ASTR 321 Exam 2

How does a crater get formed

Crater gets formed by shockwave, not the plowing impact.

What angle causes non circular craters?

Less than 10 → 5-6 usually

Impact signatures : Fragments

Big pieces of meteorite & other ejected sub surface rock

Impact Signatures : Meteorite

Iron is more likely to stay, only about 4% of impacts have physical meteorite left

Impact Signatures : Shockwave

Changes mineral grains → shocked quartz

Impact Signatures : Secondary Craters

Material falling on primary object

Impact Signatures : Surface expression

Look like crater on surface but often features are buried

Impact Signature : Global Effect

Earth has layer of biology and impacts change biology, hard transitions in rock show fast change like impact

Iridium anomaly

Think 1cm layer with tons of iridium, only way to explain is to drop 10km rock on Earth.

Earth impact

10km vacuum as it punches atmosphere then that hole gets filled with rocks as it gets sent all over → led to half of earth being on fire after atmospheric interaction means soot all over sky - no light - kills bottom of food chain.

Where do we find these rocks

Where ever you look, ancient deserts - arctic

Chondrites

Carbon rich gives dark color

Carbonations Chondrites

Composition looks like the sun, we see high in amino acids - Water rich, usually have material modified by water - rich in complex organic compounds that should not exist in >200 degree conditions - never differentiated so they are primative

Individual chondrules

Have been heated and contain CAI which is one of the first things that could heat

Al 26

Super good heat source for early solar system but goes away - CC’s were after all Al 26 was gone

Oxygen Isotopes in CC’s

Do not follow tfl - closer to sun there’s more O16 since photons get absorbed quickly by protoplanetary disk

Ordinary Chondrites

low low iron : 20% -

Low iron : 25% -

High Iron : 30% -

• slightly heated but not fully differentiated - formed before CC’s

Achondrites

had lots of Al 26 - so partly differentiated

Stony Iron

Iron / nickel / olivine - like crust / mantle from other worlds - transition to differentiated worlds

Iron asteroids

50% of all meteorites - super clearly not from earth - resist weathering

Widmanstätten Pattern

Iron / Nickel crystals - show slow cooling and high pressure - like planetary core - big patterns show it cools slow and small patterns show it cooled fast

How to get asteroid size distribution

Looking at lunar craters

Why does some asteroids lack small craters and big craters

Small craters are covered due to shaking caused from big impacts, big impacts dismantle the worlds

Why gaps in belt

Jupiter resonance - 2:1, 3:1, 4:1 all get kicked out - CC’s are outside of belt & OC’s are in the middle

Processional frequency with Saturn

Causes NEOs - no CC’s

How do these orbits change gravitationally

Yarkovsky Effect - Thermal re-radiation push then hit a resonance and it gets pushed it or out

Why is Mars / Asteroid belt smaller than it should be based on minimum mass model

At one point they’ve lost their mass - material in solar system can only decrease with time

Meteorite Parent Bodies

Most come form small number of bodies - not good statistically - Almost all AC’s come from Vesta

Callisto

Old Cratered world - mostly ice - surface is full of small craters

Rhea / Mimas

Almost all water ice, full of small craters

Ganymede

Light fractured terrain - seems to be modified by tectonics - slightly larger crater counts

Dione

Big fractures on top of cratered surface - Easier to melt ice than rock - similar geologic activity level as moon

Io

Changing satellite due to tidal forces - thin sulfur layer on silicate world

Europa

Minimal impacts - all water ice - Chaotic terrain - big fragments & icebergs - less tidal change could cause surface fractures

Enceladus

99% albedo - Tiny, barely big enough to be sphere but is active with no craters - only plumes at south pole from fractures

Satellite heat sources

Tidal heating - close to resonance - most worlds have deep heating

Chemistry of satellites

Icy surface interacts with the core - plumes and stuff lower mass so lots of activity has to be recent

Titan Atomosphere

Mainly nitrogen & Methane - from natural outgassing - Need star with UV to have this atmosphere -

Titan Surface

Geologically complex - weathering through rain, erosion - wind - sand dunes all over equator - has methane cycle - potential volcanism & tectonics - lacks small craters

Titan subsurface

Surface rotates at different rater as core - super rich in water ice & has many forms of ice

Tholins - Titan

Organic compounds from radiation, clump of atmosphere

Why a Kuiper belt

accretion is so slow for objects moving that slow

Triton

Active volcanism - streaks along south pole - has resurface event every 100 years

Pluto

Some young and some old surface - has tholins too

Why do impacts look different in inner solar system vs outer - Different Source? or different Material?

Different material - These cannot support large impact basins

Long period comets

from Oort cloud - low inclination and low eccentricity

Short period comets

Jupiter family comets - high inclination - high eccentricity

Comet tails

Gas tail : Gas hits solar wind and pushed straight back

Dust tail : Curves behind with orbit

Comet Oxygen Isotopes

Does not match tfl - so not cause of water on earth → rather it was CC’s

Gas planet bands

High pressure zones are storms - more heat causes clouds to form higher, bright areas are upwelling - Can’t see bands & full clouds on S,N,U - ammonia gas rises and cools

Gas planet interiors

Mainly hydrogen - liquid / metallic, like mercury - has seed of rock and ice at center

Magnetic field of gas giants

Rapidly rotating super-conductors - needs to be heated, convecting and spinning

Exoplanet Methods : Radial velocity

Measure Doppler of star and see if it has slight motion toward or away

Bias: Easy to observe big and close planets - would find Jupiter

Exoplanet Methods : Transit

Gets radius not mass - transit timing gets distance

Bias : Easier for bigger planets / smaller stars - maybe Earth & Jupiter

Small planet radius gap / Fulton gap

Most common is super earth / sub-Neptune — Between Neptune & Saturn Sized worlds - gas gets evaporated when close to star

Exoplanet Methods : Secondary Transit

Can get reflected spectra of planet to get atmosphere / composition - look for specular refraction off liquid

Exoplanet Methods : Transit Timing

Some transits happen at different periods - because of drag from other planets

Exoplanet Methods : Microlensing

Unseen mass passes and magnifies light

Bias : least bias - find all solar system

Exoplanet Methods : Direct Imaging

Look for rocks in space in infrared for less star emission -

Bias : good for big planets far from star - none in solar system

Scale Height

measure of how quickly pressure and density decrease with altitude

What effects rate of accretion?

Mainly size of world - proportional to radius squared - also need to know density and velocity - faster and bigger world picks up things quicker - So stuff closer in grows faster

Timing of solar system formation

Needs to form entirely before T-Tauri phase where solar winds blast particles

Outer planet core : Formation

Need to have 10 Earth mass core to capture hydrogen & helium

Why is snow line so important in planetary formation

more things can solidify past it

Pebble accretion

Pebbles form early and they are more dynamic and drift inward meaning more surface density

Nice model :

Jupiter + worlds form out and move in, they change a lot - outer planets all formed close to snow line and then Saturn orbit hit 2:1 with Jupiter, causing chaos - leads to oort cloud and late heavy bombardment