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Solar Nebula Model
•Planets form from disk of gas surrounding
the young sun
–Disk formation expected given angular
momentum in collapsing cloud
–Naturally explains the regular
(counterclockwise) motion
•Makes additional explicit predictions
–Should expect planets as a regular part of
the star formation process
–Should see trends in composition with
distance from sun
–Should see “fossil” evidence
of early steps of planet formation
From our text: Horizons, by Seeds