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

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 Then came Himalia (J VI, 1904), Elara (J VII, 1905), Pasipha (J VIII, 1908), and others by 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” moons of Jupiter (some are retrograde)

Ast 1001, 17 Oct 2007 Saturn has a mob of satellites too.

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 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 ( N 2 )

Ast 1001, 17 Oct 2007 Titan’s interior ( ? )

Ast 1001, 17 Oct 2007 Titan’s atmosphere and surface

Ast 1001, 17 Oct 2007

Re. Saturn and Titan, look up the Cassini and Huygens space probes (2005)

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 Oberon Titania Umbriel Ariel Miranda

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

Next planet: Neptune. Big moon Triton was discovered soon after Neptune was... (1846)

Ast 1001, 17 Oct 2007 Next planet: Neptune. Big moon Triton was discovered soon after Neptune was... (1846) Triton moves backward – in a “retrograde orbit.” This isn’t easy to explain, for such a 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

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 probably formed when small moons or possibly comets approached too close to the gas giant planets, were broken up by tidal forces.

Ast 1001, 17 Oct 2007 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.

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 CH 4, NH 3, H 2 O, 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