomy Gary D. Westfall
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Portrait of Titan
• Titan has multiple layers of clouds
• These clouds completely obscure the surface of
Q
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ISP 205 - Astronomy Gary D. Westfall
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Triton and its Volcanoes
Portrait of Triton
• Triton is the largest satellite of Neptune
• Triton has a diameter of 2720 km and a density of 2.1
• In Greek
mythology,
Triton is a god
of the sea, the
son of Poseidon
(Neptune);
usually
portrayed as
having the head
and trunk of a
man and the tail
of a fish.
g/cm3
Q
Suggests 75% rock and 25% water ice
• The surface of Triton is very cold
Q
35 to 40 K
• The surface of Triton is made of frozen water, nitrogen,
•
methane, and carbon monoxide
Impact craters on Triton are erased by “lava” flows
Q
Melted ices
• The southern pole of Triton is covered with a polar ice
cap
Q
In summer, the ice cap is heated and geysers are created 10 km
high
ISP 205 - Astronomy Gary D. Westfall
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ISP 205 - Astronomy Gary D. Westfall
Discovery of Pluto
•
• Pluto’s orbit has a large inclination to the ecliptic (17°)
• Pluto’s orbit takes it closer to the Sun than Neptune but
rather than having a good prediction of where to look as
was the case for Neptune
Percival Lowell spent the last 10 years of his life (he died
in 1916) searching unsuccessfully for the ninth planet
In 1930, Clyde Tombaugh found the ninth planet after an
exhaustive search using photographic plates and the
blinker method
Q
Q
•
•
•
there is no chance of collision because of the angle of
inclination
Pluto requires 248.6 years to circle the Sun
Pluto’s rotational axis is tilted 90 degrees similar to
Uranus
Pluto has a moon, Charon
Q
Tombaugh worked at the Lowell Observatory
Used a camera donated by Lowell’s brother
Q
Q
• Recent measurements show there are no more planets
Q
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Pluto’s Motion and Satellite
• Pluto was discovered through a careful systematic search
•
Lecture 13
Retrograde orbit in the ecliptic (not along Pluto’s equator)
About half the size of Pluto
Orbital period and rotational period are the same as Pluto’s
rotational period
• When Pluto is close to the Sun, it’s atmosphere gets
IRAS, Voyager, Pioneer
thicker
ISP 205 - Astronomy Gary D. Westfall
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ISP 205 - Astronomy Gary D. Westfall
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The Origin of Pluto
Portrait of Pluto and Charon
• Pluto is different from the other planets
• Pluto’s orbit and composition is very different
from the other outer planets
• Pluto resembles the moons rather than the planets
• The presence of Charon is puzzling
• Some astronomers speculate that the strange
orbits of Pluto, Charon, Nereid, and Triton are the
result of violent collisions during the early history
of the outer solar system
Photo taken by the Hubble
Space Telescope
• In Roman mythology, Pluto (Greek: Hades) is the god of the
•
ISP 205 - Astronomy Gary D. Westfall
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Planetary Rings
underworld.
Charon is named for the mythological figure who ferried the dead
across the River Styx into Hades (the underworld).
ISP 205 - Astronomy Gary D. Westfall
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The Rings of the Giant Planets
• All four of the giant planets have rings
• The rings are made of billions of individual
fragments each orbiting the planet
• There are two formation possibilities
Q
Breakup
X
Q
The tidal force of the
large planet destroyed
existing moons
Prevention
X
The tidal forces of the
large planet prevented
material from
coalescing into
moons
ISP 205 - Astronomy Gary D. Westfall
Lecture 13
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ISP 205 - Astronomy Gary D. Westfall
Lecture 13
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The Rings of Saturn
Portrait of Saturn and its Rings
• The rings of Saturn are
Photo of Saturn
and its rings
taken by
Voyager 2
very broad and
extraordinarily thin
Q
Q
70,000 km wide
20 m thick
• Ring particles are
•
•
composed of water ice
with sizes ranging from
sand to house-size
boulders
Saturn has three main
rings, A, B, C
Saturn has narrow rings
also that resemble those
of Uranus and Neptune
ISP 205 - Astronomy Gary D. Westfall
Dione
Rhea
• In Roman mythology, Saturn is the god of agriculture. The associated Greek
god, Cronus, was the son of Uranus and Gaia and the father of Zeus (Jupiter).
Lecture 13
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ISP 205 - Astronomy Gary D. Westfall
The Rings of Uranus and Neptune
Lecture 13
Satellite Ring Interactions
• The rings of Uranus are narrow and black making
• Gravitational resonances with small inner moons
them almost invisible from Earth
• The 9 main rings were discovered by watching a
star pass behind Uranus
• Two more rings were discovered by Voyager in
1986
• The outermost ring is the Epsilon Ring
cause structure in rings and may be responsible
for the existence of the rings
• The narrow F ring of
Saturn shows strands with
bends and kinks
Q
Q
Contains more mass than the other rings combined
• Rings are made of black material
Q
Q
May be carbon or some hydrocarbon
Similar to its ten smaller inner moons
ISP 205 - Astronomy Gary D. Westfall
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Must be under the
influence of two shepherd
moons, Pandora and
Prometheus
• Narrow gaps in Saturn’s rings are associated with
small moons that clear lanes in the ring material
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ISP 205 - Astronomy Gary D. Westfall
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