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Revision Lecture Monday 14, 2009 Tides • Ocean tides on Earth – The effect of Sun and Moon • Tides on the Moon • Tides on Io • Tides on Mercury Magnetic fields • • • • Generation Aurorae (Earth, Jupiter, Saturn) Induced magnetic field Magnetic field of the Sun and the solar cycle. The age of the Solar System • • • • • • 4.56 billion years 4.56 x 109 years 4.56 giga years (Gyr) 4560 million years Billion = 109 = giga Difference between American and British use of “billion” Chemical Symbols • Methane CH4 • Ammonia NH3 • Oxygen and nitrogen molecules O2 and N2 • Carbon dioxide CO2 • Carbon monoxide CO • Sufur dioxide SO2 • Sulfuric acid H2SO4 Their planets of choice: • • • • • • • CH4 – J. S. U. N. NH3 – J. S. O2 and N2 - Earth CO2 – Venus, Mars CO SO2 - Venus H2SO4 - Venus Temperatures • Celcius vs. Kelvin: Remember 0o C = 273 K or 0 K = -273o C • What solar system body has a surface T of 40 K? • What is the surface temperature of Venus? Does it vary from night to day? • What is the surface temperature of Mercury? Does it vary from night to day? Why the difference between Mercury and Venus? Resonances • The dynamics of a system with more than 2 bodies is complex and generates resonances. • The system tries to achieve the lowest energy = highest stability. • As everything orbits, some resonances are stable (Pluto-Neptune; Io, Europa and Ganymede). Others are not stable (cleared gaps in Saturn’s rings). Planetary densities • • • • • • Determination: Mass/Volume Volume = 4/3 p R3 Mean density of Earth = 5515 kg/m3 Density of rock ≈ 3000 kg/m3 Density of water = 1000 kg/m3 = 1 gr/cm3 What do you deduce of a planet has mean density << 3000 kg/m3? Impacts and impact craters • What was the era of heavy bombardment? • Where are craters seen? • What do many craters mean? • What planets/areas of planets/moons have many craters? What have few? The Greenhouse effect • On Earth • On Venus • On Mars Tectonic activity Earth: plate tectonic Venus: “flake” tectonic Mars: Valles Marineris. Importance of crust thickness on type of tectonic activity. • Ganymede: fractures on both light and dark lands – tectonic activity. • • • • Internal heat • Evidence: – Recent tectonic activity seen on surface – Own magnetic field • Likelyhood: – larger bodies retain heat more readily – they cool more slowly – terrestrial planets activity as a function of mass. – Bodies which are tidally stressed can be kept warm (Io). • Strange examples: – Ganymede – Titan (reheating?) – Enceladus (tidal?) Liquid, solid or gas? Space Missions Mercury: Mariner 10, Messenger Venus: Venera, Magellan Mars: Vikings 1-4, Pathfinder, Rovers … Jupiter: Pioneers 10,11, Voyagers 1,2, Galileo • Saturn: Voyagers 1,2, Cassini • Uranus + Neptune: Voyagers 1,2 • Pluto: New Horizons • • • •