Download Characteristic Properties

Characteristic Properties- Solar System
1.  Planets isolated in space=cleared orbit
2.  Disk shape of solar system- small orbit inclination; prograde circular
motion; same tilt&direction of rotation axes (almost)
3.  Jovian/Terrestrial planets: low/high density, huge/small atmospheres,
fast/slower rotation rates, many/few moons & rings
4.  Space Debris – icy comets, rocky asteroids, meteoroids, Kuiper Belt
5.  Common ages of Earth, Moon, Mars, meteorites, Sun
Tidal=Passing Star Hypothesis
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Buffon in 1745
•  Catastrophic process
•  Low probability of encounter
•  Hot gasses would dissipate
before they could condense
•  Predicts few stars with
planets
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Nebular Theory
Descartes 1644 envisioned vortices
Laplace 1796 added Newton’s gravity
Evolutionary process
Sun and planets formed from a “vast
rotating cloud of gas and dust called the
solar nebula”
Solar Nebula
•  All the stars form from dust clouds
•  Most dust &gas falls on Protosun
•  Cloud is spinning so dust falls in faster
along poles forms protoplanetary disk
•  Lumps in disk become planets
•  Predicts the many stars with planets
Protoplanetary Disks =Proplyds
•  Sun & planets clean out inner disk ending planet building
•  2MASS and Gemini AO observations of binary star with disk
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5 disks in Orion Nebula
NOT evidence that the planets formed
in a disk surrounding the Sun is:
a)  The planets orbits are inclined only a few degrees
to the equator of the Sun (=ecliptic)
b)  The planets all orbit in the same direction as the
Sun rotates
c)  We see protoplanetary disks around other stars in
star formation regions
d)  We see many extrasolar planets as predicted by the
Solar Nebula Theory which includes disks
e)  The Solar Nebula Theory by Laplace & Descartes
Kepler-56
•  Has 2 planets not in equatorial plane of star
•  Companion star pulls on planets & misaligns them
Protosun
•  Most of the material fell to the
centre of the Solar Nebula forming
the Sun in ~100 Million years
•  Becoming a star with hydrogen
fusion in its core
Condensation
Theory
•  Shuttle experiment done in
no gravity found dust forms
grains very quickly around
condensation nuclei
•  A layer of atoms condenses
at a time to form snowflakes
Hot Disk and Frost Line (Snow Line)
•  Gas & dust in solar nebula heated by protosun
•  Nebula is hotter closer to sun and colder in outer orbits
•  Beyond frost line, H2O forms snowflakes & Jupiter
Condensation
Temperature
•  Metals freeze out first,
then rock, then ices
•  Planets close to sun form
from metals, then rocks,
then ice
•  Density of planets goes
from dense to less dense
•  Terrestrial to Jovian
Accretion
•  Gradual growth by
collision & sticking
•  Snowflakes become
snowballs
Planetesimals
•  Eventually massive enough
to grow by gravity
•  A few kilometers in size
•  Pandora & Hyperion; Low
density moons of Saturn
Protoplanets
•  The more massive they are – the more planetesimals they
collect; the faster they grow
•  At more than 15 earth masses gravitational collapse starts
•  Capturing Hydrogen and Helium directly from nebula
Core-Accretion /
Gravitational Instability Model
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Disk blown away by sun and other stars in a few million years
Core accretion model= (Iron+rock+ice) core then gas – too slow
Disk Instability=Density enhancement draws in gas directly from disk
Movie by Phil Armitage 2005 shows density waves excited by planet
Migrating
Planets•  Encounters with
planetesimals sweep/
eject planetesimals into
asteroid belt, Kuiper
belt, Oort cloud
•  Move Jovian planets
out/in depending on if
they pass in front or
behind planet
Planetary Migration
•  Jupiter and Saturn may have formed
much further from Sun & moved in
•  Uranus and Neptune moved further
out from Sun
Fragmentation
•  High speed collisions between
protoplanets & planetesimals
creates a debris disk
•  P/2010A2 comet? Collision of
2 small asteroids
Debris Disk
•  Not the dense protoplanetary
disks that form planets
•  Cold debris disks are left
•  Made from asteroid, comet,
planetesimal collisions
Large Impacts
•  In final stages a planet would
have had many collisions with
bodies the size of planets
•  Such impacts could tilt the
rotation axis of Uranus, Pluto +
rotation speed of Venus
•  Solar system is like a full coffee
cup – some coffee probably got
spilled
Processes That • 
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Cleared the
Inner Solar • 
System
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Radiation pressure from sun&stars
Protosun’s wind (&stellar) blows
away gas & dust
Planetesimals incorporated into
planets or ejected
All done in millions of years
Overview of Planet Formation
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Common orbital and rotation direction & plane =>protoplanetary disk
Jovian / Terrestrial => range of temperatures in disk / frost line
Interplanetary debris left over from formation = asteroids, comets,
Common ages => simultaneous formation in disk
Collisons of protoplanets = irregularities in Solar System
The main reason terrestrial planets are
more dense than Jovian planets is:
a)  The Jovian planets migrated thru the disk more
b)  The Jovian planets formed outside the frost line
c)  The less dense compounds rose to the outer orbits
d)  The solar wind blew away the terrestrial planet’s
less dense elements
e)  The protosun absorbed all the less dense elements
in the inner solar system so none were left for the
terrestrial planets
Chemical Differentiation
of Planets
•  Young planet very hot
due to impact heating
(=heat of formation)
•  +Radioactive decay in
core of planet
•  Iron, Nickel, Iridium
settle to the core
•  Silicates rise above
iron
•  Ices/water next
Outgassing
•  Water, carbon dioxide, sulfur dioxide, nitrogen released by
volcanoes
•  Forms atmosphere
Angular Momentum
Problem
•  The protosun rotates rapidly and has
huge convection cells so it generates a
strong magnetic field
•  The magnetic field tries to accelerate
the disk and solar wind, slowing
rotation by magnetic braking
•  Observations of stars with known ages
in Hyades etc. show that the older stars
rotate more slowly
Late Heavy Bombardment
•  Late Heavy Bombardment second
surge in impacts
•  When Jupiter, Saturn, Uranus,
Neptune change orbits scattering
planetesimals?
MOST: Jaymie Matthews UBC
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Observed HD209458 for months and
Saw no eclipses from Earth sized planets
Timed transits showing no Earth sized planets-so far
No opposition effect so low 50% albedo
Comet Lulin
•  Dirty Snowball or
Icy Mudball
•  Nucleus ~10km
•  Tail ~1 million km
•  3572 comets – 2000
short period
Comet NEAT 29Jan & 2Feb03
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Dirty snowball or maybe icy mud ball is better
Nucleus ~ 10km
Tail ~1,000,000km to 1 astronomical unit
Very eccentric elliptical orbit
Coronographic Image of Debris Disk
•  Star is masked by black spot in original and untilted image
•  Notice cleared inner disk(30AU) and spiral wave features
•  ~320 light years distance, 300AU diameter, 5 Million years old
Gravity Assist
•  Throws ball on
parked car
•  Throws ball on
moving car
•  Throws ball on
orbiting car
Impact Crater Formation
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Impactor has velocity 10 times rifle bullet
Releases energy 10 times equal mass of dynamite
Impactor vaporized when temperature reaches millions K
Shock wave forms shocked quartz found only in impacts
Rebound can launch rocks without destroying them
Rocky Surfaces Saturated with Craters
•  Planets formed from
many meteorite impacts
•  Circular craters due to
explosion caused by
impact
•  Solar System “Full”?
Erosion of Craters
•  Craters hidden by:
1. Volcanoes – lava flows
2. Continental drift
3. Erosion by atmosphere
4. Oceans
Younger Terrain = Fewer Craters
•  The larger the terrestrial world; the more internal
heat it will retain = higher temperature in core
•  The higher temperature; more geologically active so
more craters are covered = fewer craters showing
•  Older terrains = more craters
Comet Impacts on Jupiter
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Painting shows Jul94 impacts of Comet Shoemaker-Levy 9
HST photo from 20Jul09
Comets deposit ice
Heating planet
03Jun10
Jupiter Impact
•  Last June Jupiter
became a little more massive
•  Two amateur astronomers
recorded the impact
•  2009 impact left scar
•  Notice missing SE belt
Planetary Magnetic Fields
•  Jovian planets plus Earth have magnetic fields
•  Various directions and strengths and offsets
Planetary Dynamo
•  Conducting, convecting/circulating, rotating core
generates magnetic field
•  Earth: Iron core; Jupiter: liquid metallic hydrogen
•  Uranus, Neptune: water with ions
Magnetometer
•  Measures the strength & direction of Magnetic field
•  Can probe the interior of the “planet”
Elemental Abundances
•  Element determined by number
of protons=atomic number
•  Neutrons determine Isotope
•  Elemental abundances on Earth
•  Not the same as in stars, Jupiter,
Saturn
Elements Forged In Star’s Cores
•  You are made of
star dust
•  Stars have died so
you may live
Chondrules
•  Many meteorites contain small glassy inclusions
•  Formed by rapid melting and solidified in hours
•  Chondrules date from formation of Solar System