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Chapter 4 The Solar System Comet Tempel Chapter overview • Solar system inhabitants • Solar system formation • Extrasolar planets Solar system inhabitants • Sun • Planets • Moons • Asteroids • Comets • Meteoroids • Kuiper Belt Objects Figure 4.1 Solar System Planets • • • • • • Orbital size Orbital period Mass Radius Moons Density (water density is 1000 kg/m3) Table 4-1 Properties of Some Solar System Objects Planetary orbits • Lie in same plane (ecliptic plane) • Mercury and Pluto are slight exceptions • Orbit around sun in same direction Figure 4.2 Planetary Alignment Terrestrial planets • Mercury • Venus • Earth • Mars Jovian planets • Jupiter • Saturn • Uranus • Neptune • Memory aid: S-U-N Figure 4.3 - Sun and Planets Table 4.2 - Comparison Between the Terrestrial and Jovian Planets Table 4-2 Comparison Between the Terrestrial and Jovian Planets Other planet? • Pluto • As of late 2006, demoted from a planet Interplanetary matter • Asteroids • Comets • Meteoroids Figure 4.4 Inner Solar System Asteroids • Asteroid belt • Between orbits of Mars and Jupiter • Noticeably elliptical orbits • Trojan asteroids • Earth crossing asteroids • Up to 1000 km in size Figure 4.5 Asteroids, from Earth Figure 4.6 Asteroids, Close-up a) Gaspra b) Ida with Dactyl c) Mathilde Asteroid types • Carbonaceous • Dark, water ice and organics (carbon) • Silicate • Reflective, more rocky • Inner portion of asteroid belt Figure 4.7 Asteroid Eros Discovery 4-1a What Killed the Dinosaurs? Discovery 4-1b What Killed the Dinosaurs? Figure 4.8 Halley’s Comet Comets • Nucleus • Coma (dust and evaporated gas) • Hydrogen envelope • Ion tail • Dust tail • Tails directed away from sun Figure 4.9 Comet Tails - Comet Hale-Bopp 1997 Figure 4.10 Comet Trajectory Figure 4.11 Halley’s Comet Close-up from Giotto spacecraft in 1986 Figure 4.12 a) Comet Wild-2 from Spacecraft Stardust b) aerogel for comet dust Short period comet orbits • Short period (< 200 years) • Kuiper belt (beyond Neptune) • 30 to 100 AU from sun • Roughly circular orbits, in ecliptic plane • Occasionally kicked into inner solar system • About 900 Kuiper belt objects (KBO) known • Some KBO’s larger than Pluto Long period comet orbits • Long period (> 200 years) • Oort cloud • Up to 100,000 AU diameter • Random orbital orientation • Occasionally kicked into inner solar system Figure 4.13 Comet Reservoirs Meteor terminology • Meteoroid (chunk of space debris) • Meteor (streak of light in sky) • Meteorite (piece of meteoroid that falls to ground) • Micrometeoroids • Meteoroid swarm or shower (cometary debris) Figure 4.14 Meteor Trails Figure 4.15 Meteor Showers Table 4.3 Some Prominent Meteor Showers Table 4-3 Some Prominent Meteor Showers Figure 4.16 Radiant Figure 4.16 Analogy Railroad Tracks Converging Meteor craters on earth • About 100 craters over 100 m in diameter • Others heavily eroded by weather or geological activity Figure 4.17 - Barringer Crater, Arizona Figure 4.18 Manicouagan Reservoir, Quebec Figure 4.19 Tunguska Debris (Siberia, 1908) Meteorite types • Rocky silicate • Iron with some nickel • Carbonaceous • 4.4 to 4.6 billion years old Figure 4.20 - Meteorite Samples (a) rocky or stony (silicate) (b) iron and some nickel Model of Solar System formation must explain 1. Each planet isolated 2. Planet orbits nearly circular 3. Planet orbits nearly lie in a plane 4. Planets orbit sun in same direction sun rotates 5. Most planets rotate in same direction sun rotates 6. Most moons revolve in direction planet rotates 7. Terrestrial vs. Jovian planets 8. Asteroids are old and are unlike planets 9. Kuiper belt objects 10. Oort cloud comets Figure 4.21 Angular Momentum Figure 4.22 Beta Pictoris More Precisely 4-1 The Concept of Angular Momentum More Precisely 4-1b Conservation of Angular Momentum Figure 4.23 - Dark Cloud containing interstellar dust and gas Formation of solar system • Nebular contraction • Spinning material flattens into pancake as it contracts • Condensation of interstellar dust • Accretion • Millions of planetesimals • Protoplanets • Fragmentation • Protosun Figure 4.24 Solar System Formation Figure 4.25 Newborn Solar Systems? Jovian planets • Outer planets grew rapidly • Gravitationally attracted gas from solar nebula • Or could have started as gravitational instabilities in solar nebula Figure 4.26 Jovian Condensation Figure 4.27 Temperature in the Early Solar Nebula Figure 4.28 Planetesimal Ejection Figure 4.29 Extrasolar Planet Extrasolar planets • Indirectly detected by motion of star • Large Jupiter-like planets in small orbits • Selection effect • Only detect largest and closest to the star • Is our solar system unique? Figure 4.30 Planets Revealed Figure 4.31 An Extrasolar Transit Figure 4.32 Extrasolar Orbits Figure 4.33 Sinking Planet