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The Galilean Satellites

Jupiter has four planetary-sized moons first seen by Galileo and easily
visible in binoculars.
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The Galilean Satellites

Jupiter has four planetary-sized moons first seen by Galileo and easily
visible in binoculars.
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The Galilean Satellites

Jupiter has four planetary-sized moons first seen by Galileo and easily
visible in binoculars.
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Origin of the Galilean Satellites
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These large “regular” satellites of Jupiter probably formed in a
miniature version of the Solar Nebula around Jupiter as Jupiter itself
was forming.
Like the Solar System the inner Jovian moons are rocky and the outer
ones are icy.
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Origin of the Galilean Satellites

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These large “regular” satellites of Jupiter probably formed in a
miniature version of the Solar Nebula around Jupiter as Jupiter itself
was forming.
Like the Solar System the inner Jovian moons are rocky and the outer
ones are icy.
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Ganymede
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Ganymede is the Solar System's largest moon and is a bit larger than
the planet Mercury.
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Ganymede
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It has a density of 1.9 g/cm3, suggesting a rocky core and icy mantle
and exterior
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Ganymede
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It has a density of 1.9 g/cm3, suggesting a rocky core and icy mantle
and exterior.
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Ganymede
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Fresh craters expose bright ice.
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Darker = older !
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Ganymede
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Ganymede exhibits two terrains
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one is dark and heavily cratered
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the other is young and marked by parallel ridges/grooves.
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Ganymede
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Ganymede exhibits two terrains

one is dark and heavily cratered

the other is young and marked by
parallel ridges/grooves.
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Ganymede
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Ganymede exhibits two terrains

one is dark and heavily cratered

the other is young and marked by
parallel ridges/grooves.
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Crustal Movement on Ganymede
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One look at the distribution of dark terrain on Ganymede provides
convincing evidence that sections of crust have moved around.

Maybe more like arctic ice rafts than plate tectonics, but there are
many parallels.
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Callisto
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Jupiter has four planetary-sized moons first seen by Galileo and easily
visible in binoculars.
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Callisto
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The outermost Galilean moon, Callisto, is a stark contrast to
Ganymede.

Despite being a near twin in size and density it shows no signs of
surface activity.
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Callisto

The outermost Galilean moon, Callisto, is a stark contrast to
Ganymede.

There is evidence, from the gravitational deflection of spacecraft
flying by Callisto that the interior is not differentiated!! → slow
formation.
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Callisto
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Eroded craters point to
ice sublimation.
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Callisto
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Ancient big impacts
may have released
mantle slush.
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Io and Geological Activity
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Io, being similar in size to the Earth's Moon, might be expected to be a
geologically dead world.
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The Galilean Satellites

Jupiter has four planetary-sized moons first seen by Galileo and easily
visible in binoculars.
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Io and Geological Activity
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It turns out to be the most volcanically active world in the Solar
System.
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Io and Geological Activity
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It turns out to be the most
volcanically active world in
the Solar System.

No impact craters!

Coloration from Sulfur
and sulfur
compounds.
Density = 3.0 g/cm3

mostly rock

formed in a “warm
location”?

ices baked away?
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Io's “Atmosphere”
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The volcanic activity produces a continuously escaping tenuous
atmosphere of sulfur and sodium near Io, and a “torus” of this material
around Jupiter.
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Heating Io Internally – Tidal Stretching
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Io has an elliptical orbit due to tugs from the other large Galilean
satellites.
The solid body of Io experiences significant, regular tidal distortion as
a result (the orbit takes just under 2 days)
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Heating Io Internally – Tidal Stretching
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The tidal stretching heats the interior of Io significantly, so much so
that volcanism is rampant.
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Europa and Tidal Heating
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Europa is the next Galilean satellite out from Jupiter
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Craters are rare on Europa as well

tidal heating is much weaker – greater distance / slower orbit
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Europa, however has an icy surface – easier to melt.
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Europa and Tidal Heating
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Europa is the next Galilean satellite out from Jupiter
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Craters are rare on Europa as well

tidal heating is much weaker – greater distance / slower orbit

Europa, however has an icy surface – easier to melt.
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Europa and Tidal Heating
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Europa also has a density close to 3.0 g/cc.

The outer layer of ice is the top of a true frozen-over “ocean” about
100 kilometers deep.

Weak tidal heating combined with radioactive decay keep Europa
warm enough keep the ocean liquid below a few kilometers of icy
crust.

Liquid water in the outer solar system!!!
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Europa and Tidal Heating
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Europa also has a density close to 3.0 g/cc.

The outer layer of ice is the top of a true frozen-over “ocean” about
100 kilometers deep.

Weak tidal heating combined with radioactive decay keep Europa
warm enough keep the ocean liquid below a few kilometers of icy
crust.

Liquid water in the outer solar system!!!
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Europa as an Abode for Life
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Europa's ocean is likely habitable if life
formed or was delivered there.
Interestingly, it is now thought that life on
Earth may have originated near
submerged volcanic vents.
The most primitive life forms on Earth, the
extremophiles, thrive in extreme
environments – e.g. boiling water.
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Europa as an Abode for Life
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Europa's ocean is likely habitable if life
formed there.
Interestingly, it is now thought that life on
Earth may have originated near
submerged volcanic vents.
The most primitive life forms on Earth
thrive in extreme environments – e.g.
boiling water.
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Exploring Europa's Ocean
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A few decades from now?