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By the Light of Jupiter’s and
Saturn’s Moons
Presented by
Professor Harold Geller
Department of Physics and Astronomy
George Mason University
What I’m Going to Talk About
• Moons of Jupiter and Saturn
–
–
–
–
–
–
–
–
–
mass
diameter
distance from sun
chemical constituents
formation
atmosphere
inner layers
rings
moons
The Moons of Jupiter
• Largest Moons
– discovered by
Galileo
• hurt geocentric view
of universe
– Io, Europa,
Ganymede and
Callisto
Where Are They?
Moon
=====
Metis
...
Io
Europa
Ganymede
Callisto
…
Sinope
Distance (km)
==========
128,000
Distance (JD) Period (days)
========= =========
1.79
0.29
421,600
671,000
1,070,000
1,880,000
5.90
9.38
15.0
26.3
1.77
3.55
7.15
16.7
23,700,000
332
758 (retro)
Io – first volcanic eruption observed
off surface of Earth
• Diameter
– 3640 km
• Mean density
– 3.5 g/cm3
• Orbital Period
– 1.77 days
• Mass
– 1.22 times Earth’s Moon
Europa
• Diameter
– 3130 km
• Mean density
– 3.0 g/cm3
• Orbital Period
– 3.55 days
• Mass
– 0.65 times Earth’s Moon
Ganymede
• Diameter
– 5270 km
• Mean density
– 1.9 g/cm3
• Orbital Period
– 7.15 days
• Mass
– 2.02 times Earth’s Moon
Callisto
• Diameter
– 4800 km
• Mean density
– 1.9 g/cm3
• Orbital Period
– 16.7 days
• Mass
– 1.46 times Earth’s Moon
Io Close Up
•First discovered
erupting volcano not
on Earth
•discovered by
Voyager (1979)
Io’s New Look
• Considered youngest surface in the Solar System
– surface is completely redone about every
million years
• Surface is continuously eroded by
– bombardment of charged particles trapped in
Jupiter's magnetic field
– And volcanic eruptions
Io’s Geo
• What is power source of geologic activity?
– tidal effect of Jupiter and Europa on Io
• Tidal forces are very large
– surface is pulled up and down hundreds of meters in
each rotation
• Is there a simple analogy?
– bending a paper clip
• it heats it
• tidal distortions keep much of Io’s interior in molten state
Io’s Geology Summary
• Io has a thin crust (primarily of sulfur)
– sitting on a molten interior
• Molten interior breaks through surface
– produces volcanoes
Io’s Magnetic Personality
• Io orbits within Jupiter’s magnetic field
– material ejected from its surface by volcanoes
(and by the charged particle bombardment from
the material already trapped in Jupiter's
magnetic field)
• primary source of the charged particles in the Jovian
magnetic field
• particles (primarily sulfur and oxygen) have a high
concentration in a doughnut shaped region
surrounding Io's orbit - Io Torus
Io’s Lightening
• Io moves within magnetic field of Jupiter
and through plasma torus
– generates electrical current
• a cylinder between Io and Jupiter of highly
concentrated magnetic flux - Io Flux Tube
• Flux Tube
– power output of about 2 trillion (2 x 1012) Watts
• comparable to TOTAL power produced on Earth
– responsible for bursts of radio
– frequency radiation long detected on Earth
Rings and Things
• A view of the ring systems
– And the significance of the ROCHE LIMIT
Europa
• Significance due to
frozen tundra
– Is it liquid or solid
beneath?
Europa’s cracks and ice rafts may indicate a
subsurface layer of liquid water
Europa’s Surface
Europa’s Surface
Europa’s Surface
Comparing Jupiter’s Moons
Saturn’s Titan
• Dense nitrogen
atmosphere
• Hydrocarbons
produced by the
interaction of sunlight
and methane
• An aerosol layer
• Possible lakes of
ethane
Near-IR HST Images
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