• TURN IN HOMEWORK #2
• QUIZ THIS WEEK IN DISCUSSION SECTION
• Covers chapters 1-6
• 22 multiple choice test problems (similar to midterm/final)
• 1 longer answer like homework (worth 3 multiple-choice problems)

• Spectral lines reveal:
• Chemical composition
• Temperature
• Relative speed
• Examples
• Saturn's moon Titan has methane (CH₄)
• Europa has water ice

Textbook Figure 7-5b: Titan reflection geometry

Textbook Figure 7-5a: Titan spectrum

Textbook Figure 7-6: Europa Spectrum

• Jovian planets are mostly Hydrogen and Helium (gasses)
• Terrestrial planets are mostly heavy elements like:
• Iron (Fe)
• Silicon (Si)
• Magnesium (Mg)
• Sulfur (S)
• Nickel (Ni)

• (we care because we are made up of them)
• The Universe was formed in the Big Bang
• After a cooling off period, hydrogen and helium were the dominant materials
• Clumps of gas started to form (self gravity)
• Large clumps contracted to become galaxies,
• Clumps within the galaxies contracted to become stars
• Certain types of stars don't live very long, die violent deaths (Supernova)
• Supernova events create and disperse the heavy elements
• We are recycled

• The solar system formed from a clump of gas
• There was enough gas to self gravitate
• As gas clump contracted, it got hotter
• Gas at center got hottest
• Analogy: lecture hall in summer
• became protosun
• Gas doesn't all head perfectly to center
• Rotation
• As gas contracts, spins faster
• Conservation of angular momentum (ice skater illustration)
• Spinning faster causes disk shape
• Think pizza
• We see stars forming in other nebulae
• Disks called protoplanetary disks (proplyds)

Orion Nebula

• The solar protoplanetary disk had clumps
• Clumps merged to become planetesimals
• Small planetesimals accreted onto larger ones which became protoplanets
• Protoplanets merged to become planets as we know them (more or less)

• solids--molecules/atoms locked in
• liquids--molecules/atoms loosely associated
• gas--each molecule/atom independent
• plasma--atoms knocking the electrons out of each other

• Why did some protoplanets turn into terrestrial planets, others into Jovian planets?
• Protoplanets close to protosun were hotter
• Materials with low melting points remained in gas phase (phases of matter primer)
• Water (H₂O)
• Methane (CH₄)
• Ammonia (NH₃)
• Gasses did not stick to early protoplanets (too small, gravity too weak)
• Materials with high melting points were solid and stayed behind
• rock
• iron
• silicates (sand)

• Further from protosun
• Colder
• Protoplanets could use ices (e.g. water, Ammonia) as building blocks
• Protoplanets got bigger
• Big enough to accrete gas
• Lots of gas around so planets got BIG

• Big bang -- Universe mostly hydrogen and helium
• Big clumps form galaxies
• Clumps in galaxies form stars
• Some stars blow up (Supernova) creating and distributing heavier elements
• Material re-clumps, starts rotating, forms protoplanetary disk
• Clumping in disk forms/of planetesimals
• Planetesimals form protoplanets
• Outer protoplanets accrete gas
• Sun burps (T-Tauri wind) which clears remaining gas out of solar system

• Asteroids, aka. minor planets
• Rocky
• Comets (e.g. Hale-Bopp, Halley)
• Icy
• Meteorites
• Various

• If planet(s) are heavy, star gets pulled around
• Detect resulting wobble visually (see it move) or spectroscopically (with the Doppler shift)