Download Solar System

Solar System
•  Sun, 8 planets,
hundred moons,
thousand.dwarf.planets
million asteroids,
billion comets etc.
Comparative Planetology
•  Compares planets and other solar system bodies to help
understand how they formed and evolved
•  Diameters: 10 times Earth=Jupiter & 10Jupiters=Sun
•  Distances: Sun-Earth=8light-minutes & Sun-Jupiter=1Hour
Solar System Looks Like a Disk
•  As the planet’s distance from the sun increases; circumference of
orbit increases & velocity decreases so period of orbit increases
•  Planets revolve in orbits that are tilted less than 7° to sun’s equator
•  Planets ALL orbit in same direction
•  As Sun rotates
Obliquity of Rotation Axes
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Most planets rotate counter-clockwise
Most planets rotation axis is perpendicular to ecliptic plane
Sun’s rotation axis tilted by 7°
But why is Uranus tilted ~90°?
Why does Venus rotate retrograde=clockwise?
Two Kinds of Planets
•  Planets are relatively isolated
•  Terrestrial planets- 4 inner planets
•  Jovian planets – 4 outer planets
Terrestrial Planets
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Mercury, Venus, Earth, Moon, Mars,
Located closer together near sun
Smaller, denser, rocky
Solid surface & Weak magnetic field
Little or no Hydrogen and Helium
Few moons, no rings
Jovian Planets
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Jupiter, Saturn, Uranus, Neptune
Widely spaced in outer solar system
Larger, gaseous, containing Hydrogen & Helium like Sun
Dense atmosphere with no surface & Strong magnetic field
Many satellites, ring systems
Average Density of Planets
•  Density is mass divided by volume – How heavy per volume
•  Terrestrial Planets more dense than Jovian gas giants
•  Problem is moon is not as dense (3.4gm/cm3) as Earth (5.5)
Interplanetary Matter
•  Planets have cleared their orbits, but there’s debris leftover
•  Comet & Asteroid dust ~40,000 tons/year falls to Earth
•  Seen as Zodiacal Light
Asteroids = Minor Planet
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Rocky, smaller than the moon; larger than 100meters diam.
Not enough gravity to pull them into spherical shape
Ceres~1000km diam; Vesta~500km; 15>250; ~million >1km
Movie of Eros
Asteroid Belt
•  Asteroids, Near Earth Objects,
Comets
•  Millions of asteroids generally
orbit between Mars and Jupiter
•  Over 444,080 with good orbits
•  Named by discoverer
•  1 named after UVic and 14
others named after UVic people
Kuiper Belt Region
•  More than 1000 icy objects like
Pluto in Kuiper Belt @ 30-50?AU
Comet: Hale-Bopp 1997
•  Dirty snowball; leftover from
formation of solar system
•  Nucleus 1-10km
•  Ices melt/steam when close to sun
•  Forms million km long tail
Oort Cloud
•  Trillions of comets in
orbits of ~a light year
•  1000 times further than
Kuiper belt
Meteorites
•  Peekskill meteorite or fireball
•  1992 New York; Bright as full moon
•  Meteorite on ground, meteor in air and
meteoroid in space
•  Pinhead sized rocks burn up ~80km up
•  Some leftover from formation of Solar
System
Radioactive Dating
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Clocks start at time of solidifying and reset by melting
238U radioactive decays to 234Th → 206Pb
With half-life of 4.5billion years
We have rock samples of the Earth, Moon, Mars, meteorites
All date to maximum of ~4.6 Billion years
Time of formation of Solar System
Spacecraft
Missions Show
New Worlds
•  Mercury– 1 flyby& 1 orbiter
•  Venus–many flyby, 4.orbiters
•  Mars – many orbiters,
4.landers & 4 rovers
•  Jupiter, Saturn, etc. – 4 flyby
& 2 orbiters
Gravity Assist
•  Throws ball on
parked car
•  Throws ball on
moving car
•  Throws ball on
orbiting car
Pale Blue Dot
•  Voyager 1 looks back
and takes a picture of
the Earth
•  Gives us perspective
What are the characteristic properties
of the solar system that a theory of its
formation needs to explain:
a)  Planets isolated in space=cleared orbit
b)  Disk shape of solar system- small orbit inclination; prograde
circular motion; same tilt&direction of rotation axes (almost)
c)  Jovian/Terrestrial planets: low/high density, huge/small
atmospheres, fast/slower rotation rates, many/few moons &
rings and Space Debris – icy comets, rocky asteroids,
meteoroids, Kuiper Belt
d)  Earth, Moon, Mars, Meteorites, Sun; all 4.6 billion years old
e)  All of the above
Trans-Neptunian Objects
•  Objects which orbit the sun beyond Neptune
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
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?
Debris Disk
•  After the dense disks that
form planets
•  Cold disks of dust are left
•  Made from asteroid
collisions & comet’s tails
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
Atmospheric Escape
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More massive planets have higher Escape Speed
Hotter planets have faster moving air molecules
Heavier molecules move more slowly
Atmosphere can leak into space over eons of time