Planets

Planet Formation

Dust coagulation

Breaks metre-barrier with streaming instability

Beyond

Within snow line

- Ice and rock

Beyond snow line

- Rocky

Sun turns on

Photons and solar wind

Blows away remaining gas so gas giants can't keep growing

Magnetic fields then slow the star's rotation

Debris disc from all of the planetesimals

The smallish ones now break apart when they collide so make more dust

Metre-scale Barrier

As gas cools, larger worlds form: planetesimals

Have to get from tiny dust to planetesimals to protoplanets and eventually planets

Rotation of particles around star

Has drag from the gas around it slowing orbit

Dust goes from dust to metre-scale within about a year

Metre-scale falls into star or fragments so harder to grow beyond

Problem to get to metre-scale

Speed is high they will bounce or shatter

If speed is low, grains stick together

Solution

Streaming instability

Linear growth as they all spin together and slowly grow

Nonlinear phase concentrating into dense filaments

Gravity of particles overpowers tidal forces

Rock and Ice Worlds

- Interior

Iron core for bigger

Smaller

- Mostly rock and ice

- Might have an atmosphere

- Surface

What affects the surface?

- Volcanism

Types: Silicate, Ice-based

Always pressured material in denser medium

Io is the most active volcanically in our solar system

- Erosion

- Impacts

- Tectonics

Differentiation

Compositional diversity caused by

Heat

Radioactive isotopes

Pressure

Density

Planetesimals have very low density - 3-4x water

And gravity differences

Planetary Observational Bias

We see things close to stars and big ones

Part of this let to seeing a lot of "hot Jupiters"

Giants

Types: Gas, Ice

Orbit Types

Bound, elliptical with an eccentricity less than 1; unbound, parabolic at e = 1 and hyperbolic greater

Migration

3 Types: I, small planets shove spiral waves into disc and gain/lose angular momentum; II, big planet clears a gap around it; III, Large votives bring planets like gas giants in until they hit a dense part of the disc

Resonance

When planets have common or integer multiple periods of eachother

Planetesimals

Small objects; continuum between rocky and icy; lots of debris together so fairly low density; steep size distribution with lots of small

Active Asteroid

Small rocky objects in our Solar System that have asteroid-like orbits but comet-like appearances. Active asteroids can have visible tails and comae — the halo of debris that often surrounds comets

Oort Cloud

a spherical region that surrounds the solar system, that extends from the Kuiper Belt to almost halfway to the nearest star, and that contains billions of comets

Albedo

the percentage of incoming sunlight reflected from a surface. Determined by composition and shape.

Small body populations

Main belt, Trojan (near Jupiter), Kuiper Belt

Requirements for life

RedOx reactions

Solvent/medium (probably water)

Self-replicating material (RNA, DNA)

Time

Impact cratering

Key process for dating surfaces throughout the solar system

Younger surfaces have few craters while older surfaces have more

Crater saturation on really old surfaces

so densely covered with impact craters that the formation of new craters begins to obliterate older ones, reaching quasi-equilibrium

Spin axis/tilts/obliquity for every planet in the solar system tells us about impacts

Comet broken up impacts jupiter eft impact large as earth despit eonly be few km big

GMC protocore contraction

Gas and dust clouds contract due to gravity

Angular momentum conserved - spins faster as it contacts

Material forms spinning disk - protoplanetary

As the gas cools, larger worlds form: planetesimals