Ast 1001, 17 Oct 2007

Ast 1001, 17 Oct 2007

MOONS (= SATELLITES)

of the Gas Giant Planets

Ast 1001, 17 Oct 2007

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).

Ast 1001, 17 Oct 2007

Ast 1001, 17 Oct 2007

Jupiter and the orbits of Io Europa Ganymede Callisto

Ast 1001, 17 Oct 2007

(Digression)

Ole Roemer, Jupiter’s moons, and the speed of light, 1675

Ast 1001, 17 Oct 2007

Earth – Jupiter distance

Ast 1001, 17 Oct 2007

Io Europa Ganymede Callisto

Ast 1001, 17 Oct 2007

Likely interior of Ganymede

(theoretical?)

ice-covered surface

Ast 1001, 17 Oct 2007

JUPITER: At least 57 known satellites

In 1892, E. Barnard discovered

Amalthea (J V) -- a small captured

asteroid inside the orbit of Io.

Ast 1001, 17 Oct 2007

Orbit of Amalthea (J V)

Ast 1001, 17 Oct 2007

Amalthea: about 200 km across ( same size as a large asteroid )

Ast 1001, 17 Oct 2007

... 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.

Ast 1001, 17 Oct 2007

(Jupiter’s moons, continued)

A random selection:

Erinome (J XXV), Thyone (J XXIX),

Hegemone (J XXXIX), Karpo (J

XLIV),

etc. etc. The names don’t really

matter.

Ast 1001, 17 Oct 2007

Orbits of some of the “other” moonsof Jupiter (some are retrograde)

Ast 1001, 17 Oct 2007

Saturn has a mob of satellites too.

Ast 1001, 17 Oct 2007

Ast 1001, 17 Oct 2007

TITAN (the big one); plus

IAPETUS, RHEA, DIONE, TETHYS, etc.

Ast 1001, 17 Oct 2007

Dione and Tethys -- icy surfaces

Ast 1001, 17 Oct 2007

Mimas -- about 400 km across

Ast 1001, 17 Oct 2007

TITAN IS DIFFERENT.

Ast 1001, 17 Oct 2007

TITAN IS DIFFERENT.

Ast 1001, 17 Oct 2007

1943 spectrum of Titan:

Methane. It has an atmosphere!

Ast 1001, 17 Oct 2007

But Titan has low gravity. How can it hold an atmosphere??

Ast 1001, 17 Oct 2007

But Titan has low gravity. How can it hold an atmosphere?? Answer: It’s cold:

94 ° K = 290 ° F.

Ast 1001, 17 Oct 2007

“Saturn as seen from Titan” (1944 painting) blue sky!

Ast 1001, 17 Oct 2007

Spacecraft view of TITAN.

-- Methane and ethane clouds --

Ast 1001, 17 Oct 2007

Titan’s atmosphere is mostly nitrogen

( N2 )

Ast 1001, 17 Oct 2007

Titan’s interior ( ? )

Ast 1001, 17 Oct 2007

Titan’satmosphereand

surface

Ast 1001, 17 Oct 2007

Ast 1001, 17 Oct 2007

Re. Saturn and Titan, look up theCassini and Huygensspace probes (2005)

Ast 1001, 17 Oct 2007

Ast 1001, 17 Oct 2007

Next planet out: Uranus.

Soon after discovering Uranus,

William Herschel found that it had several moons ...

Ast 1001, 17 Oct 2007

OberonTitaniaUmbrielArielMiranda

Ast 1001, 17 Oct 2007

(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.

Ast 1001, 17 Oct 2007

Ast 1001, 17 Oct 2007

Next planet: Neptune.

Big moon Triton was discovered soon afterNeptune was ... (1846)

Ast 1001, 17 Oct 2007

Next planet: Neptune.

Big moon Triton was discovered soon afterNeptune was ... (1846)

Triton moves backward – in a “retrogradeorbit.” This isn’t easy to explain, for sucha large moon.

Ast 1001, 17 Oct 2007

Spacecraft image of Triton

Ast 1001, 17 Oct 2007

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.

Ast 1001, 17 Oct 2007

Planetary RINGS

Ast 1001, 17 Oct 2007

Ast 1001, 17 Oct 2007

Narrow rings of Uranus -- discovered in late 1970’s --

Ast 1001, 17 Oct 2007

Neptune too

Ast 1001, 17 Oct 2007

And even Jupiter!

Ast 1001, 17 Oct 2007

In general, planetary rings were probablyformed when small moons or possiblycomets approached too close to the gasgiant planets, were broken up by tidalforces.

Ast 1001, 17 Oct 2007

In general, planetary rings were probablyformed when small moons or possiblycomets approached too close to the gasgiant planets, were broken up by tidalforces. Saturn is an unusually dramaticexample.

Ast 1001, 17 Oct 2007

Ast 1001, 17 Oct 2007

Satellite names worth remembering

Ast 1001, 17 Oct 2007

Satellite names worth remembering

PHOBOS & DEIMOS -- asteroids captured by Mars

Ast 1001, 17 Oct 2007

Satellite names worth remembering

PHOBOS & DEIMOS -- asteroids captured by Mars

IO -- Jupiter’s moon heated by tidal forces

Ast 1001, 17 Oct 2007

Satellite names worth remembering

PHOBOS & DEIMOS -- asteroids captured by Mars

IO -- Jupiter’s moon heated by tidal forces

TITAN -- Saturn’s moon with dense atmosphere

Ast 1001, 17 Oct 2007

Satellite names worth remembering

PHOBOS & DEIMOS -- asteroids captured by Mars

IO -- Jupiter’s moon heated by tidal forces

TITAN -- Saturn’s moon with dense atmosphere

TRITON -- mysterious retrograde orbit around Neptune

Ast 1001, 17 Oct 2007

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)

Ast 1001, 17 Oct 2007

We haven’t mentioned Pluto yet.

That’s not because we forgot; it turns

out

that Pluto is a different, unfamiliar

type

of object !

Ast 1001, 17 Oct 2007