Transcript No Slide Title

Formation of Our Solar System
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Image: Lunar and Planetary Laboratory:
http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=178
Some data to explain:
1. Planets isolated
2. Orbits ~circular / in ~same plane
3. Planets (and moons) travel along orbits in same
direction…. same direction as Sun rotates (CCW)
Venus slowly rotates CW
Uranus on its side
Pluto on its side – captured asteroid
Moons go CCW around planets
(few exceptions)
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Lunar and Planetary Institute image at
http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=175
Solar System is highly
differentiated
• Terrestrial planets
– Slow rotators, few or no moons
• Gas Giants
– Fast rotators, many moons
• Asteroids
– Old
– Different from rocky or gaseous planets
• Comets
– Old, icy
– Do not move on same plane as planets
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• Planets, most moons, and asteroids
revolve around the Sun in the same
direction (CCW)
• They all move in ~ circular orbits
• Pluto-special case
– Orbit is highly inclined (18°)
– oval shape
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Some more data to explain:
4. Most planets rotate in this same direction
Mercury 0°
25°
Jupiter 3°
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Venus 177°
Saturn 27°
Earth 23°
Mars
Uranus 98°
Neptune 30°
NASA images edited by LPI
And some more data to explain:
5. Solar System highly differentiated:
Terrestrial Planets (rocky,
dense with density ~4-5
g/cm3)
Jovian Planets (light,
gassy, H, He, density 0.72)
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Images: Lunar and Planetary Laboratory:
http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=178
How Did We Get a Solar System?
Image: LPI
Active region of Star formation in the Large Magellanic Cloud (LMC) – satellite galaxy of
Milky Way
(Hubble)
Huge cloud of cold, thinly
dispersed interstellar gas and dust
(mostly H & He)
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Hubble image at
http://hubblesite.org/newscenter/archive/releases/nebula/emission/2006/41/image/a/
How Did We Get a Solar System?
Image: LPI
Concentrations of dust and gas in
the cloud; material starts to collect
(gravity > magnetic forces)
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Hubble image at
http://hubblesite.org/newscenter/archive/releases/nebula/emission/2005/35/image/a/
How Did We Get a Solar System?
Gravity concentrates
most stuff near center
Heat and pressure
increase
Collapses – central
proto-sun rotates faster
(probably got initial
rotation from the cloud)
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Image: LPI http://www.lpi.usra.edu/education/timeline/gallery/slide_1.html
How Did We Get a Solar System?
• Rotating, flattening,
contracting disk - solar
nebula!
Equatorial Plane
Orbit Direction
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NASA artwork at http://en.wikipedia.org/wiki/Image:Ra4-protoplanetary-disk.jpg
How Did We Get a Solar System?
• After ~10 million years, material in center of nebula hot
enough to fuse Hydrogen (H)
• “...here comes the Sun…”
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NASA/JPL-Caltech Image at
http://www.nasa.gov/vision/universe/starsgalaxies/spitzer-20060724.html
How Did We Get a Solar System?
• Metallic elements (Mg, Si,
Fe) condense into solids
at high temps. Combined
with Oxygen to make tiny
grains
• Lower temp (H, He, CH4,
H2O, N2, ice) - outer
edges
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Planetary Compositions
Hubble photo at
http://hubblesite.org/newscenter/archive/releases/star/protoplanetary-disk/2005/10/image/a/layout/thumb/
How Did We Get a Solar System?
Inner Planets:
• Hot – Silicate minerals, metals, no light elements, ice
• Begin to stick together with dust  clumps
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Image: LPI http://www.lpi.usra.edu/education/timeline/gallery/slide_3.html
How Did We Get a Solar System?
Outer Solar System
• Cold – ices, gases – 10x more particles than inner
• May have formed icy center, then captured lighter
gases (Jupiter and Saturn first? Took H and He?)
• Leave C,O, and N for the others
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Image: LPI http://www.lpi.usra.edu/education/timeline/gallery/slide_5.html
• Terrestrial planets
– Heavier elements stable at higher temperature
– Condensed in inner nebula
• Gas giants
– Lighter elements (H, He, C, O, N) stable at
lower temperature
– Condensed in outer nebula
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Where do Comets Originate?
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• Orbital paths of comets
– Highly elliptical (oval-shaped)
– 1 complete orbit is called a period
– Short-period comets
• Revolve around the Sun less than 200 yrs
• E.g. Comet Halley
• Paths are close to the same plane of orbit
as planets
• Orbit is the same direction as the Sun
• Originate from the Kuiper belt
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• Long-period comets
– Longer than 200 years to go around once
– Orbital path is random
• Direction and plane of orbit
– E.g. Comet Hale-Bopp
– Originated in Oort cloud
• Spherical cloud, 20 trillion miles beyond the
Sun
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How Did We Get a Solar System?
• Accretion - particles collide and stick together … or
break apart … gravity not involved if small pieces
• Form planetesimals, up to a few km across
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Image: LPI http://www.lpi.usra.edu/education/timeline/gallery/slide_3.html
How Did We Get a Solar System?
• Gravitational accretion: planetesimals attract stuff
• Large protoplanets dominate, grow rapidly, clean
up area ( takes ~10 to 25 My)
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Image: LPI http://www.lpi.usra.edu/education/timeline/gallery/slide_4.html
• Smaller protoplanets (inner solar nebula)
– Unable to accrete gas because of their higher
temperature
– Obtain their atmospheres from the impact of
comets
• Largest protoplanets (outer solar nebula)
– Accrete gas because of their cooler
temperature
– Strongly influence the orbits of the remaining
comets
• Either send them out to the Oort cloud or
• Send them inward where they collide with
the terrestrial planets
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How Did We Get a Solar System?
The Asteroid Belt
? Should have been a planet instead of a debris
belt? Jupiter kept it from forming
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Eros image at
http://solarsystem.nasa.gov/multimedia/gallery.cfm?Category=Planets&Object=Asteroids&Page=1
How Did We Get a Solar System?
Beyond the Gas Giants - Pluto, Charon and the
Kuiper Belt objects
Chunks of ice and rock material
Little time / debris available to make a planet –
slower!!
Taken from Hubble Telescope
Charon is Pluto’s moon, only a
Little smaller than Pluto
Pluto’s surface temp. is as low
as -400° F
From the surface of Pluto, the
Sun looks like a very bright
star
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Early in the Life of Planets
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Planetesimals swept up debris
Accretion + Impacts = HEAT
Eventually begin to melt materials
Iron, silica melt at different temperatures
Iron sank – density layering
Image from LPI: http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=168
Mercury
• Average density of 5430 kg/m3
• Second highest density of all planets
• Like Earth, has an Iron core
– 2/3 to ¾ of the radius of the planet!
– Iron-Nickel core
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Venus
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Composition ~ to Earth
Crust 10-30 km thick
Mantle
Core – Iron-Nickel
Average density is 5240 kg/m3
Earth
• Crust, mantle, and core
• Crust
– ~ 30 km thick for land (granite)
– ~ 5 km for oceanic crust (basalt)
• Mantle
• Core, Iron-Nickel
– Liquid outer core
– Inner solid core
• Average density ~ 5520 kg/m3
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Mars
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~ ½ the diameter of Earth
Crust
Mantle
Core ,
– Iron-Nickel
– and Iron sulfide
• Density ~ 3930 kg/m3
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Pluto
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Structure not very well understood
Surface is covered with methane ice
Surface temp ~ 400° F
Frozen methane shows a bright coloration
Density ~ 2060 kg/m3
– This low of a density suggests that the planet
must be a mix of rock and ice
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