Transcript Giant Planets

The Giant Planets
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The Jovian Worlds
Saturn
Neptune
Uranus
Jupiter
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Exploration
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First spacecrafts: Pioneer 10 (1972) & 11
(1973)
• Can we navigate through the asteroid belt?
• What are the radiation hazards near the planets?
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Pioneer 10 flew by Jupiter in 1973 and flew
out the solar system
Pioneer 11 flew by Jupiter in 1974 and was
deflected towards Saturn which it reached in
1979
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Exploration
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Voyager 1 & 2 (launched 1977)
• Highly productive Missions
• Carried 11 scientific instruments
including cameras and
spectrometers, devices for
measuring magnetospheres
Voyager 2
Voyager 1
• Reached Jupiter (1979) and Saturn (1980)
• Used gravity assist towards Saturn
Voyager 2
• Reached Jupiter four month later than Voyager 1
• Reached Saturn (1981), Uranus (1986), Neptune (1989)
Multiple Flybys possible thanks to approximate
alignment of the planets
• Such an alignment occurs once in 175 years
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Exploration
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Galileo space probe
• Launched 1989
• Reached Jupiter December
•
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1995
Deployed a small entry probe
for a direct study of Jupiter’s
atmosphere
Sept. 2003, probe sent into
Jupiter’s atmosphere to end
its mission
Cassini
• Launched 1997
• Reached Saturn in 2004, now
•
in orbit
Deployed entry probe for
Titan in Jan. 2005
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Galileo Space Probe
Galileo – Jupiter Entry Probe
 Mass 339 kg
 Plunged at shallow angle into
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Jupiter at speed of 50 km/s
Slowed down by friction against
Jupiter atmosphere
• Temperature of its shield reached
15,000°C
 Speed dropped to 2500 km/h
 Deployed parachute for actual entry in the
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atmosphere
Transmitted data to orbiter, for retransmission to
Earth
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Some Results of the Galileo Mission
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The discovery of a satellite (Dactyl) of an asteroid (Ida)
Jovian wind speeds in excess of 600 km/hour (400 mph)
were detected
Far less water was detected in Jupiter's atmosphere than
estimated from earlier Voyager observations and from
models of the Comet Shoemaker-Levy 9 impact
Far less lightning activity (about 10% of that found in an
equal area on Earth) than anticipated. The individual
lightning events, however, are about ten times stronger
on Jupiter than the Earth
Helium abundance in Jupiter is very nearly the same as
its abundance in the Sun (24% compared to 25%)
Extensive resurfacing on Io due to continuing volcanic
activity since the 1979 Voyagers fly-bys
Evidence for liquid water ocean under Europa's ice
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Huygens Probe Dropped by Cassini Orbiter
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Basic Facts of Jovian Planets
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Large distances from the sun
Long periods
Jupiter and Saturn similar in composition and
internal structure
Uranus and Neptune smaller and differ in
composition and structure
Basics Properties of the Jovian Planets
Planet Distance
Period
(years)
Diameter
(km)
Mass
(Earth=1)
Density
(g/cm3)
Rotation
(hours)
Jupiter 5.2
11.9
142800
318
1.3
9.9
Saturn 9.5
29.5
120540
95
0.7
10.7
Uranus 19.2
84.1
51200
14
1.2
17.2
Neptune30.1
164.8
49500
17
1.6
16.1
(AU)
Appearance
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Only the upper atmosphere of the giant
planets is visible to us
• Astronomers believed that their interiors are
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composed primarily of hydrogen and helium
The uppermost clouds of Jupite and Saturn
are composed of ammonia (NH3) crystals
Neptune’s upper clouds are made of methane
(CH4)
Uranus has no obvious clouds, only deep and
featureless haze
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Rotation
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How does one determine the rotation rate of
the giants?
For Jupiter:
• 1st option: use dynamic surface features (storms)
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However the cloud rotation may have nothing to do with
the rotation of the mantle and core…
• 2nd option: look at periodic variations of radio
waves associated with the magnetic field produced
deep inside the planet
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This gave rotation period of 9 h 56 m
The same technique is used to measure the
rotation of other giant planets:
• Saturn has 10 h 40 m
• Uranus and Neptune have about 17 hours
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Seasons on the Giants
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Jupiter is tilted by 3o
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Saturn is tilted by 27o
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Neptune is tilted by 27o
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Uranus is Tilted by 98o
• No seasons to speak of
• Long seasons
• Long seasons
Seasons on Uranus
• Practically orbiting on its side
• Rings and satellites follow same pattern
• 21 year seasons!!!
• Why this odd tilt?
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A giant impact in the past could be the cause
Giant Planets – Giant Pressure
 Giant planets composed mainly of
hydrogen (H) and helium (He)
 But because of its enormous size, the H
and He in the center of Jupiter are
compressed enormously
• Estimated pressure: 100 million bars.
• Central density of 31 g/cm3
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Earth by contrast has 4 million bars and
17 g/cm3 in its center
 Giant Planet implies giant pressure!!
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Consequences of the Pressure
 Few thousand km below the surface,
hydrogen is in a liquid state
 Still deeper, the liquid is further
compressed and begins to act like a
metal
• On Jupiter, part of the interior is metallic
hydrogen!
 Saturn is less massive
• Most of its interior is liquid, but not metallic
 Neptune and Uranus are probably too
small to liquefy hydrogen
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More about Composition
 The planets also have a core composed
of heavier materials
• Possibly the original rock/ice bodies that
formed before
gas were
abundantly
captured by
the planets
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Internal Heat Source (1)
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Because of their large sizes, all the giant planets are
believed to be strongly heated during their formation
• Jupiter was the hottest
• Some of the primordial heat still remains
Giant planets may also generate energy internally by
slowly contracting
• Even a small amount of shrinkage can generate significant
heat
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This probably raises the temperature of the core and
atmosphere above the temperature due to the Sun’s heat
Jupiter has the largest internal source of energy
• 4x1017 W
• A cross between a planet (like earth) and a star
• Internal heat probably primordial heat
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Magnetic Fields
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All four giant planets have
strong magnetic fields and associated magnetospheres
The magnetospheres are large
• They extend for millions of km in space
Jupiter’s field was discovered in the late 1950’s
• Radio waves detected from Jupiter
• Electrons circulating in the magnetosphere produce the radio
waves by a process called synchrotron emission
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Magnetic fields of Saturn, Uranus, and Neptune
discovered by flyby spacecraft
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Magnetospheres
 Jupiter’s magnetic field is not aligned
with its axis of rotation
• It is tipped by 10o
 Uranus and Neptune have tilts of 60o
and 55o
 Saturn’s field is perfectly aligned with
its axis of rotation
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Atmospheres of the Giant Planets
 The part of the planets accessible to
direction observation
 Dramatic examples of weather patterns
• Storms on these planets can be larger than
Earth!
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Atmospheric Composition
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Methane (CH4) and ammonia (NH3) were
first believed to be the primary constituents
of the atmospheres
We know today that hydrogen and helium are
actually the dominant gases
• First based on far-infrared measurements by
Voyager
• Less helium in Saturn’s atmosphere
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Precipitation of helium? Energy source of Saturn?
• Best measurements of composition by Galileo
spacecraft (1995) upon entry to atmosphere
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Clouds and Atmospheric Structure
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Jupiter’s clouds are
spectacular in color and
size
• Color: orange, red, brown
• Fast motion
Saturn is more
“subdued”
• Clouds have nearly
uniform butterscotch
hue
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Atmospheric Structure of the Jovian Planets
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Winds and Weather
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Many regions of high/low pressures
• Air flow between these regions sets up wind
patterns distorted by the fast rotation of the
planet
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Wind speeds measurable by tracking cloud patterns
Differences with Earth
• Giant planets spin much faster than Earth
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Rapid rotation smears out air circulation into horizontal
(east-west) patterns parallel to the equator
• No solid surface
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No friction or loss of energy – this is why tropical storms
on Earth eventually die out…
• Internal heat contributes as much energy to the
atmosphere as sunlight (except for Uranus)
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Winds on The Giant Planets
 Winds on Uranus and Neptune are
rather similar to those on Jupiter and
Saturn
• True on Uranus in spite of the 98O tilt
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Storms
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Omni-present on the giant planets
Superimposed on the regular circulation
patterns
Large oval-shaped high-pressure regions on
both Jupiter and Neptune
Most famous: Jupiter’s Great Red Spot
• In the southern hemisphere
• 30,000 km long (when
Voyager flew by)
• Present since first seen 300
years ago
• Changes in size, but never
disappears
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From Voyager 1 in 1979
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Great Red Spot
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Counterclockwise rotation with rotation
period of 6 days
Similar disturbances
formed in the 1930s
on Jupiter
• Smaller circles near the
red spot
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Cause unknown
Long-lived because of
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Expected lifetime: centuries
• absence of ground
• their size
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Neptune Great Dark Spot
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First seen in 1989 by
Voyager
About 10,000-km long
17-day period
Had disappeared (faded?)
in mid 1990s
New dark spot seen in
Nov. 1994
• Faded by 1995
Do storms form and
disappear quicker on
Neptune?
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