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Jupiter and the Jovian Planets
Formation of Jovian Planets
• Step 1  Accretion of planetesimals to
form large Earth-like solid planet cores of
rocks, iron, nickel
• Masses of Cores in terms of Earth’s
mass
Jupiter
28
Saturn
17
Uranus
3.5
Neptune 4.3
• Step 2  Lighter gases condense on to
the planet cores due to gravity and cold
temperatures
Jupiter – Formation of Planetary
Systems
Jupiter – “A Failed Star”
• Jupiter is 318 times more massive than the Earth;
yet, it is 80 times too small to become a star, i.e.
make nuclear energy from fusion like the Sun
• But Jupiter (and Saturn) emits roughly twice the
energy it receives from the Sun
• Energy derives from self-gravity  gravitational
compression of the interior (Jupiter shrinks about
an inch per century)
• Surface T = 124 K, but expected 109 K
(assuming Sun to be the only source)
• Jupiter radiates (124 / 109)4 = 1.7 times more
energy than would be expected
Jupiter Interior
Molecular
Hydrogen
Metallic
Hydrogen
“Ice”
Rock
Conditions inside Jupiter
• Composition like the Sun: mostly H, He
• Atmosphere 500 miles thick, largely H2, He, and
CH4, NH3, H2O
• Very low mean density of 1.33 g/cc (including
compressed core)  planet must be largely liquid
• “Surface” is largely top of liquid hydrogen ocean
(Jovian planets have no solid surface), where “Air
pressure” is 500 x Earth’s, and temperature of 4000
F
• Equator and poles do not rotate at same rate (oblate
shape): 9h 50min and 9h 55 min respectively
• Huge magnetic field, why?
Jupiter’s Interior
• Most of Jupiter is about 40,000 mile deep
ocean of liquid hydrogen
• But it is mostly metallic H2: high density
and pressure compress the H2 molecule
so that they “share” electrons, i.e.
electrons can move around like in a metal
 conduct electricity
• “Core” is solid ice, rock, iron, nickel at
very high pressure (1 billion lbs / sq. inch)
- core itself is about 28 x Earth’s mass
- temperature 50,000 F
Saturn Interior
Molecular
Hydrogen
Metallic
Hydrogen
“Ice”
Rock
Interiors of Jupiter and Saturn
Interiors of Uranus & Neptune
Molecular
Hydrogen
Rocky
Cores
Slushy
“Ice”Mantles
Uranus
Neptune
Jupiter
Saturn
Metallic
Hydrogen
Uranus
Neptune
Earth
Jupiter and Saturn have metallic hydrogen mantle; Uranus and Neptune don’t
Temperature (pressure) in Jupiter rises
faster than in Saturn with depth
Although T and P are high in the cores, not sufficient for nuclear fusion like stars
Require millions of degrees!
Jupiter – The King of Planets
Stripes,
What are they?
The Red Spot – What is it?
First seen by Galileo, over 350 years ago ! Twice the size of the Earth
A long lasting (over 300 years!!),
internally powered, cyclonic storm
(but what sustains it?)
Rapid rotation of Jupiter
Period ~ 10 hrs  In spite of its size (318 times more massive than the
Earth) it rotates 2 ½ times faster. But there is very little tilt of rotation axis
(3 degrees)  No Seasons !
Internal energy source 
Strong convection currents
What provides the internal energy source ? Self-gravity!
Jupiter – Vital Statistics
• Equatorial radius = 71,500 Kms
• Orbital period = 11.86 Earth years
• Mean density = 1.33 g/cc (3.5 times lower
than Earth’s)
• Indicates mostly H2 interior, but at
tremendous pressure  Metallic Hydrogen
(conducts electricity!), up to about 20,000
Kms into the center
• Alternating lighter and darker stripes on the
surface are zones of rising (warmer) and falling
(cooler) material
Vertical Convection: “Belts” and
“Zones”
Cloud patterns are at different temperatures (altitudes) and wind speeds;
tremendous “wind shear” (reverse direction at different altitudes)
Jovian Interior
Mostly metallic hydrogen  electrically conducting interior  huge magnetic field
Jovian Magnetosphere
Note that scale on bottom right! Jupiter’s magnetic field is 20,000 times
stronger than Earth’s
Jupiter’s Magnetic Field
• 20,000 times stronger than Earth’s, due to
convection in liquid metallic H2 interior;
convection is due to rapid rotation
• “Fast electrons” produced when the solar
wind hits Jupiter’s magnetosphere
• Lethal rays: density of particles is thousands of
times fatal human dosage
• Magnetosphere extends up to Saturn, 5 AU
away
Jupiter and the 4 Galilean Moons:
Io, Europa, Ganymede, Callisto
Relative sizes of Galilean Moons
Galilean Moons: Io, Europa,
Ganymede, Callisto Rocky to Icy
(Ganymede is the largest moon in the solar system)
Io and Europa are mostly rocky but Ganymede and Callisto have more ices;
Densities: 3.6, 3.0, 1.9, 1.8 g/cc respectively.
Jovian Moons
• In addition to the 4 Galilean satellites, 12 other
moons of Jupiter have been discovered
• Owing to Jupiter’s tidal effects all Galilean
moons are ‘synchronous rotators’: they keep
the same face towards Jupiter
• Voyager also found a ring around Jupiter, in
between two small moons before Io
• Latest NASA probe of Jupiter is called Galileo
IO
• Closest large moon to Jupiter
• Orbital period = 42 hrs
• Surface has no impact craters, so less than 1
million years old
• Many volcanic craters – active volcanoes
• No water (too hot), but lots of sulfur on surface
(sulfur condenses easily; appears black when
heated)
Erupting volcanoes (taped live!)
Hot-spots at volcanoes
Io’s Volcanic Activity
• Eight volcanoes seen by Voyager (many
more seen since)
• Plumes rise 100 miles, spread over
hundreds of miles
• Surface temp roughly 700 F near
volcanoes, -250 F away from them
• Caused by Jupiter’s tidal effect  large
land tides, up to 100 yards in height
• Friction inside Io produces heat and
volcanic activity (“squeezed” like a
ketchup bottle !)
Pizza?
Volcanic features on Io
Typical volcanic feature on Io
Io’s orbit around Jupiter:
Sulfur emission (spectral lines)
Io and Jupiter’s Magnetic Field
• Magnetic field rotates with the planet, and
electrifies the orbit of IO  plasma
(charged particles) torus surrounding orbit
of IO; contains Sulfur ions S+ (emission
spectral lines detected on the Earth)
Electrically charged atmosphere
surrounding Jupiter and orbit of Io
Radio emission from around Jupiter
- “Synchrotron radiation” at radio wavelengths is produced by “fast electrons”
from the magnetosphere
- Jupiter’s radio signals are detected on the earth! Interfere with radio
Communications with CB, short-wave radio, radar, UHF TV, etc.
Europa: Ice rafts moving on
liquid water oceans
Very thin Oxygen atmosphere has been detected on Europa
Comparison of Jovian Moons:
Evolution due to Jupiter’s gravity
Resolution
Rocky  Icy
Sizes and Distances of Galilean
Satellites
Sizes relative to Earth’s Moon ( = 1): 1.1, 0.9, 1.5, 1.4 respectively
Many moons of Jupiter