Lecture #17: Conservation of Angular Momentum
I. Disk formation
-- the angular momentum is conserved as gas contracts, so any disk component
that it would tend to have (just by chance) would grow and grow
-- the reason the disk grows in mass is that it is shrinking in radius, and
that would cause it to lose angular momentum (which depends on radius) if it
did not also gain mass to compensate
-- eventually all the mass is in the disk, and you have no gas cloud, you
have a disk
II. Star formation
-- once you form a disk, you must draw out some angular momentum to allow further contraction into the central star
-- the processes that extract angular momentum are complex, but probably
involve magnetic fields and jets of material shooting out of the system
III. Planet formation
-- the generation of a disk gives you high density material you can then
form planets from
-- first dust sticks together into larger bits, eventually gravity gets
strong and the process goes very fast
-- planets that form close to the Sun must be highly metallic, since only
metals can form at such high temperatures
-- planets and moons that form about the distance of the Earth from the Sun will by
rocky, because rocks can form at that distance
-- planets and moons that form at Jupiter's distance or farther will tend to be icy
-- Jupiter's ices are not seen, they would have been swallowed up deep inside the huge hydrogen gas envelope, after the core of Jupiter got large enough to
begin attracting the cold hydrogen gas all around
-- Jupiter's moons were not massive enough to attract the hydrogen, or to compete for it with Jupiter's mass, so they don't have the hydrogen envelope and they are very icy
-- internal heating processes (see tidal effects) can melt these ices in the
interior of Jupiter's moons, particularly Io and Europa. Io is volcanic, Europa has ice plates sitting on top of what is likely liquid water.