Chapter 11: Jupiter Giant of the Solar System

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Chapter 11 JupiterGiant of the Solar System

• Differences from terrestrial planets
• Atmosphere
• Structure and Composition
• Magnetosphere
• Satellites

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After completing this chapter, you should be able
to

• compare the general physical properties of
  Jupiter/Earth.
• compare orbital and rotational properties of
  Jupiter/Earth.
• describe atmosphere, hydrosphere, lithosphere,
  magnetosphere, and biosphere of Jupiter and
  compare to Earth.
• describe Jupiter's cycle of visibility as seen
  from Earth.
• explain why Jupiter's atmosphere is
  so different from
  Earth's.
• describe Jupiter's ring system.
• describe physical properties/origin of Galilean
  satellites.
• explain the origin of Io's volcanoes, Europas
  surface.

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Jupiter, Saturn, Uranus, NeptuneThe Jovian
Planets

• Outer or giant or jovian planets.
• Over 1400 Earths could fit inside Jupiter
• Composed primarily of lighter ices, liquids,
  gases.
• Do not have solid surfaces more like vast,
  ball-shaped oceans with much smaller, dense cores
  at their centers.
• Extensive satellite and ring systems.

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Planet PropertiesRelative Mass of Planets
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Planet PropertiesAverage Distance from Sun
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Planet PropertiesPlanetary Densities
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Chemistry of Giant Planets

• Jupiter Saturn nearly same chemical makeup as
  Sun.
• primarily hydrogen and helium
• by mass 75 hydrogen, 25 helium
• Gas compressed in interior until hydrogen
  liquifies.
• Uranus and Neptune are smaller, attracted
  less hydrogen and helium.
• All have interior core composed of rock, metal,
  and ice approximately 10 x mass of Earth.
• Chemistry dominated by hydrogen, oxygen in
  form of H2O (water and water ice)
• Reducing chemistry
• Atmospheres hydrogen-based gases CH4
  (methane) or NH3 (ammonia) or more complex

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Jupiter Fact Sheet

• Diameter 142,800 km (88,736 miles, 11.2 x
  Earth, 1/10 x Sun)
• Mass 318 x Earth (1/1000 x Sun)
• Density 1.33 g/cm3 (H2O1, Earth 5.5)
• Length of Day 9 hrs 55 min
• Length of year 12 Earth years
• Average Distance from Sun 5.2 AU (483
  million miles)
• Tilt of Axis 3.1o
• Escape Velocity 60 km/s
• Distance across the Great Red Spot
  40,000 km (2xEarths diameter)
• Temperature at Cloud Tops 124 K
• Temperature at core 20,000 K
• Rings 1, very thin
• Satellites 28 known

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Two Object Solar System?

• The Sun and Jupiter.
• Jupiter has more mass than all of the other
  objects in solar system combined.
• Its gravity
• moves comets into new orbits,
• helps keep asteroids in place,
• may have created the Oort Cloud of comets,
• controls a system of 28 moons
• Its tidal pull has
• kept Io molten for billions of years
• probably provided Europa with a deep, liquid
  ocean
• Its atmosphere has
• storm swirls larger than the entire Earth
• winds that move at over 400 km/hr faster than
  interior

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View from Earth

• Closest of Jovian planets to Earth
  ( 4AU at its nearest).
• Fourth brightest object
• brightest when
  near
  opposition
• up to 50 across
• Earth-based telescopes
• distinct, multi-colored bands across surface
  large reddish area in southern hemisphere
• satellites
• intense bursts of radio energy

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Viewing Jupiter

• Oppositions occur every 399 days, so Jupiter is
  nearest the Earth and brightest once each year.
• Because of its great distance from the Earth, its
  brightness does not vary greatly.
• It moves eastward through approximately one
  constellation of the zodiac each year, because it
  takes just under 12 years to orbit the Sun.
• Jupiter's four large moons (Galilean satellites)
  are easily visible through a small telescope
  and even binoculars.
• The changing positions of these moons can be seen
  during one night's observations.

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Rotation Rate

• No solid surface features to observe.
• Cloud features in upper atmosphere move at
  different rates, depending on latitude, activity.
• Near equator 9 hr 50 m period
• Closer to poles 9 hr 55 m period (globe)
• Magnetosphere-related radiation
• 9 hr 55 m period
• Observed flattening too small for planet composed
  entirely of hydrogen and helium.

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Questions

• How do observations of magnetosphere allow
  astronomers to measure the rotation rate of a
  planets interior?
• What is differential rotation? How is it
  observed on Jupiter?
• What does Jupiters degree of flattening tell us
  about its interior?

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View from Space

• Pioneer 10 and Pioneer 11 (launched 1972, 1973)
  were first spacecraft to visit outer
  planets.
• navigate asteroid belt
• study charged particles and magnetic field
• photograph surface
• Voyager 1 and Voyager 2 launched in 1977.
• Designed to study Jupiter and Saturn both still
  transmitting data as they travel toward boundary
  of solar system and into interstellar space.
• Voyager 2 passed
• within 80,000 km of Uranus
  (within 16 km of planned
  target) and
• 5000 km above Neptunes clouds.
• Galileo launched in 1989 arrived December, 1995.

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Voyager Missions Path through the Solar System
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Jupiter Highlights of Voyager Mission

• Found 3 new satellites.
• Io - active volcanism.
• Discovered zones of aurora.
• Discovered rings.

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Galileo ProjectThe Moon, Asteroids, Jupiter, Io,
and Europa

• Launched in 1989 from space shuttle Atlantis.
• Orbiter and atmospheric probe

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Galileo Highlights

• Discovery of an intense new radiation belt
  approximately 50,000 km (31,000 miles) above
  Jupiter's cloud tops.
• Jovian wind speeds in excess of 600 km/hr (gt 400
  mph) 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 than anticipated
  (about 10 of that found in an equal area on
  Earth). 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 of Io's surface due to
  continuing volcanic activity since the Voyagers
  flew by in 1979.
• Preliminary data support the tentative
  identification of intrinsic magnetic fields for
  both Io and Ganymede.
• Evidence for liquid water ocean under Europa's
  surface.

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Cassinis View of Jupiter

• Jupiter in three wavelengths
• left blue (visible)
• middle ultraviolet
• right infrared

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Interior Structure

• A rough model of Jupiter's internal structure can
  be deduced from the planet's mass, density,
  rotation, and shape.
• Jupiter appears to be highly differentiated with
  a relatively small rocky and/or metallic core,
  perhaps the size of Earth and
  with 10 x Earths mass.

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Jupiters Internal Structure
Structural Components of total planetary radius Scaled 1 meter radius of Jupiter
Cloud layers in upper atmosphere 0.1 99.9 100 cm
Gaseous atmosphere 7 93 100 cm
Hydrogen in liquid form 22 71 93 cm
Hydrogen in liquid metal form 57 14 71 cm
Rocky, high density core 14 0 14 cm
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Jupiters Interior
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Jupiter Composition

• Interior composition
• mostly simple molecules of hydrogen, liquid form.
  
• Under the cloud layers, as the
  pressure increases, the hydrogen
  changes to liquid hydrogen.
• Further increases in pressure change liquid
  hydrogen to liquid metallic hydrogen.
• Core composition heavier, rocky and
  metal elements.

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Jupiters Heat Engine

infrared wavelengths
visible wavelengths
Atmospheric motions appear to be driven by
internal and external heating.
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Jupiter Heat Sources

• Atmospheric motions driven by internal and
  external heating.
• External
• Solar energy
• Internal
• Primordial heat
  generated during
  formation by collapse of materials onto core.
• Contraction slow
  shrinking of planet after formation
• Jupiter radiates about 1.6 times as much
  energy into space as it receives
  from the Sun.

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Jupiters Internal Motions

• The drawing illustrates a kind of global motion
  typical of motions in both the atmosphere and the
  interior of a planet.
• Material rises from warmest region, and moves in
  a roiling motion (like boiling of a pot).
• Shown are three different cells of activity in
  the atmosphere where the air turns over (depicted
  by red sheets).
• In the interior of Jupiter, the liquid
  layers are warm enough to move in this fashion.

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More on Interior Motions
The drawing shows layered cylinders of material,
in motion, rolling in different directions. This
pattern may be in operation with the tips of
cylinders corresponding to the striped pattern of
clouds seen in the atmosphere.
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Questions Internal Structure

• What is thought to lie beneath Jupiters clouds?
  
• Why do we think this?
• Explain a theory that accounts for the
  unexpectedly high temperatures observed at
  Jupiters cloud tops.

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Atmosphere
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Atmosphere Composition

• Jupiter has an extremely dense atmosphere.
• Its composition is more like the Sun
  than any of the terrestrial
  planets.
• Hydrogen - 86.
• Helium - 13.
• Methane (CH4) - trace.
• Ammonia (NH3) - trace.
• Water (H2O) - trace.
• Believed that the bulk of the interior has
  similar composition.
• This property makes it quite different than the
  terrestrial planets and explains its relatively
  low bulk density.

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Jupiters Cloud Patterns

• Pattern of clouds in white, brown, and orange.
• Other shapes include eddy shapes, white ovals,
  brown ovals, and brown barges.
• Eddies and white ovals are outlined in this
  picture.
• Form in stripes and move across face of Jupiter.
• Stripes similar to those found on all the giant
  planets.

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Cloud Layers of Jupiter

• Three different layers of clouds or clouddecks.
• Composition of clouddecks.
• 1st ammonia.
• 2nd ammonium hydrosulfide
  (ammonia sulfur)
• 3rd ordinary water clouds

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Atmosphere Circulation

• Rapid rotation rate causes planet's atmosphere to
  
• bulge at the equator and
• be flattened at the poles.
• Rotation rate is greater at the equator than
  at the poles (differential
  rotation).
• Jupiter's rapid rotation deflects rising and
  sinking currents of gases (Coriolis effect) into
  strong zonal flows of winds
  moving east and west.
• somewhat like super jet streams on Earth.
• The dark belts are bands of sinking, cooler
  gases, and the light zones are bands of rising,
  warmer gases.
• Equivalent to Earths high and low pressure
  systems.

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Global Circulation

• Circulation of the Jovian atmosphere. The global
  circulation pattern shown here indicates the
  location and designations of the belts and zones
  in Jupiter's cloud layer. (NASA)

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Belts and Zones

• Motions in the Jovian atmosphere. These drawings
  indicate both the horizontal (left) and vertical
  (right) circulation in the clouds of Jupiter.
  (NASA)

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Belts and Zones

• Wind flow patterns in Jupiters belts and zones

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Atmosphere Colors

• Colors are caused by trace amounts of organic,
  sulfur, and/or hydrogen molecules which absorb
  sunlight at different wavelengths.
• A great deal of turbulence occurs at the
  interface between belts and zones.
• These are regions of large jovian storms.

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Storms The Great Red Spot
The Great Red Spot is thought to be a hurricane
which has been raging on Jupiter for well over
300 years. High-pressure region with high, cold
cloud tops (CCW rotation).
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Great Red Spot
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Great Red Spot
HST images of Great Red Spot over a seven year
period.
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Storms White Ovals
Collections of white clouds, grouped together
into an oval shape commonly found in all regions
of Jupiters atmosphere.
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White Spots vs. GRS

• High pressure storms.
• Compared to Great Red Spot (GRS)
• Lower in the atmosphere than GRS.
• Smaller than GRS.
• Do not last as long as GRS.

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Storms Brown Barges

• Low pressure storms.
• Lowest in the atmosphere.
• actually holes in atmosphere
• Appear around 20oN latitude.
• Short-lived compared to GRS

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Atmosphere Origin and Evolution

• Jupiter's atmosphere is thought to be a remnant
  of Solar System formation.
• Evolved very little since initial formation.
• That is why planetary scientists feel it is
  extremely important to study it.
• It may be somewhat similar to
  Earth's primary atmosphere.

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Questions Atmosphere

• Why has Jupiter retained most of its original
  atmosphere?
• List some similarities and differences between
  Jupiters belts, zones, and spots and weather
  systems on Earth.
• What is the Great Red Spot?
• What is the cause of the colors in Jupiters
  atmosphere?

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Magnetosphere

• Jupiter has an extensive magnetosphere about 10
  time stronger than the Earth's.
• This strong magnetic field is probably caused by
  Jupiter's very rapid rotation and its
  considerable liquid metallic hydrogen core.
• Its magnetic field extends far out into space in
  a sheet structure centered on the plant's
  equator.
• Jupiter has extremely powerful (and deadly)
  radiation belts circling the planet. They are
  much more forceful than Earth's.

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Jupiters Magnetosphere

• Jupiter's magnetosphere is biggest thing in
  entire solar system.
• Big enough to hold all of Jupiter's moons or Sun
  itself.
• Tail extends to Saturn.
• From Earth, would appear as large as the full
  moon.
• High levels of energetic particles trapped in
  regions of magnetosphere, similar to Earths Van
  Allen radiation belts.
• New region found by Galileo in uppermost
  atmosphere 10 x Van Allen in
  strength.
• Donut-shaped cloud inside the magnetosphere
  coincides with Io.
• Jupiter lights up with very beautiful aurora.
  Jupiter also makes radio signals and other waves
  (whistler waves, chorus and hiss).

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Jupiters Magnetosphere
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Model of Jupiters Magnetosphere

• Model of magnetosphere showing interaction with
  solar wind and Io torus.

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The Io Torus
The Io plasma torus is the result of material
being ejected from Io's volcanoes and swept up by
Jupiter's rapidly rotating magnetic field.
Spectroscopic analysis indicates that the torus
is composed primarily of sodium and sulfur atoms.
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The Io Torus
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Jupiters Aurora

• Very powerful energy source. Produces much more
  power (1,000,000 MWatts) than the Earth's aurora
  (1000 MWatts).
• For comparison, a large city uses about 10,000
  MWatts.
• Significantly impacts atmosphere.
• Unlike the Earth, the Jovian aurora is thought to
  come from two places
• from the moon Io, and
• from currents carrying particles from somewhere
  deeper in Jupiter's magnetotail.

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Aurora
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Jupiter in Radio Wavelengths

• View of radio wavelength radiation from particles
  trapped in Jupiters magnetic field.

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Questions Magnetosphere

• What is responsible for Jupiters enormous
  magnetic field? Why is it so much larger than
  Earths?
• How was Jupiters magnetic field discovered?
• Compare Jupiters magnetic field to Earths
  magnetic field.
• Include generation, field strength, aurora,
  trapped particles, interaction with moons.

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Hydrosphere

• Near the top of Jupiter's atmosphere, water is
  frozen, but below the cloud tops the temperature
  and pressure gradually change increase.
• There is probably a level at which liquid water
  is stable.
• There should be a fair amount of water in the
  jovian atmosphere.
• Results from the Galileo atmospheric probe
  indicated less water than predicted. These
  results are still being analyzed.

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Biosphere

• Of course, none is known, but some have
  speculated about the possibility of life existing
  at hospitable levels in the jovian atmosphere.
• However, strong down drafts are likely to destroy
  fragile organic compounds soon after they form.

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Jupiters Moons
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Transits of Jupiters Moons
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The Moons of Jupiter

• 28 known moons
• 4 very small moons orbiting lt 3.1 x
  radius of Jupiter
• 4 large Galilean moons
• 8 small moons
• 4 in eccentric, inclined orbits,
  11 million km from Jupiter
• 4 in eccentric, retrograde orbits,
  22 million km from Jupiter
• 12 recently discovered small moons in inclined,
  eccentric, mainly retrograde orbits, 10-25
  million km from Jupiter

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Jupiters Moons

• Jupiter has 28 known moons.
• Most are rather small, but the four largest
  (discovered by Galileo in 1609) are as large or
  larger than the Earth's Moon.
• The largest (Ganymede) is larger than the planets
  Mercury and Pluto.
• The comparative features of the Galilean Moons
  mimic to some extent the properties of the
  planets in the Solar System.
• The jovian satellite system is itself somewhat
  like a miniature solar system.

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Jupiters Galilean Satellites

• Io, Europa, Ganymede, Callisto comparable in size
  to Earths Moon, move in nearly circular orbits
  about Jupiter.
• System similar to scaled-down solar system,
• as distance from Jupiter increases, moons sizes
  increase and moons densities decrease,
• Jupiters rotation slowing due to tidal drag of
  Galilean satellites, and satellites orbits
  slowly increasing.
• Io, Europa, and Gandymede locked in a 124
  orbital resonance Callisto approaching 2x period
  of Gandymede. (1248)

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The Galilean Satellites
These are the four moons discovered by Galileo,
shown in correct relative size. Ganymede is the
largest satellite in the solar system.. (NASA)
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Galilean Moons
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Galilean Moon Facts
Distance from Jupiter (km) Diameter (km) Orbital period (days)
Io 422,000 3640 1.77
Europa 671,000 3130 3.55
Ganymede 1,070,000 5270 7.15
Callissto 1,880,000 4800 16.7
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Galilean Moons in Cross-Section
Core Mantle Crust
Io Iron/iron sulfide Rocky Young, thin, volcanic
Europa Iron/iron sulfide Rocky Thin?, water/ice
Ganymede Iron/iron sulfide Rocky Thick, icy
Callisto Ice/rock
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Io
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Io
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Io

• Innermost Galilean satellite.
• Composition is mostly rocky, almost no
  volatiles.
• Driest place in the outer Solar System.
• No impact craters, surface renewed to 300 feet
  every million years.
• Surface composition is sulfur lava and SO2.
• Active volcanoes erupting sulfur, SO2, and sodium
  compounds.
• Extremely violent eruptions are 10 x greater than
  Earth's.
• Volcanoes eject matter into Jupiter's magnetic
  field and radiation belts (10,000 tons/second).

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Volcanic Activity on Io

• Source of geological activity on Io is tidal
  effect of Jupiter on Io as it orbits the giant
  planet.
• These tidal forces are so large that Io's surface
  is pulled upwards and downwards by hundreds of
  meters in each rotation.
• Tidal squeezing causes the interior to melt,
  causing volcanic activity.
• Heat flow is 30 times greater than Earth's.
• A very thin (10-7 Earth's) atmosphere of SO2.

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Volcanic Vents on Io
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Recent Volcanic Activity on Io
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Io Torus

• The following series of photographs, taken
  through a ground-based telescope on Earth, shows
  the cloud of sodium atoms surrounding Io as it
  orbits Jupiter.
• The yellow color of the cloud is due to the fact
  that sodium atoms emit most strongly in a pair of
  emission lines in the yellow part of the
  spectrum.
• Once this gas, which also includes other atoms
  such as sulfur, escapes from Io, it becomes
  ionized and then is spread all the way around
  Io's orbit by magnetic forces.
• This ionized gas is not visible here, so we do
  not see the full extent of the torus.
• The sizes of Jupiter, Io (dot inside the
  cross-hair), and Io's orbit are all to correct
  relative scale.
• (B. A. Goldberg, G. W. Garneau, and S.K. LaVoie,
  JPL)

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Io Torus
Ground-based telescope on Earth, shows the cloud
of sodium atoms surrounding Io as it orbits
Jupiter. The sizes of Jupiter, Io (dot inside
the cross-hair), and Io's orbit are all to
correct relative scale. (B. A. Goldberg, G. W.
Garneau, and S.K. LaVoie, JPL)
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Three Icy Moons
Callisto Ganymede Europa
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Europa
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Europa

• Young smooth surface with very few craters.
• Perhaps an icy surface and a rocky interior.
• Cracks are observed as ridges of fresh ice on the
  surface.
• May be an ocean of liquid water below the icy
  surface.
• A thin atmosphere of oxygen was detected by
  Galileo spacecraft.

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Europas Surface A Close-up View
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(No Transcript)
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Surface of Europa

• The blue hues represent ice plains divided by
  dirty red and brown bands of terrain. The dark
  color may represent organic matter.
• The cause for many of the cracks remains unknown
  but may involve shifting stresses from gravity
  and temperature variations.

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Europas Evolution

• Europa, like Io, is heated internally by the
  tidal tug-of-war with Jupiter.
• Since Europa is further from Jupiter than Io,
  the tidal effect is less dramatic.
• In the case of Europa, the effect of the tides
  induced by Jupiter is to heat the interior of
  Europa sufficiently to keep the surface soft.
• Thus, no vertical relief features can survive for
  long on Europa's surface, explaining its smooth
  appearance.

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Europa--Surface and Interior
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Ganymede
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Ganymede

• Largest satellite in the Solar System.
• Composed of a mixture of rock and water ice.
• Probably a very thick crust of water ice.
• It has a combination of cratered and grooved
  terrain.
• Changing ice phases may have caused it to expand
  3.5 billion years ago forming grooves and ridges.

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Moon Size
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Ganymedes Features

• Largest moon in the Solar System (larger than
  Mercury).
• Largely covered by a frozen water ocean.
• Portions of surface look young geologically
  portions look old.
• Large grooves in surface crust broken into
  fragments.
• Evidence for past plate tectonic activity first
  conclusive evidence of plate tectonics in the
  Solar System beyond the Earth.

• Weak magnetic field, first detected for satellite
  in this Solar System.

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Ganymede-Surface Features
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Ganymedes Interior
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Callisto
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Callisto

• Outermost of the Galilean Satellites.
• Very old surface, covered with craters and impact
  basins.
• Lowest density of the large moons.
• Composed of perhaps 50 water ice.
• Shows the least amount of tectonic activity.
• It may have some internal differentiation caused
  by radioactive decay.

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Callistos Cratered Surface

• Callisto has the most heavily cratered surface of
  the four Galilean moons.
• The number of craters imply that the surface of
  Callisto is 4 billion years
  old.

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Callistos Surface

• Similar in appearance to Ganymede, more craters
  and fewer fault lines.
• Most obvious feature huge series of concentric
  ridges surrounding two large basins.
• Ridges resulted from impact with asteroid or
  comet. Up-thrust ice partially melted
  resolidified quickly, before the ripples
  subsided.
• Today, ridges and rest of crust are frigid ice,
  showing no obvious signs of geological activity.
• The density of impact craters on the Valhalla
  basin indicates that it formed 4 billion years
  ago.

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Comparison of Galilean Satellites
MOON DENSITY WATER CONTENT ACTIVITY
Io highest least greatest
Europa 2nd 2nd 2nd
Ganymede 3rd 3rd 3rd
Callisto lowest most least
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Questions Moons

• Compare sizes of Galilean moons terrestrial
  objects.
• Describe the variation in density as a function
  of distance from Jupiter for the Galilean moons.
• How does the amount of cratering vary among the
  Galilean moons? Does it depend on their
  location? If so, how?
• What is the source of all the activity observed
  on Jupiters Galilean satellites?
• Why is there speculation that the Galilean moon
  Europa might be an abode for life?
• Water is relatively uncommon among the
  terrestrial planets. Is it common among the
  moons of Jupiter?

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Jupiters Ring
Discovered in 1979 by Voyager missions inside
orbit of innermost moon few 1000 km across, few
10s km thick in equatorial plane made of small
grains of rocky material, albedo 0.05, no ice.
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Questions Rings

• How was Jupiters ring discovered?
• Describe the ring
• location,
• particle size range,
• particle density,
• particle color,
• source of ring material.

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Jupiter

• Largest planet in the solar system.
• Primarily composed of hydrogen and helium.
• Rapid, differential rotation.
• Internal structure and heat source.
• Thick atmosphere with 3 main cloud layers.
• Layers arranged into bands of bright zones and
  darker belts that cross surface parallel to
  equator and are the result of convection and
  rapid planetary rotation.
• Stable zonal E-W wind flow underlying
  belts/zones.
• Long term weather patterns/storms
  Great Red Spot, white ovals, brown ovals.
• Magnetosphere
• 28 known satellites
• Galilean satellites
• Small, dark, faint rings discovered by Voyager
  1.

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Overview of Jupiter from Earth

• Jupiter is a giant planet located fifth from Sun.
• Its mass of 318 x Earths and diameter of 11
  Earth diameters yield an average density of 1.3 x
  water.
• It appears through ground-based telescopes as a
  gas giant flattened by rapid rotation, with
  reddish and whitish belts and zones. Within one
  zone in S-hemisphere is the Giant Red Spot
  (2xEarth). Many satellites visible four
  largest called Galilean satellites.
• Ground-based radio telescopes found synchrotron
  radiation, indicating the presence of a strong
  magnetic field.
• Other observations show that Jupiter emits 2x
  energy it captures from Sun. Excess energy from
  internal heat from time of Jupiters formation.

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Overview of Jupiter from Space

• Pioneer and Voyager probes show highly turbulent,
  stormy atmosphere, lightning, and aurorae.
• Confirmed expected presence of hydrogen and
  helium as the main constituents of the planet.
• Atmosphere hydrogen, helium, ammonia, methane
• Voyager discovered a ring composed of small,
  dark, rocky grains.
• Magnetosphere mapped extensive and tilted 100 to
  rotation axis.
• Interior structure modeled as a rocky core
  surrounded by a region of liquid metallic
  hydrogen. Believed that this material behaves
  like a metal and that its rotational and
  turbulent convection motions produce the planets
  magnetic field.

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Overview of Jupiters Moons

• 28 known satellites
• Four largest, called the Galilean satellites,
  form a miniature solar system around Jupiter .
• Io
• volcanic
• gases form a cloud around Io and its orbit
  creates aurora torus
• Europa
• straight-line features in icy methane and ammonia
  surface
• possible water ocean beneath surface
• Ganymede
• largest satellite in solar system, first observed
  with magnetic field.
• cratered, icy crust with evidence past plate
  tectonics activity
• Possible water ocean beneath surface
• Callisto
• old, icy, saturated with craters and a large
  multi-ringed basin