15.Giant Planets

7/29/2019 15.Giant Planets

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Giant Planets

Jupiter, Saturn, Uranus, Neptune


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Size Comparison

Jupiter: 318 Earth-masses, Saturn: 95, Uranus: 14.5, Neptune: 17.2

Two subclasses: Jupiter-Saturn and Uranus-Neptune


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Terrestrial planetslow mass

high density

slow rotators (24 hours)few satellites

close to Sun (1.6 AU)

Thin atmospheres

Weak or no magnetic field

Giant planetshigh mass

low densityrapid rotators (18 hours)

many satellites

far from Sun (5 AU)Thick atmospheres

Strong magnetic field


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Jupiter, Saturn, Uranus, and Neptune have all been

visited by the Voyager space probes.

Galileo was crashed into JupiterCassini is now at Saturn

Jupiter, Saturn, Uranus, and Neptune are all

massive bodiesformed in outer part of pre-solar nebula where ices

condense

growth by accretion and coalescence

Giant planets are gaseous/fluid bodies

supported by balance between pressure and

gravity: Hydrostatic equilibrium


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Solar Nebula Composition

98% of the nebula was in the form of gaseous H2 and He.

2% consisted of H2O, CH4, and NH3, (ices), and even smaller

amounts of rocks and metals (olivines, pyroxenes, iron, nickel, etc.).

Jupiter is closest to solar composition

Saturn less H2 and He

Uranus and Neptune mostly ices


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Mass-Size-Composition

The physical size of a planet depends on both its mass

and its chemical composition.


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Chemistry of a Giant Planet


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Atmospheres of Jovian Planets

Jupiter and Saturn

For both planets, methane and frozen ammonia (NH3)

crystals are common.

For Saturn, the NH3 extends over a greater depth and is

harder to see through, giving the planet a uniformly hazy

appearance

Uranus and NeptuneFor both planets only methane (CH4)

in atmospheres; NH3 completely frozen out.

Uranus and Neptune have a greenish-blue

appearance because methane absorbs red light.

Rapid differential rotation of giant planets stretches clouds into bands.


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Jupiter -- reds and browns (ammonia, sulfur compounds, methane)Saturn -- reds and yellows (ammonia, sulfur compounds, methane)

Uranus -- blues and greens (mostly from methane gas)

Neptune -- blue (from methane gas)

Colors


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At very high pressures inside Jupiter and Saturn hydrogenbegins to act like a liquid metal This provides an electrically

conducting fluid in which a magnetic field is generated.

In Uranus and Neptune the magnetic fields are generated byconvection of water, ammonia and methane.

Jupiter and Saturn have very strong magnetic fields which are

closely aligned with the planet's spin axis

The magnetic fields of Uranus and Neptune are weaker,

irregular and highly tilted with respect to the planet's rotation

axis.

Giant Planet Magnetic Fields


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Magnetospheres of Giant Planets


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Jupiters Great Red Spot

The Great Red Spot isa huge storm

measuring 12,000 by

25,000 km (7,500 by

15,500 miles), which isbig enough to hold two

Earths side by side.

While Jupiter's cloud

patterns can change

within hours or days

like on Earth, the Spot

has lasted for over 300

years.


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Jupiters Interior


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Jupiter radiates 1.6 times a much energy as falls on itfrom the Sun. Thus, Jupiter has an internal heat source.

It is thought that much of this heat is residual heat left

over from the original collapse of the primordial nebula toform the Solar System, but some may come from slow

contraction.

This internal heat source is presumably responsible for

driving the complex weather pattern in its atmosphere,unlike the Earth where the primary heat source driving

the weather is the Sun.

Jupiters Internal Sources of Energy


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Discoverer: Unknown

Spacecraft Encounters:

Pioneer 11 (1979);

Voyager 1 & 2 (1980, 1981)

Cassini - Huygens (2004)

Mean Distance from the Sun: 9.539 AU

Length of Year: 29.46 Earth years

Rotation Period: 10.66 hours

Mean Orbital Velocity: 9.64 km/s (6 mi/s)

Inclination of Axis: 26.73 degrees

Diameter: 120,536 km (74,901 mi)

Number of Observed

Satellites:>25

Comparisons With Earth:

Diameter: 9.4 X Earth's

Average Distance from the

Sun:9.5 X Earth's

Mass: 95 X Earth's

Density: 0.13 X Earth's

Saturn Facts

Now 34


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There are extremely high velocity winds in the atmosphere of Saturn.

Unlike the case for Jupiter, the variations in wind speeds are notstrongly correlated with the positions of the belts and bands. The wind

speeds in the atmosphere of Saturn have been measured to be as

high as 1800 km/hr, which is about 4 times the highest speeds in the

atmosphere of Jupiter.

Saturns High-Velocity Winds

The surface of Saturn bears many similarities with the surface of Jupiter, but

the color contrast is generally less. This is thought to be due to Saturn being

colder than Jupiter (further from the Sun, but also smaller with less internalheat), so it has different chemical reactions in its atmosphere, leading to

different coloration.

There are large anticyclonic cells on the surface, apparently driven by the

planet's internal heat source, but none are as large as the Great Red Spot on

Jupiter, and they are not as abundant as on Jupiter.

Saturns Surface


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Cassini-Huygens1997 launch2004 Saturn arrival

The Cassini Orbiter's mission consists of delivering a probe (called Huygens,

provided by ESA) to Titan, and then remaining in orbit around Saturn for detailed

studies of the planet and its rings and satellites.


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JPL technicians reposition

and level the Cassini orbiter

in the Payload Hazardous

Servicing Facility at the

Kennedy Space Center in

July 1997, after stacking the

craft's upper equipment

module on the propulsion

module.


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The international Cassini-

Huygens mission

successfully entered orbitaround Saturn at 9:12 p.m.

PDT on June 30, 2004. This

begins a four-year study of

the giant planet, its majesticrings and 34 known moons.

Cassini-Huygens

at Saturn


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Cassini will make 74 unique orbits around the planet, using close

flybys of Saturn's largest moon Titan for gravity assists and science

data acquistion. Because of the size of Titan, the flybys will allow for

major changes in orbital paths, allowing engineers to minimize fuel use

while maximizing science data collection.

Highlights of the Saturn Tour

74 Orbits of Saturn

44 Close flybys of Titan

8 close "targeted" flybys of other satellites:3 close flybys of Enceladus

Phoebe

Hyperion

Dione

Rhea

Iapetus

30 additional satellite flybys at distances less than 100,000 kilometers

(about 62,100 miles)

Many Saturn and Ring occultation opportunities

One "Titan 180 degree" transfer

One high inclination sequence

Titan


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This false-colour composite was created with images taken during the

NASA/ESA/ASI Cassini spacecraft's closest fly-by of Titan on 16April 2005.

Titan

Titan


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This mosaic of three frames provides unprecedented detail of the high ridge area

including the flow down into a major river channel from different sources.

Titan


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Nine days before it entered orbit,

Cassini spacecraft captured thisexquisite natural color view of

Saturn's rings.

The brightest part of the rings,

curving from the upper right to

the lower left in the image, is theB ring.

Saturns Rings

Saturn's rings are made

primarily of water ice. Since

pure water ice is white, it isbelieved that different colors

in the rings reflect different

amounts of contamination by

other materials such as rock

or carbon compounds.

S t S th P l


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These images of Saturn's south pole, taken by two different instruments on Cassini,

show the hurricane-like storm swirling there and features in the clouds at various

depths surrounding the pole. Different wavelengths reveal the height of the clouds,

which span tens of kilometers in altitude.

Saturns South Pole


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Tethys is on the far side of the rings in this view; Dione and Pandora are much

nearer to the Cassini spacecraft. Dione is 1,126 kilometers (700 miles) across.

Tethys is 1,071 kilometers (665 miles) across and Pandora is 84 kilometers (52

miles) across.

Dione, Tethys and Pandora

A 330-kilometer-wide (205 mile)

impact basin can be seen near the

bottom right on Dione (at left).

Ithaca Chasma and the region

imaged during the Cassinispacecraft's Sept. 24, 2005, flyby

can be seen on Tethys (middle).


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Tethys Close-up


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Hyperion


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Rhea

Saturn's moon Rhea is an alien ice world, but its cratered surface looks in some ways similar to our

own Moon, or the planet Mercury. Rhea's icy exterior would quickly melt if this moon were brought

as close to the Sun as Mercury. Rhea is 1,528 kilometers (949 miles) across.

E l d


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Saturn's moon Enceladus is only 505 kilometers (314 miles) across, small

enough to fit within the length of the United Kingdom, as illustrated here.

The intriguing icy moon also could fit comfortably within the states ofArizona or Colorado.

Enceladus


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Uranus is the 3rd of the Gas Giant planets, and the first

planet discovered in "modern" times (1781).

It is barely visible from the Earth without a telescope, which

explains why it was not known as a planet to the ancients,

and why it had been observed various times after the

telescope had been invented without the observers realizing

that it was a planet and not a star.

Documented sightings go back to at least 1690 when

Flamsteed catalogued it as a star.

Uranus

Uranus Facts


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Discoverer: Sir William Hershel (1781)

Spacecraft Encounter(s): Voyager 2 (1986)

Mean distance from Sun: 19.19 AU (2.871 billion km/1.784 billion mi)

Length of year: 84.01 Earth years

Rotation period: 17.24 hours

Mean orbital velocity: 6.81 km/s (4.2 m/s)Inclination of axis: 97.92

Diameter: 51,118 km

Number of Observed

Satellites:>20

Diameter: 4.0 x Earth's

Mean Distance from Sun: 19.2 x Earth's

Mass: 14.5 x Earth's

Density: 0.22 x Earth's

Uranus Facts

The picture on the right uses false colors and

contrast enhancement to bring out subtle detailsin the polar region of Uranus.


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Uranus has a relatively featureless

appearance at visible wavelengths.

Even from Voyager 2 at a distance of

80,000 km there were few

distinguishable features.

This is believed to be due to Uranus

being further from the Sun than Jupiter

and Saturn, which means its

temperature is lower (only 58 degreesKelvin in the upper atmosphere).

This decreases the likelihood of

chemical reactions making the colorful

compounds that give the surface

features on Jupiter and Saturn.

In addition, the upper atmosphere is

thought to have a high-level

petrochemical haze that obscures

features lower in the atmosphere.

Uranus

Neptune is the outermost of the four


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Neptune is the outermost of the four

gas giants

Because of its distance from the Sun,

Neptune's atmosphere is a frigid -225

C (-373 F)

Neptune, like Jupiter and Saturn but

unlike Uranus, has an internal heat

source and produces 2.7 times more

heat than it absorbs.

The blue-green color of the planet is

due to the presence of methane in the

atmosphere. The atmosphere consists

mostly of hydrogen, helium and

methane.

Until the Voyager encounter in 1989,

the rings surrounding Neptune were

thought to be arcs. We now know that

the rings completely circle the planet,

but the thickness of each ring varies

along its length.

Neptune Facts


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Neptune FactsDiscoverer(s): Galle, Challis, Adams, & Le

Verrier (1846)

SpacecraftEncounter(s):

Voyager 2

Mean Distance from

the Sun:

30.06 AU (4.497 billion

km/2.794 billion mi)

Length of year: 165 years

Rotation period: 16.11 hours

Mean orbital

velocity:

5.43 km/s (3.3 mi/s)

Diameter: 49,528 km/30,775 mi

Inclination of axis: 29.6

Number of observed

satellites:

8

Comparisons with Earth:

Diameter: 3.883 x Earth's

Average distance

from Sun:

30.06 x Earth's

Mass: 17.14 x Earth's

Density: 0.31 x Earth's


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Neptune has a great storm

in the southern hemisphere

called the Great Dark Spot"

that is about half the size of

Jupiter's Great Red Spot and

so is roughly the same

diameter as the Earth, and

at least one other smaller

storm spot has been

detected as well.

Like the other gas giants,

there are rapid winds

confined to bands of latitude,

including one band that is

moving the Great Dark Spot

westward at over 1,100 km(or 700 miles) per hour.

Indeed, Neptune has the

fastest planetary winds in

the Solar System, reaching

as fast as 2,000 km (over

1 200 il ) h

Neptunes Great Dark Spot

15.Giant Planets

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