Friday April 23th 1999
Announcements:

Lecture notes:

Lecture 42.
 

Moons of Jupiter.
Jupiter has at least 16 moons.  Has 4 main moons known as the Galilean satellites since seen by
Galileo.  Io Europa Ganymede Callisto.
Named after mythical attendants of Roman God Jupiter.
Nearly circular orbits synchronous for all.

Range from slightly smaller than Earth's moon to slightly larger than Mercury ( Ganymede)
Also has lots of smaller moons.  4 inside Io's orbit.  8 outside Callisto's orbit.  -  The outer 8 probably captured as 2 bodies that broke up to make 8 moons.

Galilean Moons
Io Europa have rocky compositions.
Ganymede Callisto deficient in rocky materials probably about 50% water ice.

Io - most geologically active object in entire solar system.  Surface looks like a giant pizza.  Essentially no craters because
always resurfacing itself.  Being tidally stirred up inside by Jupiter's gravity - gets distorted inside - like repeatedly
bending a wire.  Europa's gravitational tugs won't let it circularize.

Europa - also appears to have a youthful surface - few craters.  See fields of water ice with what appears to be fractures in the
ice.  There is reasonable evidence building that Europa may have oceans beneath the ice - eg. Galileo satellite like to speculate
about life in these possible oceans.

Ganymede - largest moon in solar system.  Larger than Mercury Pluto.  Largely water ice.

Callisto - similar to Ganymede but smaller.  Has a big impact basin - Valhalla - 3000km across.

Moons of Saturn
Saturn has most extensive set of moons.  Has at least 18 moons.

3 basic groups.
Small - irregular shaped ice chunks less than 300 km across.
Complex orbits - "interchanges" LaGrange points chaotic rotation.
Medium - six of these.  Diameters from 400-1500 km.  Made of rock and water ice and highly reflective.
Titan - one large moon of Saturn 5150 km.

Titan - Voyager 1 did close flyby since scientists very interested.  Largest of Saturn's moons and 2nd largest moon in
solar system.  Has atmosphere 90% nitrogen and some argon and methane.  Smoggy so can't see surface.  Rocky core surrounded by water ice.  Surface may be covered with lakes of liquid ethane or petrochemical sludge.

Moons of Uranus - 19.2 AU from Sun.
Has at least 15 moons - again ice and rock.
5 major moons and then lots of little ones.  Their orbits are in Uranus's highly tipped equatorial plane and they are tidally
locked so they have extreme seasons too.

Strangest moon is Miranda.  Huge range of surface terrain - ridges valleys faults etc.  Some hypothesize that Miranda has
been blown apart and then reassembled by gravity in a jumbled manner.

Moons of Neptune - 30.1 AU from Sun has at least 8 moons.
2 most interesting ones are Triton and Nereid.
Triton - 2800 km in diameter and orbits retrograde.  6th large moon of outer solar system.  Has a tenuous nitrogen atmosphere
and water ice surface.  Notable lack of cratering - young surface - water volcanoes.  Has nitrogen gas geysers.

Nereid - only 200 km across.  Prograde but eccentric orbit - closest 1.4 million km.  Farthest 9.7 million km.