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Formation of Our Solar System 1 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) 2 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 3 • 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 4 Some more data to explain: 4. Most planets rotate in this same direction Mercury 0° 25° Jupiter 3° 5 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) 6 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) 7 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) 8 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) 9 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 10 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…” 11 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 12 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 13 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 14 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 15 Where do Comets Originate? 16 • 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 17 • 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 18 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 19 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) 20 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 22 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 23 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 24 Early in the Life of Planets • • • • • 25 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 26 Venus • • • • • 27 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 28 Mars • • • • ~ ½ the diameter of Earth Crust Mantle Core , – Iron-Nickel – and Iron sulfide • Density ~ 3930 kg/m3 29 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 30