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Lecture 2: The Solar System Dr Michael Burton GENS4001 X1 The Solar System 1 Overview • Formation from collapse of cloud of gas and dust 4.6 billion years ago. • Collisions and cratering dominated for first 150 million years, leaving current planetary system. • Inventory: 1 star, 8+1 planets, moons, asteroids, comets, solar wind. • Terrestrial (rock)+ Jovian (gas) planets GENS4001 X1 The Solar System 2 Our Star, the Sun • Giant ball of plasma undergoing thermonuclear fusion of hydrogen in centre! • Photosphere (visible), chromosphere (spicules & granules), corona (solar wind) comprise the atmosphere. • Sunspots, magnetic fields and convection, causing plages, prominences & solar flares. • Solar Model well understood (neutrinos?). GENS4001 X1 The Solar System 3 Mercury • Day is two years long (tidal resonance)! • Cratered surface (impacts), covered by some lava flows. • Iron core and magnetic field. • Atmosphere (Na) from outgassing of planet. GENS4001 X1 The Solar System 4 Venus • Dante’s Inferno: 500°C, 100 atmospheres and sulphuric acid clouds! • Runaway greenhouse hidden by cloud. • Rolling hills, two continents and volcanoes. • Crust periodically melts?! • Slowly rotates backwards with no seasons. GENS4001 X1 The Solar System 5 Earth / Moon • Double planet system, tidally interacting. • Plate Tectonics produces continents, oceans, mountains & volcanoes. • Iron rich core producing magnetic field. • Supports life on land, oceans & atmosphere. • Moon created via collision-ejection. • Weathering erased asteroid impacts on Earth but past history still visible on Moon. 6 GENS4001 X1 The Solar System Mars • No canals, but ancient river channels! • No plate tectonics, resulting in giant shield volcanoes over hot spots, plus canyons. • A few impact craters. • Thin carbon dioxide atmosphere & red dust. • Water must once have flowed. • Could life have once existed? • 2 moons are captured asteroids. GENS4001 X1 The Solar System 7 Jupiter • • • • • • • The Giant of the planets (not a failed star). Rapid, differential rotation. Belts & Zones, methane & ammonia clouds. Cyclones interface: Red Spot & white ovals. Strong magnetic fields, huge aurorae. Gas / Liquid Metallic H / Rocky Core. Thin, transient dust ring - meteor impacts. GENS4001 X1 The Solar System 8 Moons of Jupiter • • • • • 16 Moons with 4 giants (Galilean satellites). Io: Volcanic, molten through tidal heating. Europa: Ice, tidal heating, life in oceans?? Ganymede: Rock & Ice, past tectonics. Callisto: Rock, cratered terrain (impacts). GENS4001 X1 The Solar System 9 Saturn • • • • • • Lord of the Rings. Gas giant, much like Jupiter. Razor-thin rings of icy rocks (10 cm-10 m). Gravitational resonance with moons. At least 20 moons. Titan with nitrogen & hydrocarbon atmosphere, ethane oceans - life?? GENS4001 X1 The Solar System 10 Uranus • • • • • A bland gas giant. Tipped over – exaggerated seasons! Magnetic axis at 60° to rotation axis. 15 Moons, rings. Miranda: almost shattered by collision. GENS4001 X1 The Solar System 11 Neptune • A blue gas-giant, similar to Uranus. • Discovered through prediction from discrepancy in motion of Uranus. • Fastest winds in solar system (1700 km/hr)! • 8 moons, rings. • Triton captured - retrograde orbit. Extreme cold (36K) but nitrogen geysers! Being pulled into Neptune by tides! GENS4001 X1 The Solar System 12 Pluto + Charon • • • • Not really a planet - a double moon system. Discovered by chance in 1930. Now furthest from Sun (again, just!). Rock & ice. GENS4001 X1 The Solar System 13 Comets and Asteroids • • • • Debris from formation of Solar System. Asteroids: lumps of rock a few km in size. Most in belt between Mars & Jupiter. Comets: primordial balls of ices and rocks: transient dirty snowballs. • Highly elliptical orbits, from Kuiper Belt (50-500AU) or Oort Cloud (to 50,000AU). • Tails only when near Sun (vaporised ice), blown out by the solar wind & sunlight.