1 Formation of Our Solar System Image: Lunar and Planetary Laboratory: 1

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Formation of Our Solar System

Image: Lunar and Planetary Laboratory: http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=1781

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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)

Lunar and Planetary Institute image athttp://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=175

Venus slowly rotates CWUranus on its sidePluto on its side – captured asteroid?Moons go CCW around planets

(few exceptions)

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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

NASA images edited by LPI

Mercury 0° Venus 177° Earth 23° Mars 25°

Jupiter 3° Saturn 27° Uranus 98° Neptune 30°

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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 0.7-2)

Images: Lunar and Planetary Laboratory: http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=1786

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How Did We Get a Solar System?

Huge cloud of cold, thinly dispersed interstellar gas and dust (mostly H & He)

Hubble image at http://hubblesite.org/newscenter/archive/releases/nebula/emission/2006/41/image/a/

Image: LPI

Active region of Star formation in the Large Magellanic Cloud (LMC) – satellite galaxy of Milky Way(Hubble)

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Concentrations of dust and gas in the cloud; material starts to collect (gravity > magnetic forces)

How Did We Get a Solar System?

Hubble image at http://hubblesite.org/newscenter/archive/releases/nebula/emission/2005/35/image/a/

Image: LPI

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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) Image: LPI http://www.lpi.usra.edu/education/timeline/gallery/slide_1.html 9

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How Did We Get a Solar System?

NASA artwork at http://en.wikipedia.org/wiki/Image:Ra4-protoplanetary-disk.jpg

•Rotating, flattening, contracting disk - solar nebula!

Equatorial Plane

Orbit Direction

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•After ~10 million years, material in center of nebula hot enough to fuse Hydrogen (H)

•“...here comes the Sun…”

How Did We Get a Solar System?

NASA/JPL-Caltech Image at http://www.nasa.gov/vision/universe/starsgalaxies/spitzer-20060724.html 11

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How Did We Get a Solar System?

Hubble photo at http://hubblesite.org/newscenter/archive/releases/star/protoplanetary-disk/2005/10/image/a/layout/thumb/

•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

Planetary Compositions12

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How Did We Get a Solar System?

Inner Planets:•Hot – Silicate minerals, metals, no light elements, ice

•Begin to stick together with dust clumpsImage: LPI http://www.lpi.usra.edu/education/timeline/gallery/slide_3.html 13

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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

Image: LPI http://www.lpi.usra.edu/education/timeline/gallery/slide_5.html 14

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• 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 acrossImage: LPI http://www.lpi.usra.edu/education/timeline/gallery/slide_3.html 19

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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)Image: LPI http://www.lpi.usra.edu/education/timeline/gallery/slide_4.html 20

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• 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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The Asteroid Belt? Should have been a planet instead of a

debris belt? Jupiter kept it from forming

How Did We Get a Solar System?

Eros image athttp://solarsystem.nasa.gov/multimedia/gallery.cfm?Category=Planets&Object=Asteroids&Page=1 23

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Beyond the Gas Giants - Pluto, Charon and the Kuiper Belt objects

Chunks of ice and rock materialLittle time / debris available to make a planet

– slower!!

How Did We Get a Solar System?

Taken from Hubble TelescopeCharon is Pluto’s moon, only a Little smaller than PlutoPluto’s surface temp. is as lowas -400° FFrom the surface of Pluto, theSun looks like a very bright star

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Early in the Life of Planets

• 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

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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

• Composition ~ to Earth• Crust 10-30 km thick• Mantle• Core – Iron-Nickel• Average density is 5240 kg/m3

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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

• ~ ½ the diameter of Earth• Crust• Mantle• Core ,

– Iron-Nickel– and Iron sulfide

• Density ~ 3930 kg/m3

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Pluto

• 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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