MOONS SATELLITES

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MOONS ( SATELLITES) of the Gas
Giant Planets
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JUPITER Numerous satellites... Discovered
by Galileo, 1610 Io (a.k.a. J I)
Europa (J II) Ganymede (J III)
Callisto (J IV) For almost 300 years,
they were the only known Jovian satellites
(Jovian means belonging to Jupiter).
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Jupiter and the orbits
of Io Europa Ganymede
Callisto
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(Digression) Ole Roemer, Jupiters moons,
and the speed of light, 1675
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Earth Jupiter distance
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Io Europa Ganymede
Callisto
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Likely interior of Ganymede (theoretical?)
ice-covered surface
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JUPITER At least 57 known satellites In
1892, E. Barnard discovered Amalthea (J V)
-- a small captured asteroid inside the
orbit of Io.
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Amalthea about 200 km across ( same size
as a large asteroid )
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... Then came Himalia (J VI, 1904),
Elara (J VII, 1905), Pasipha (J
VIII, 1908), and others -- 14 by 1979.
Probably all captured asteroids, relatively
small. Then the first spacecraft reached
Jupiter and began to find lots more.
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(Jupiters moons, continued) A random
selection Erinome (J XXV), Thyone (J
XXIX), Hegemone (J XXXIX), Karpo (J
XLIV), etc. etc. The names dont really
matter.
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Orbits of some of the other moons of Jupiter
(some are retrograde)
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Saturn has a mob of satellites too.
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TITAN (the big one) plus IAPETUS, RHEA,
DIONE, TETHYS, etc.
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Dione and Tethys -- icy surfaces
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Mimas -- about 400 km across
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TITAN IS DIFFERENT.
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TITAN IS DIFFERENT.
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1943 spectrum of Titan Methane. It has
an atmosphere!
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But Titan has low gravity.
How can it hold an atmosphere??

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But Titan has low gravity.
How can it hold an atmosphere??
Answer Its cold 94 K
-290 F.
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Saturn as seen from Titan (1944 painting)
blue sky!
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Spacecraft view of TITAN. -- Methane and
ethane clouds --
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Titans atmosphere is mostly nitrogen ( N2 )

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Titans interior ( ? )
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Titans atmosphere and surface
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Re. Saturn and Titan, look up the Cassini
and Huygens space probes (2005)

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Next planet out Uranus.
Soon after discovering Uranus, William
Herschel found that it had
several moons ...
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Oberon Titania Umbriel Ariel Miranda

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(Uranus satellites) Oberon Titania Umbriel
Ariel Miranda ... Later discovered by
spacecraft Ophelia Rosalind Portia Juliet
Rosalind Bianca Cordelia Caliban Puck
Prospero -- and others. At least 27 so far.

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Next planet Neptune. Big moon
Triton was discovered soon after Neptune was ...
(1846)
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Next planet Neptune. Big moon
Triton was discovered soon after Neptune was ...
(1846) Triton moves backward in a
retrograde orbit. This isnt easy to explain,
for such a large moon.
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Spacecraft image of Triton
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Neptune also has the usual horde of smaller
satellites Nereid, Galatea, Naiad,
Proteus, and others. Half of them were
discovered by the Voyager 2 spacecraft when it
passed that planet in 1989.
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Planetary RINGS
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Narrow rings of Uranus -- discovered
in late 1970s --
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Neptune too
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And even Jupiter!
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In general, planetary rings were probably formed
when small moons or possibly comets approached
too close to the gas giant planets, were broken
up by tidal forces.
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In general, planetary rings were probably formed
when small moons or possibly comets approached
too close to the gas giant planets, were broken
up by tidal forces. Saturn is an unusually
dramatic example.
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Satellite names worth remembering
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Satellite names worth remembering PHOBOS
DEIMOS -- asteroids captured by Mars
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Satellite names worth remembering PHOBOS
DEIMOS -- asteroids captured by Mars IO
-- Jupiters moon heated by tidal forces
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Satellite names worth remembering PHOBOS
DEIMOS -- asteroids captured by Mars IO
-- Jupiters moon heated by tidal forces TITAN
-- Saturns moon with dense atmosphere
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Satellite names worth remembering PHOBOS
DEIMOS -- asteroids captured by Mars IO
-- Jupiters moon heated by tidal forces TITAN
-- Saturns moon with dense atmosphere
TRITON -- mysterious retrograde orbit
around Neptune
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Also remember Objects beyond Jupiter tend to be
icy, or at least they have icy outer layers.
(ice can mean CH4 , NH3 , H2O , and maybe
other frozen or slushy stuff)
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We havent mentioned Pluto yet. Thats not
because we forgot it turns out that Pluto is
a different, unfamiliar type of object !
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