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Jupiter's
Moons from Earth
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Galileo saw first
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dots moving back and forth
every ~2--17 days
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deduced they were orbiting
Jupiter
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analogy to Solar System
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Modern telescopes can see
light and dark patches
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synchronous rotation about
Jupiter
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verified with spacecraft
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Ratio of orbital periods:
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Io:Europa:Ganymede [:Callisto]
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1:2:4 [:9.434]
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Tidal forces with Jupiter
and each other are important to Io, Europa, Ganymede
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As big or bigger than our
our Moon/Mercury
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Observing slight orbital
deflections (and spacecraft deflections) gives masses
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Observing occultations (and
spacecraft pictures) gives sizes
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Average densities (mass/volume)
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Io, Europa >3000 kg/m3
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Ganymede, Callisto < 2000
kg/m3
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Note Titan orbits Saturn,
Triton orbits Neptune
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