Q. 26: What Materials Condensed? Condensation As the cloud shrunk molecules started finding each other If cold enough, they could stick together Proto-Sun created heat – hotter for the inner regions Most of the region was cool enough to have rock and metal begin to form dust grains Vaporizes only around 1000+ K Beyond the “frost line” there were ices mixed in Ices vaporize around 150 K Beyond a few AU it was cool enough to form ices Nowhere cold enough for hydrogen or helium to condense Q. 26: What Materials Condensed?

Collide the Pieces Zillions of bits of dust orbiting the protostar Collisions are inevitable Tiny bits stick together Bits get bigger

Planetismals and Early Planets Small grains of dust stick together Eventually get big clumps - planetismals Gravity slowly begins pulling them together Eventually only a few left - planets Planetismals Planets

What are Early Planets Like? Inside the frost line, only metals and rocks Planets were rocky/metallic About ½% of total mass Outside the frost line, rock, metals and ices About 2% of total mass Creates larger planets The remaining hydrogen and helium gas was still in gaseous form

Primary Atmospheres The early planets are still in a background of hydrogen and helium Gravity will attract atmospheres Larger planets get a lot more Outer planets get a large primary atmosphere of hydrogen and helium Inner planets get a thin atmosphere

Stellar Winds The early Sun starts blowing out excess gas This begins clearing away what is left of the protoplanetary disk The disk gets cleared away

Atmospheres vs. Stellar Winds The wind blows away the remaining gas and dust Only planets and planetismals remain It also can disperse the primary atmospheres More likely with nearby planets More likely with smaller planets Later, other atmospheres may be formed from gasses inside the planets Thin, not hydrogen/helium

Cratering, the Final Touch Largest objects are now planets and minor planets Objects that circle planets are called moons Many small objects still survive Small objects hit the planets and moons At first cratering is fast - eventually slows down When things get resurfaced, craters are wiped out Young terrain has few craters - old terrain has many Pot Holes Q. 27: Jupiter’s moon Io

Differentiation Atmosphere Ice Rock Metal Planets formed from collision of ice, rock, and metal Collision created energy – it melted Heaviest parts fell to the bottom Atmosphere, which is lightest, was then gathered on top Ice Rock Metal

Planets: Hot on the Inside Collision of planetismals created a great deal of heat But mostly, this heat has long since dissipated Differentiation is ongoing and makes a little heat The main source of internal heat now is radioactivity Slow, steady, production of heat inside the planet Heat escapes from the inside of the planet – slowly Therefore, planets are hot on the inside They cool over time Big planets still (partly) liquid on the inside

Planets: Outside Temperature The planets are getting heat from the Sun The closer a planet is to the Sun, the more heat it gets They reradiate this power as thermal energy If this is in perfect balance, and if planet is a perfect blackbody, then the closer a planet is to the Sun, the hotter the surface is Closer planets are hotter Almost always

Keeping Your Atmosphere Gravity holds molecules onto planet If atoms/molecules exceed escape velocity, they leave Lighter molecules move faster Easier to keep heavy molecules Heat is motion of molecules Hot molecules leave Planets/moons that are massive and cold are more likely to have atmospheres Q. 28: Titan’s Atmosphere

Magnetic Fields Flow of charges (electric current) creates magnetic fields Motion needed to regenerate the fields What you need for magnetic fields: A layer that conducts electricity (metal?) It must be liquid Rotation