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Chapter 8 Jovian Planets. Mass : 1.9 × 10^27 kg (twice as much as all other planets put together) Radius : 71,500 km (112 times Earth's) Density : 1300 kg/m - cannot be rocky or metallic as inner planets are

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orbital and physical properties

Mass: 1.9 × 10^27 kg (twice as much as all other planets put together)

  • Radius: 71,500 km (112 times Earth's)
  • Density: 1300 kg/m - cannot be rocky or metallic as inner planets are
  • Rotation rate: Problematic, as Jupiter has no solid surface; different parts of atmosphere rotate at different rates
  • From magnetic field, rotation period is 9 hr, 55 min

Orbital and Physical Properties

slide4

Atmosphere has bright zones and dark belts

  • Zones are cooler, and are higher than belts
  • Stable flow underlies zones and bands, called zonal flow
  • Simplified model:
the atmosphere of jupiter1

Composition of atmosphere: Mostly molecular hydrogen and helium; small amounts of methane, ammonia, and water vapor

These cannot account for color; probably due to complex chemical interactions

The Atmosphere of Jupiter

the atmosphere of jupiter2

No solid surface; take top of troposphere to be at 0 km

Lowest cloud layer cannot be seen by optical telescopes

Measurements by Galileo probe show high wind speeds even at great depth—probably due to heating from planet, not from Sun

The Atmosphere of Jupiter

the atmosphere of jupiter3

Great Red Spot has existed for at least 300 years, possibly much longer

Color and energy source still not understood

Lightning-like flashes have been seen; also shorter-lived rotating storms

One example: Brown Oval, really a large gap in clouds

The Atmosphere of Jupiter

internal structure

Jupiter radiates more energy than it receives from the Sun:

    • Core is still cooling off from heating during gravitational compression

Internal Structure

  • Could Jupiter have been a star?
    • It would need to be about 80 times more massive to be even a very faint star.
jupiter s magnetosphere

Jupiter is surrounded by belts of charged particles, much like the Van Allen belts but vastly larger.

Magnetosphere is 30 million km across

Intrinsic field strength is 20,000 times that of Earth

Magnetosphere can extend beyond the orbit of Saturn

Jupiter's Magnetosphere

the moons of jupiter

63 moons have now been found orbiting Jupiter, but most are very small

  • The four largest are the Galilean moons, so called because they were first observed by Galileo:
    • Io, Europa, Ganymede, Callisto
  • Galilean moons have similarities to terrestrial planets: largest is somewhat larger than Mercury, and density decreases as distance from Jupiter increases

The Moons of Jupiter

the moons of jupiter1

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

    • Many active volcanoes, some quite large
    • Can change surface features in a few weeks
    • No craters; they fill in too fast—Io has the youngest surface of any solar system object
    • Europa has no craters; surface is water ice, possibly with liquid water below

The Moons of Jupiter

the moons of jupiter2

Ganymede is the largest moon in the solar system—larger than Pluto and Mercury

History similar to Earth's Moon, but water ice instead of lunar rock

Callisto is similar to Ganymede; no evidence of plate activity

The Moons of Jupiter

saturn orbital and physical properties

Saturn Orbital and Physical Properties

Mass: 5.7 × 10^26 kg

Radius: 60,000 km

Density: 700 kg/m — less than water!

Rotation: Rapid and differential, enough to flatten Saturn considerably

Rings: Very prominent; wide but extremely thin

saturn s atmosphere

Saturn's atmosphere also shows zone and band structure, but coloration is much more subdued than Jupiter's

Mostly molecular hydrogen, helium, methane, and ammonia; helium fraction is much less than on Jupiter

Saturn's Atmosphere

saturn s atmosphere1

Similar to Jupiter's, except pressure is lower

Three cloud layers

Cloud layers are thicker than Jupiter's; see only top layer

Saturn's Atmosphere

saturn s atmosphere2

Wind patterns on Saturn are similar to those on Jupiter, with zonal flow

Jupiter-style “spots” rare on Saturn; don't form often and quickly dissipate if they do

As expected for a planet with an atmosphere, there is a vortex at Saturn's south pole.

Saturn's Atmosphere

saturn s interior and magnetosphere

Saturn also radiates more energy than it gets from the Sun, but not because of cooling:

    • Helium and hydrogen are not well mixed; helium tends to condense into droplets and then fall
    • Gravitational field compresses helium and heats it up
    • Saturn also has a strong magnetic field, but only 5% as strong as Jupiter's

Saturn's Interior and Magnetosphere

saturn s spectacular ring system

Ring particles range in size from fractions of a millimeter to tens of meters

  • Composition: Water ice—similar to snowballs
  • Why rings?
    • Too close to planet for moon to form—tidal forces would tear it apart
  • Details of formation are unknown:
    • Too active to have lasted since birth of solar system
    • Either must be continually replenished, or are the result of a catastrophic event

Saturn's Spectacular Ring System

the moons of saturn

Saturn's many moons appear to be made of water ice

  • In addition to the small moons, Saturn has:
    • Six medium-sized moons (Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus)
    • One large moon (Titan) which is almost as large as Ganymede

The Moons of Saturn

the moons of saturn1

Titan has been known for many years to have an atmosphere thicker and denser than Earth's; mostly nitrogen and argon

Makes surface impossible to see; the upper picture at right was taken from only 4000 km away

Trace chemicals in Titan's atmosphere make it chemically complex

The Moons of Saturn

the discoveries of uranus and neptune

Uranus was discovered in 1781 by William Herschel; first planet to be discovered in more than 2000 years

Little detail can be seen from Earth; arrows point to three of Uranus's moons:

The Discoveries of Uranus and Neptune

13 1 the discoveries of uranus and neptune

Neptune was discovered in 1846, after analysis of Uranus's orbit indicated its presence

Details of Neptune cannot be made out from Earth either; arrows again point to moons:

13.1 The Discoveries of Uranus and Neptune

orbital and physical properties2

Uranus

Neptune

Orbital and Physical Properties

Mass

14.5 x Earth

17.1 x Earth

Radius

4.0 x Earth

3.9 x Earth

Density

1300 kg/m^3

1600 kg/m^3

orbital and physical properties3

Peculiarity of Uranus: Axis of rotation lies almost in the plane of its orbit. Seasonal variations are extreme.

Uranus and Neptune are cold enough that ammonia freezes; methane dominates and gives the characteristic blue color

Orbital and Physical Properties

slide30

The Moon Systems of Uranus and Neptune

Uranus has 27 moons, five of which are major: Miranda, Ariel, Umbriel, Titania, and Oberon

Similar to Saturn's medium-sized moons, except that all are much less reflective

Umbriel is the darkest

the moon systems of uranus and neptune

Neptune has 13 moons, but only two can be seen from Earth: Triton and Nereid

Triton is in a retrograde orbit; Nereid’s is highly eccentric

Triton’s surface has few craters, indicating an active surface. There appear to be ice volcanoes andNitrogen geysers

The Moon Systems of Uranus and Neptune