Origin of the Solar System Born with the

Origin of the Solar System Born with the Sun

Big Picture! The solar system was born from the gravitational contraction of a large, rotating cloud of gas and dust some 4. 6 Gy ago.

Elements of a Model • Dynamical properties (motions) • Chemical properties (composition) • Formation of planets, satellites, and other stuff • Evolution of planets, satellites, and other stuff

Nebular (“Cloud”) Model • Origin: Rotating interstellar cloud of gas and dust • Contraction: Self gravity brings cloud together; becomes denser; heats up; forms a disk with bulge in center

Nebular Model • Sun: Forms at center; reflects original composition of cloud • Planets: Form in disk by accretion of smaller bodies; composition determined by local temperature • Debris: Remnants of materials in cloud

Angular Momentum • Tendency for spinning/orbiting mass to continue spinning/orbiting • Total angular momentum constant for an isolated system • Demands that as a spinning cloud contracts, it spins faster & forms disk with central bulge

The Bad News • Planets have too much angular momentum (orbital), sun too little angular momentum (spin) • Way out: Magnetic fields transfer spin from central parts of cloud to out parts while gas in disk still a plasma (hot!)

The Good News • Planets orbit in a plane in near circular paths • Planets orbit and spin in the same direction as original spin • Most satellites and rings orbit and spin in same direction

Formation of Planets • Condensation: Gas => Grains • Accretion: Grains hit & stick, make pebbles, hit & stick, make planetesimals • Gravitational attraction makes planetesimals => protoplanets

Chemical Condensation • Temperature in disk drops rapidly outward from sun • Lowest local temperatures determines what kinds of grains condense: metal, rocks + metals, ices + rocks, ices, gases + ices, gases

Chemical Condensation • Near sun, more metals and rocks (terrestrial); farther out, greater ices and gases (Jovian) • Asteroids: Uncollected “terrestrial” planetesimals • Comets: Uncollected “Jovian” planetesimals