The Formation of the Solar System Planetary motions

The Formation of the Solar System

Planetary motions • The Sun, planets, asteroids, comets, planetesimals all revolve in the same direction with some exceptions. • Rotation axes usually perpendicular to orbital plane

Pluto

Planet-Planetesimal composition • Terrestrial Planets: • Cores Small & rocky (refractory elements, silicates & iron) • Atmospheres: Thin, no H/He, some ices or volatiles (C, N, O, Ne) • Jovian Planets: • Cores large rocks/metals/ices • Atmospheres H or H-compounds (e. g. CH 4) • KBOs: planetesimals and icy bodies: • Small ice & rock mixtures with frozen volatiles.

Icy Pluto Rocky Planets Giant Gas Planets Mostly H, He, & Ices

Primordial Gaseous nebula Gas cools and condenses gravitationally into a disk

Proto-Planetary Disks and Star Formation

Primordial Solar Nebula • Rotating solar nebula is composed of • ~74% Hydrogen & 25% Helium • Traces of metals and dust grains • Initially T~2000 K, gas cools to ice and dust according to condensation temperature

Condensation Temperatures T(K) Elements Compounds (oxides, silicates) >2000 K gases Ions: atoms, molecules 1400 K Iron & Nickel 1300 K Silicon, Sulfur Metal Grains (e. g. Fe 2 O 3) Silicate grains 300 K Carbonaceous grains 100 -300 K H, C, N, O Ices (H 2 O, CO 2, NH 3, CH 4)

Snow Line: Separation of Rocks/Metals from Gases/Ices • Rock & Metals form where T < 1300 K • Carbon grains & ices where T(gas) < 300 K • Inner planets and asteroids: Rocky and metallic • Snow line • Outer Jovian systems: Gaseous giants, carbon ices • Dust grains and ices collide, accrete, and eventually grow bigger gravitationally into planetesimals beyond the snow line

Life of the Sun • Burns or converts H He via theromonuclear fusion in core • When hydrogen in the core is exhausted, converted into helium, the H-burning shell moves outward and the star expands • H-burning phase for another 5 billion years; inert He-core • Stars in H-burning phase are said to be Main Sequence stars • Sun Red Giant • Eventually He in the core ignites helium flash • He-burning C/O (carbon, oxegen core) • Core separates from the envelope, which is ejected • Hot core and ejected envelope “Planetary Nebula” (star looks like a ring with bright center; nothing to do with planets) • Central core of planetary nebulae cools White Dwarf

Red Giant Star Inert He Core H Burning Shell Cool, Extended Envelope

Planetary Nebulae Sampler

Death of the Sun • Hot core continues as a white dwarf, about 60% mass of the Sun and size of the Earth • Gigantic diamond in the sky!

The Death of the Sun