1. The Giant Planets
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2. Jovian Worlds Saturn Neptune Uranus Jupiter 18 July 2005
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3. Missions to Outer Solar System
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4. Early Exploration of Outer Solar System
Pioneers 10 & 11 were launched in 1972 & 1973
Can they navigate through the asteroid belt?
What are the radiation hazards in Jupiter’s enormous magnetosphere?
Pioneer 10 flew by Jupiter in 1973 and then sped outward toward the edges of the solar system
Pioneer 11 flew by Jupiter in 1974 and was diverted towards Saturn, which it reached in 1979
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5. Further Exploration of Outer Solar System
Voyagers 1 & 2 were launched in 1977
They carried 11 scientific instruments, including cameras, spectrometers, and devices for measuring magnetospheres
Their missions were highly productive
Voyager 1
reached Jupiter in 1979, and used a gravity assist from Jupiter to reach Saturn in 1980
Voyager 2
reached Jupiter four month later than Voyager 1
used gravity assists to reach Saturn in 1981, Uranus in 1986, and Neptune in 1989
These multiple gravity-assisted flybys were possible thanks to the approximate alignment of the planets
Such an alignment occurs about once every 175 years
Voyager
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6. Recent Exploration of Jupiter
For a detailed study of a planet, spacecraft that can go into orbit around the planet are necessary
Flybys of the planet are not adequate
The Galileo spacecraft was launched from the space shuttle Atlantis in 1989 and arrived at Jupiter in 1995
It began its investigations by deploying a small entry probe for direct studies of Jupiter’s atmosphere
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7. Galileo Spacecraft
In September 2003, the Galileo spacecraft ended its mission by plunging into Jupiter’s atmosphere
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8. Galileo’s Entry Probe had a mass of 339 kg
plunged into Jupiter’s atmosphere at a shallow angle and a speed of km/s
was slowed down by atmospheric friction
the temperature of its heat shield reaching 15,000°C
as its speed dropped to 2500 km/h, jettisoned the remains of its shield and deployed a parachute for a gentler descent in the atmosphere (animation)
transmitted data to the Galileo orbiter, for retransmission to Earth
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9. Some Results of Galileo Mission
A satellite (Dactyl) of an asteroid (Ida) was discovered
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 was found than anticipated
The individual lightning events, however, are about ten times stronger on Jupiter than on the Earth
The helium abundance in Jupiter is very nearly the same as that in the Sun (24% compared to 25%)
Possible evidence for liquid-water ocean under Europa's ice was found
Website

10. Recent Exploration of Saturn
Saturn, with its spectacular rings and many moons, is intriguing for many reasons
The Cassini spacecraft was launched 1997 and reached Saturn in 2004
It deployed the Huygens probe into Saturn’s moon Titan in January 2005
Titan is of particular interest to scientists because it is one of the few moons in our solar system with its own atmosphere
Animation

11. Basic Facts about Jovian Planets
They
are at large distances from the Sun
have long orbital periods
rotate (spin) very fast
Jupiter and Saturn have many similarities in in composition and internal structure
Uranus and Neptune
are smaller than the other two
differ from the other two in composition and structure

12. Appearance of Jovian Planets
Only the atmospheres of the giant planets are visible to us
The atmospheres are composed mainly of hydrogen and helium
The uppermost clouds of Jupiter and Saturn are composed of ammonia (NH3) crystals
The upper clouds on Neptune are made of methane (CH4)
Uranus has no obvious clouds, only deep and featureless haze
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13. Rotation of Jovian Planets
How does one determine the rotation rates of the giants?
For Jupiter
1st option: use dynamic surface features (storms)
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
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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14. Seasons on the Giants Jupiter’s spin axis is tilted by 3°
It has no seasons to speak of
Saturn’s axis is tilted by 27° and Neptune’s 29°
Both have seasons
Uranus’ axis is tilted by 98°
practically orbiting on its side
its rings and satellites following the same pattern
causing it to have very strange 21-year seasons!!!
Uranus’s odd tilt could have been the result of a giant impact in its past
Seasons on Uranus

15. Infrared Image of Uranus
South pole marked with +

16. Giant Pressures on Giant Planets
Astronomers believe that the interiors of Jupiter and Saturn are composed mainly of hydrogen (H) and helium (He)
Their precise internal structure is difficult to predict
Because the planets are enormous, the H and He in their centers are probably compressed tremendously
Theoretical models predict that Jupiter has
a central pressure of more than 100 million bars
a central density of 31 g/cm3
The Earth by contrast has 4 million bars and 17 g/cm3 in its center
Giant planets imply giant pressures!!
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17. Consequences of Enormous Pressure
A few thousand km below Jupiter and Saturn’s visible clouds, hydrogen is changed from a gaseous to a liquid state
Still deeper, the liquid hydrogen is further compressed and begins to act like a metal
On Jupiter, most of the interior is probably liquid metallic hydrogen!
Since Saturn is less massive, it has only a relatively small volume of metallic hydrogen
Most of its interior is liquid, but not metallic
Neptune and Uranus are probably too small to liquefy hydrogen
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18. More about Composition
Detailed analyses of their gravitational fields suggest that each of the giant planets has a core composed of heavier materials
The core may have been the original rock-and-ice body that formed before gas was captured from the surrounding nebula
The pressure in the core is in the tens of millions of bars
At such a pressure, rock and ice do not assume their familiar forms

19. Internal Heat Sources
Because of their large sizes, all the giant planets are believed to be strongly heated during their formation
The contraction due to gravity produced heat
Being the largest, Jupiter was the hottest
Some of this primordial heat still remains inside them
Giant planets may also generate energy internally by slowly contracting
Even a small amount of shrinking can generate significant heat
These internal sources of heat may raise the temperatures in the interiors and atmospheres above the temperatures due to the Sun’s heat
Jupiter has the largest internal source of heat
Most of it is probably primordial heat
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20. Magnetic Fields All four giant planets have strong magnetic fields
Their associated magnetospheres are large
They extend for millions of km in space
Jupiter’s field was discovered in the late 1950s
Radio waves were detected from Jupiter
They were produced by electrons circulating in its magnetosphere by a process called synchrotron emission
The magnetic fields of Saturn, Uranus, and Neptune were discovered by flyby spacecraft
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21. Atmospheres of Giant Planets
Only their atmospheres are directly observable from space
They show dramatic examples of weather patterns
Storms on these planets can be larger in size than the Earth!
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22. Atmospheric Composition of Jovian Planets
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
This was first shown by Voyager’s far-infrared measurements by
There is less helium in Saturn’s atmosphere
The most precise measurements of composition were made on Jupiter by Galileo’s entry probe
Since these planets have no solid surfaces, their atmospheres are representative of their general compositions
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23. Clouds on Jovian Planets
Jupiter’s clouds are spectacular
ranging in color from white to orange to red to brown
Movie
The explanation for the colors remains a mystery
Saturn’s clouds are more “subdued” in color
They have nearly uniform butterscotch hue
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24. Atmospheric Structure of Jovian Planets
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25. Winds and Weather
The jovian planets’ atmospheres have many regions of high and low pressure
Air flow between these regions sets up wind patterns distorted by the fast rotation of the planet
The wind speeds are measurable by tracking cloud patterns
The weather patterns are different from Earth’s
Giant planets spin much faster than Earth
Rapid rotation smears out air circulation into horizontal (east-west) patterns parallel to the equator
No solid surface
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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26. Winds on 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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27. Giant Storms on Giant Planets
There are many storms on the giant planets
superimposed on the regular circulation patterns
The most prominent storms are large oval-shaped high-pressure regions on both Jupiter and Neptune
The most famous is Jupiter’s Great Red Spot
in the southern hemisphere
30,000 km long (when Voyager flew by)
present since first seen years ago
changing in size, but never disappearing
Movie
From Voyager 1 in 1979