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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. CH4)
• 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)
>2000K
gases
Ions: atoms, molecules
1400K
Iron & Nickel
1300K
Silicon, Sulfur
Metal Grains (e.g. Fe2O3)
Silicate grains
300K
Carbon
Carbonaceous grains
100-300K
H, C, N, O
Ices (H2O,CO2,NH3,CH4)
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